Merge pull request 'Another CDS timestamp bugfix' (#8) from another_logic_fix_cds_stamp into main

Reviewed-on: #8

.github/workflows/ci.yml

@@ -20,6 +20,21 @@ jobs:
           command: check
           args: --release
 
+  msrv:
+    name: Check with MSRV
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: 1.60.0
+          override: true
+          profile: minimal
+      - uses: actions-rs/cargo@v1
+        with:
+          command: check
+          args: --release
+
   cross-check:
     name: Check Cross
     runs-on: ubuntu-latest
@@ -58,6 +73,21 @@ jobs:
           command: fmt
           args: --all -- --check
 
+  check-doc:
+    name: Check Documentation Build
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: nightly
+          override: true
+          profile: minimal
+      - uses: actions-rs/cargo@v1
+        with:
+          command: doc
+          args: --all-features
+
   clippy:
     name: Clippy
     runs-on: ubuntu-latest

CHANGELOG.md

@@ -8,6 +8,67 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 # [unreleased]
 
+# [v0.4.2] 14.01.2023
+
+## Fixed
+
+- CDS timestamp: Fixed another small logic error for stamp creation from the current
+  time with picosecond precision.
+  PR: https://egit.irs.uni-stuttgart.de/rust/spacepackets/pulls/8
+
+# [v0.4.1] 14.01.2023
+
+## Fixed
+
+- CDS timestamp: The conversion function from the current time were buggy
+  when specifying picoseconds precision, which could lead to overflow
+  multiplications and/or incorrect precision fields.
+  PR: https://egit.irs.uni-stuttgart.de/rust/spacepackets/pulls/7
+
+# [v0.4.0] 10.01.2023
+
+## Fixed
+
+- Remove `Default` derive on CDS time provider. This can lead to uninitialized preamble fields.
+
+## Changed
+
+- `serde` support is now optional and behind the `serde` feature.
+- `PusTcSecondaryHeaderT` trait renamed to `GenericPusTcSecondaryHeader`.
+- `PusTmSecondaryHeaderT` trait renamed to `GenericPusTmSecondaryHeader`.
+- `SpHeader`: Former `tc` and `tm` methods now named `tc_unseg` and `tm_unseg`.
+  Former `new` method now called `new_from_single_fields`.
+- `SpHeader`: Renamed `from_bytes` to `from_be_bytes`.
+  The function now returns the remaining slice as well.
+- All CDS specific functionality was moved into the `cds` submodule of the `time`
+  module. `CdsShortTimeProvider` was renamed to `TimeProvider`.
+  PR: https://egit.irs.uni-stuttgart.de/rust/spacepackets/pulls/3
+
+## Added
+
+- `SpHeader` getter function `sp_header` added for `PusTc`
+  PR: https://egit.irs.uni-stuttgart.de/rust/spacepackets/pulls/6
+- Added PFC enumerations: `ecss::UnsignedPfc` and `ecss::RealPfc`.
+  PR: https://egit.irs.uni-stuttgart.de/rust/spacepackets/pulls/5
+- Added `std::error::Error` implementation for all error enumerations if the `std` feature
+  is enabled.
+- CUC timestamp implementation as specified in CCSDS 301.0-B-4 section 3.2.
+  PR: https://egit.irs.uni-stuttgart.de/rust/spacepackets/pulls/4/files
+- ACII timestamps as specified in CCSDS 301.0-B-4 section 3.5.
+- Added MSRV in `Cargo.toml` with the `rust-version` field set to Rust 1.60.
+- `serde` `Serialize` and `Deserialize` added to all types.
+- Added `const` constructors for `PacketId`, `PacketSeqCtrl` and
+  `SpHeader`.
+- Added `PartialEq` and `Eq` `derive`s to `TimeProvider`.
+- `SpHeader`: Added serialization function into raw format `write_to_be_bytes`.
+- Added 24-bit day field support for CDS short. The bit width is configured at type level
+  via a generic parameter type passed to the `cds::TimeProvider`
+- Added submillisecond precision support for `cds::TimeProvider`
+
+# [v0.3.1] 03.12.2022
+
+- Small fix for faulty docs.rs build
+
 # [v0.3.0] 01.12.2022
 
 ## Added

Cargo.toml

@@ -1,7 +1,8 @@
 [package]
 name = "spacepackets"
-version = "0.3.0"
+version = "0.4.2"
 edition = "2021"
+rust-version = "1.60"
 authors = ["Robin Mueller <muellerr@irs.uni-stuttgart.de>"]
 description = "Generic implementations for various CCSDS and ECSS packet standards"
 homepage = "https://egit.irs.uni-stuttgart.de/rust/spacepackets"
@@ -13,11 +14,12 @@ categories = ["aerospace", "aerospace::space-protocols", "no-std", "hardware-sup
 
 [dependencies]
 zerocopy = "0.6"
-crc = "3.0"
+crc = "3"
 delegate = "0.8"
 
 [dependencies.serde]
-version = "1.0"
+version = "1"
+optional = true
 default-features = false
 features = ["derive"]
 
@@ -35,7 +37,8 @@ version = "1.0"
 [features]
 default = ["std"]
 std = ["chrono/std", "chrono/clock", "alloc"]
-alloc = ["postcard/alloc"]
+serde = ["dep:serde", "chrono/serde"]
+alloc = ["postcard/alloc", "chrono/alloc"]
 
 [package.metadata.docs.rs]
 all-features = true

README.md

@@ -15,25 +15,32 @@ Currently, this includes the following components:
   [CCSDS Blue Book 133.0-B-2](https://public.ccsds.org/Pubs/133x0b2e1.pdf)
 - PUS Telecommand and PUS Telemetry implementation according to the
   [ECSS-E-ST-70-41C standard](https://ecss.nl/standard/ecss-e-st-70-41c-space-engineering-telemetry-and-telecommand-packet-utilization-15-april-2016/).
-- CDS Short Time Code implementation according to
-  [CCSDS CCSDS 301.0-B-4](https://public.ccsds.org/Pubs/301x0b4e1.pdf)
- 
+- CUC (CCSDS Unsegmented Time Code) implementation according to
+  [CCSDS 301.0-B-4 3.2](https://public.ccsds.org/Pubs/301x0b4e1.pdf)
+- CDS (CCSDS Day Segmented Time Code) implementation according to
+  [CCSDS 301.0-B-4 3.3](https://public.ccsds.org/Pubs/301x0b4e1.pdf)
+- Some helper types to support ASCII timecodes ad specified in
+  [CCSDS 301.0-B-4 3.5](https://public.ccsds.org/Pubs/301x0b4e1.pdf)
+
 # Features
 
 `spacepackets` supports various runtime environments and is also suitable for `no_std` environments.
 
-It offers support for [`serde`](https://serde.rs/). The Space Packet, PUS TM and TC
-implementations derive the `serde` `Serialize` and `Deserialize` trait. This allows serializing and
+It also offers optional support for [`serde`](https://serde.rs/). This allows serializing and
 deserializing them with an appropriate `serde` provider like
 [`postcard`](https://github.com/jamesmunns/postcard).
 
-Default features:
+## Default features
 
  - [`std`](https://doc.rust-lang.org/std/): Enables functionality relying on the standard library.
  - [`alloc`](https://doc.rust-lang.org/alloc/): Enables features which operate on containers
    like [`alloc::vec::Vec`](https://doc.rust-lang.org/beta/alloc/vec/struct.Vec.html).
    Enabled by the `std` feature.
 
+## Optional Features
+
+ - [`serde`](https://serde.rs/): Adds `serde` support for most types by adding `Serialize` and `Deserialize` `derive`s
+
 # Examples
 
 You can check the [documentation](https://docs.rs/spacepackets) of individual modules for various

automation/Dockerfile

@@ -10,6 +10,6 @@ ARG DEBIAN_FRONTEND=noninteractive
 # set CROSS_CONTAINER_IN_CONTAINER to inform `cross` that it is executed from within a container
 ENV CROSS_CONTAINER_IN_CONTAINER=true
 
-# TODO: installing cross is problematic, permission issues
-RUN rustup target add thumbv7em-none-eabihf armv7-unknown-linux-gnueabihf && \
+RUN rustup install nightly && \
+    rustup target add thumbv7em-none-eabihf armv7-unknown-linux-gnueabihf && \
     rustup component add rustfmt clippy

automation/Jenkinsfile

@@ -13,19 +13,29 @@ pipeline {
                 sh 'cargo clippy'
             }
         }
+        stage('Docs') {
+            steps {
+                sh 'cargo +nightly doc --all-features'
+            }
+        }
         stage('Rustfmt') {
             steps {
-                sh 'cargo fmt'
+                sh 'cargo fmt --all --check'
             }
         }
         stage('Test') {
             steps {
-                sh 'cargo test'
+                sh 'cargo test --all-features'
             }
         }
-        stage('Check') {
+        stage('Check with all features') {
             steps {
-                sh 'cargo check'
+                sh 'cargo check --all-features'
+            }
+        }
+        stage('Check with no features') {
+            steps {
+                sh 'cargo check --no-default-features'
             }
         }
         stage('Check Cross Embedded Bare Metal') {

src/ecss.rs

@@ -1,10 +1,13 @@
 //! Common definitions and helpers required to create PUS TMTC packets according to
 //! [ECSS-E-ST-70-41C](https://ecss.nl/standard/ecss-e-st-70-41c-space-engineering-telemetry-and-telecommand-packet-utilization-15-april-2016/)
 use crate::{ByteConversionError, CcsdsPacket, SizeMissmatch};
-use core::fmt::Debug;
+use core::fmt::{Debug, Display, Formatter};
 use core::mem::size_of;
 use crc::{Crc, CRC_16_IBM_3740};
+#[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
+#[cfg(feature = "std")]
+use std::error::Error;
 
 pub type CrcType = u16;
 
@@ -12,8 +15,24 @@ pub type CrcType = u16;
 pub const CRC_CCITT_FALSE: Crc<u16> = Crc::<u16>::new(&CRC_16_IBM_3740);
 pub const CCSDS_HEADER_LEN: usize = size_of::<crate::zc::SpHeader>();
 
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub enum PusServiceId {
+    /// Service 1
+    Verification = 1,
+    /// Service 3
+    Housekeeping = 3,
+    /// Service 5
+    Event = 5,
+    /// Service 8
+    Action = 8,
+    /// Service 17
+    Test = 17,
+}
+
 /// All PUS versions. Only PUS C is supported by this library.
-#[derive(PartialEq, Eq, Copy, Clone, Serialize, Deserialize, Debug)]
+#[derive(PartialEq, Eq, Copy, Clone, Debug)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub enum PusVersion {
     EsaPus = 0,
     PusA = 1,
@@ -34,7 +53,9 @@ impl TryFrom<u8> for PusVersion {
     }
 }
 
+/// ECSS Packet Type Codes (PTC)s.
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub enum PacketTypeCodes {
     Boolean = 1,
     Enumerated = 2,
@@ -50,7 +71,40 @@ pub enum PacketTypeCodes {
     Packet = 12,
 }
 
+pub type Ptc = PacketTypeCodes;
+
+/// ECSS Packet Field Codes (PFC)s for the unsigned [Ptc].
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub enum UnsignedPfc {
+    OneByte = 4,
+    TwelveBits = 8,
+    TwoBytes = 12,
+    ThreeBytes = 13,
+    FourBytes = 14,
+    SixBytes = 15,
+    EightBytes = 16,
+    OneBit = 17,
+    TwoBits = 18,
+    ThreeBits = 19,
+}
+
+/// ECSS Packet Field Codes (PFC)s for the real (floating point) [Ptc].
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub enum RealPfc {
+    /// 4 octets simple precision format (IEEE)
+    Float = 1,
+    /// 8 octets simple precision format (IEEE)
+    Double = 2,
+    /// 4 octets simple precision format (MIL-STD)
+    FloatMilStd = 3,
+    /// 8 octets simple precision format (MIL-STD)
+    DoubleMilStd = 4,
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub enum PusError {
     VersionNotSupported(PusVersion),
     IncorrectCrc(u16),
@@ -61,12 +115,53 @@ pub enum PusError {
     ByteConversionError(ByteConversionError),
 }
 
+impl Display for PusError {
+    fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
+        match self {
+            PusError::VersionNotSupported(v) => {
+                write!(f, "PUS version {:?} not supported", v)
+            }
+            PusError::IncorrectCrc(crc) => {
+                write!(f, "crc16 {:#04x} is incorrect", crc)
+            }
+            PusError::RawDataTooShort(size) => {
+                write!(
+                    f,
+                    "deserialization error, provided raw data with size {} too short",
+                    size
+                )
+            }
+            PusError::NoRawData => {
+                write!(f, "no raw data provided")
+            }
+            PusError::CrcCalculationMissing => {
+                write!(f, "crc16 was not calculated")
+            }
+            PusError::ByteConversionError(e) => {
+                write!(f, "low level byte conversion error: {}", e)
+            }
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl Error for PusError {
+    fn source(&self) -> Option<&(dyn Error + 'static)> {
+        if let PusError::ByteConversionError(e) = self {
+            return Some(e);
+        }
+        None
+    }
+}
+
 impl From<ByteConversionError> for PusError {
     fn from(e: ByteConversionError) -> Self {
         PusError::ByteConversionError(e)
     }
 }
 
+/// Generic trait to describe common attributes for both PUS Telecommands (TC) and PUS Telemetry
+/// (TM) packets. All PUS packets are also a special type of [CcsdsPacket]s.
 pub trait PusPacket: CcsdsPacket {
     const PUS_VERSION: PusVersion = PusVersion::PusC;
 
@@ -179,6 +274,14 @@ pub trait ToBeBytes {
     fn to_be_bytes(&self) -> Self::ByteArray;
 }
 
+impl ToBeBytes for () {
+    type ByteArray = [u8; 0];
+
+    fn to_be_bytes(&self) -> Self::ByteArray {
+        []
+    }
+}
+
 impl ToBeBytes for u8 {
     type ByteArray = [u8; 1];
 
@@ -212,6 +315,7 @@ impl ToBeBytes for u64 {
 }
 
 #[derive(Debug, Copy, Clone, Eq, PartialEq)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub struct GenericEcssEnumWrapper<TYPE> {
     val: TYPE,
 }
@@ -232,13 +336,13 @@ impl<TYPE: ToBeBytes> EcssEnumeration for GenericEcssEnumWrapper<TYPE> {
     }
 
     fn write_to_be_bytes(&self, buf: &mut [u8]) -> Result<(), ByteConversionError> {
-        if buf.len() < self.byte_width() as usize {
+        if buf.len() < self.byte_width() {
             return Err(ByteConversionError::ToSliceTooSmall(SizeMissmatch {
                 found: buf.len(),
-                expected: self.byte_width() as usize,
+                expected: self.byte_width(),
             }));
         }
-        buf[0..self.byte_width() as usize].copy_from_slice(self.val.to_be_bytes().as_ref());
+        buf[0..self.byte_width()].copy_from_slice(self.val.to_be_bytes().as_ref());
         Ok(())
     }
 }

src/lib.rs

@@ -9,47 +9,63 @@
 //!    [CCSDS Blue Book 133.0-B-2](https://public.ccsds.org/Pubs/133x0b2e1.pdf)
 //!  - PUS Telecommand and PUS Telemetry implementation according to the
 //!    [ECSS-E-ST-70-41C standard](https://ecss.nl/standard/ecss-e-st-70-41c-space-engineering-telemetry-and-telecommand-packet-utilization-15-april-2016/).
-//!  - CDS Short Time Code implementation according to
-//!    [CCSDS CCSDS 301.0-B-4](https://public.ccsds.org/Pubs/301x0b4e1.pdf)
+//!  - CUC (CCSDS Unsegmented Time Code) implementation according to
+//!    [CCSDS 301.0-B-4 3.2](https://public.ccsds.org/Pubs/301x0b4e1.pdf)
+//!  - CDS (CCSDS Day Segmented Time Code) implementation according to
+//!    [CCSDS 301.0-B-4 3.3](https://public.ccsds.org/Pubs/301x0b4e1.pdf)
+//!  - Some helper types to support ASCII timecodes ad specified in
+//!    [CCSDS 301.0-B-4 3.5](https://public.ccsds.org/Pubs/301x0b4e1.pdf)
 //!
 //! ## Features
 //!
 //! `spacepackets` supports various runtime environments and is also suitable for `no_std` environments.
 //!
-//! It also offers support for [`serde`](https://serde.rs/). The Space Packet, PUS TM and TC
-//! implementations derive the `serde` `Serialize` and `Deserialize` trait. This allows serializing and
+//! It also offers optional support for [`serde`](https://serde.rs/). This allows serializing and
 //! deserializing them with an appropriate `serde` provider like
 //! [`postcard`](https://github.com/jamesmunns/postcard).
 //!
-//! Default features:
+//! ### Default features
 //!
 //!  - [`std`](https://doc.rust-lang.org/std/): Enables functionality relying on the standard library.
 //!  - [`alloc`](https://doc.rust-lang.org/alloc/): Enables features which operate on containers
 //!     like [`alloc::vec::Vec`](https://doc.rust-lang.org/beta/alloc/vec/struct.Vec.html).
 //!     Enabled by the `std` feature.
 //!
+//! ### Optional features
+//!
+//!  - [`serde`](https://serde.rs/): Adds `serde` support for most types by adding `Serialize` and
+//!    `Deserialize` `derive`s
+//!
 //! ## Module
 //!
 //! This module contains helpers and data structures to generate Space Packets according to the
 //! [CCSDS 133.0-B-2](https://public.ccsds.org/Pubs/133x0b2e1.pdf). This includes the
-//! [SpHeader] class to generate the Space Packet Header component common to all space packets
+//! [SpHeader] class to generate the Space Packet Header component common to all space packets.
 //!
 //! ## Example
 //!
 //! ```rust
 //! use spacepackets::SpHeader;
-//! let sp_header = SpHeader::tc(0x42, 12, 0).expect("Error creating SP header");
+//! let sp_header = SpHeader::tc_unseg(0x42, 12, 1).expect("Error creating CCSDS TC header");
 //! println!("{:?}", sp_header);
+//! let mut ccsds_buf: [u8; 32] = [0; 32];
+//! sp_header.write_to_be_bytes(&mut ccsds_buf).expect("Writing CCSDS TC header failed");
+//! println!("{:x?}", &ccsds_buf[0..6]);
 //! ```
 #![no_std]
+#![cfg_attr(doc_cfg, feature(doc_cfg))]
 #[cfg(feature = "alloc")]
 extern crate alloc;
 #[cfg(any(feature = "std", test))]
 extern crate std;
 
 use crate::ecss::CCSDS_HEADER_LEN;
+use core::fmt::{Display, Formatter};
 use delegate::delegate;
+#[cfg(feature = "std")]
+use std::error::Error;
 
+#[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
 
 pub mod ecss;
@@ -57,16 +73,22 @@ pub mod tc;
 pub mod time;
 pub mod tm;
 
+mod private {
+    pub trait Sealed {}
+}
+
 pub const MAX_APID: u16 = 2u16.pow(11) - 1;
 pub const MAX_SEQ_COUNT: u16 = 2u16.pow(14) - 1;
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub struct SizeMissmatch {
     pub found: usize,
     pub expected: usize,
 }
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub enum ByteConversionError {
     /// The passed slice is too small. Returns the passed slice length and expected minimum size
     ToSliceTooSmall(SizeMissmatch),
@@ -77,7 +99,39 @@ pub enum ByteConversionError {
     ZeroCopyFromError,
 }
 
-#[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Copy, Clone)]
+impl Display for ByteConversionError {
+    fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
+        match self {
+            ByteConversionError::ToSliceTooSmall(missmatch) => {
+                write!(
+                    f,
+                    "target slice with size {} is too small, expected size of at least {}",
+                    missmatch.found, missmatch.expected
+                )
+            }
+            ByteConversionError::FromSliceTooSmall(missmatch) => {
+                write!(
+                    f,
+                    "source slice with size {} too small, expected at least {} bytes",
+                    missmatch.found, missmatch.expected
+                )
+            }
+            ByteConversionError::ZeroCopyToError => {
+                write!(f, "zerocopy serialization error")
+            }
+            ByteConversionError::ZeroCopyFromError => {
+                write!(f, "zerocopy deserialization error")
+            }
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl Error for ByteConversionError {}
+
+/// CCSDS packet type enumeration.
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub enum PacketType {
     Tm = 0,
     Tc = 1,
@@ -99,7 +153,8 @@ pub fn packet_type_in_raw_packet_id(packet_id: u16) -> PacketType {
     PacketType::try_from((packet_id >> 12) as u8 & 0b1).unwrap()
 }
 
-#[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Copy, Clone)]
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub enum SequenceFlags {
     ContinuationSegment = 0b00,
     FirstSegment = 0b01,
@@ -123,21 +178,59 @@ impl TryFrom<u8> for SequenceFlags {
     }
 }
 
-#[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Copy, Clone)]
+/// Abstraction for the CCSDS Packet ID, which forms the last thirteen bits
+/// of the first two bytes in the CCSDS primary header.
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub struct PacketId {
     pub ptype: PacketType,
     pub sec_header_flag: bool,
     apid: u16,
 }
 
-impl PacketId {
-    pub fn new(ptype: PacketType, sec_header_flag: bool, apid: u16) -> Option<PacketId> {
-        let mut pid = PacketId {
-            ptype,
-            sec_header_flag,
+impl Default for PacketId {
+    fn default() -> Self {
+        PacketId {
+            ptype: PacketType::Tm,
+            sec_header_flag: false,
             apid: 0,
-        };
-        pid.set_apid(apid).then_some(pid)
+        }
+    }
+}
+
+impl PacketId {
+    pub const fn const_tc(sec_header: bool, apid: u16) -> Self {
+        Self::const_new(PacketType::Tc, sec_header, apid)
+    }
+
+    pub const fn const_tm(sec_header: bool, apid: u16) -> Self {
+        Self::const_new(PacketType::Tm, sec_header, apid)
+    }
+
+    pub fn tc(sec_header: bool, apid: u16) -> Option<Self> {
+        Self::new(PacketType::Tc, sec_header, apid)
+    }
+
+    pub fn tm(sec_header: bool, apid: u16) -> Option<Self> {
+        Self::new(PacketType::Tm, sec_header, apid)
+    }
+
+    pub const fn const_new(ptype: PacketType, sec_header: bool, apid: u16) -> Self {
+        if apid > MAX_APID {
+            panic!("APID too large");
+        }
+        PacketId {
+            ptype,
+            sec_header_flag: sec_header,
+            apid,
+        }
+    }
+
+    pub fn new(ptype: PacketType, sec_header_flag: bool, apid: u16) -> Option<PacketId> {
+        if apid > MAX_APID {
+            return None;
+        }
+        Some(PacketId::const_new(ptype, sec_header_flag, apid))
     }
 
     /// Set a new Application Process ID (APID). If the passed number is invalid, the APID will
@@ -170,27 +263,41 @@ impl From<u16> for PacketId {
     }
 }
 
-#[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Copy, Clone)]
+/// Abstraction for the CCSDS Packet Sequence Control (PSC) field which is the
+/// third and the fourth byte in the CCSDS primary header.
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub struct PacketSequenceCtrl {
     pub seq_flags: SequenceFlags,
     seq_count: u16,
 }
 
 impl PacketSequenceCtrl {
-    /// Returns [None] if the passed sequence count exceeds [MAX_SEQ_COUNT]
-    pub fn new(seq_flags: SequenceFlags, seq_count: u16) -> Option<PacketSequenceCtrl> {
-        let mut psc = PacketSequenceCtrl {
+    /// const variant of [PacketSequenceCtrl::new], but panics if the sequence count exceeds
+    /// [MAX_SEQ_COUNT].
+    const fn const_new(seq_flags: SequenceFlags, seq_count: u16) -> PacketSequenceCtrl {
+        if seq_count > MAX_SEQ_COUNT {
+            panic!("Sequence count too large");
+        }
+        PacketSequenceCtrl {
             seq_flags,
-            seq_count: 0,
-        };
-        psc.set_seq_count(seq_count).then_some(psc)
+            seq_count,
+        }
+    }
+
+    /// Returns [None] if the passed sequence count exceeds [MAX_SEQ_COUNT].
+    pub fn new(seq_flags: SequenceFlags, seq_count: u16) -> Option<PacketSequenceCtrl> {
+        if seq_count > MAX_SEQ_COUNT {
+            return None;
+        }
+        Some(PacketSequenceCtrl::const_new(seq_flags, seq_count))
     }
     pub fn raw(&self) -> u16 {
         ((self.seq_flags as u16) << 14) | self.seq_count
     }
 
     /// Set a new sequence count. If the passed number is invalid, the sequence count will not be
-    /// set and false will be returned. The maximum allowed value for the 14-bit field is 16383
+    /// set and false will be returned. The maximum allowed value for the 14-bit field is 16383.
     pub fn set_seq_count(&mut self, ssc: u16) -> bool {
         if ssc > MAX_SEQ_COUNT {
             return false;
@@ -231,7 +338,7 @@ macro_rules! sph_from_other {
 const SSC_MASK: u16 = 0x3FFF;
 const VERSION_MASK: u16 = 0xE000;
 
-/// Generic trait to access fields of a CCSDS space packet header according to CCSDS 133.0-B-2
+/// Generic trait to access fields of a CCSDS space packet header according to CCSDS 133.0-B-2.
 pub trait CcsdsPacket {
     fn ccsds_version(&self) -> u8;
     fn packet_id(&self) -> PacketId;
@@ -245,7 +352,7 @@ pub trait CcsdsPacket {
     }
 
     /// Retrieve 13 bit Packet Identification field. Can usually be retrieved with a bitwise AND
-    /// of the first 2 bytes with 0x1FFF
+    /// of the first 2 bytes with 0x1FFF.
     #[inline]
     fn packet_id_raw(&self) -> u16 {
         self.packet_id().raw()
@@ -256,8 +363,8 @@ pub trait CcsdsPacket {
         self.psc().raw()
     }
 
+    /// Retrieve Packet Type (TM: 0, TC: 1).
     #[inline]
-    /// Retrieve Packet Type (TM: 0, TC: 1)
     fn ptype(&self) -> PacketType {
         // This call should never fail because only 0 and 1 can be passed to the try_from call
         self.packet_id().ptype
@@ -274,13 +381,13 @@ pub trait CcsdsPacket {
     }
 
     /// Retrieve the secondary header flag. Returns true if a secondary header is present
-    /// and false if it is not
+    /// and false if it is not.
     #[inline]
     fn sec_header_flag(&self) -> bool {
         self.packet_id().sec_header_flag
     }
 
-    /// Retrieve Application Process ID
+    /// Retrieve Application Process ID.
     #[inline]
     fn apid(&self) -> u16 {
         self.packet_id().apid
@@ -308,16 +415,18 @@ pub trait CcsdsPrimaryHeader {
     ) -> Self;
 }
 
-/// Space Packet Primary Header according to CCSDS 133.0-B-2
+/// Space Packet Primary Header according to CCSDS 133.0-B-2.
 ///
 /// # Arguments
 ///
-/// * `version` - CCSDS version field, occupies the first 3 bits of the raw header
+/// * `version` - CCSDS version field, occupies the first 3 bits of the raw header. Will generally
+///    be set to 0b000 in all constructors provided by this crate.
 /// * `packet_id` - Packet Identifier, which can also be used as a start marker. Occupies the last
 ///    13 bits of the first two bytes of the raw header
 /// * `psc` - Packet Sequence Control, occupies the third and fourth byte of the raw header
 /// * `data_len` - Data length field occupies the fifth and the sixth byte of the raw header
-#[derive(serde::Serialize, serde::Deserialize, Debug, PartialEq, Eq, Copy, Clone)]
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub struct SpHeader {
     pub version: u8,
     pub packet_id: PacketId,
@@ -326,63 +435,104 @@ pub struct SpHeader {
 }
 
 impl Default for SpHeader {
+    /// The default function sets the sequence flag field to [SequenceFlags::Unsegmented]. The data
+    /// length field is set to 1, which denotes an empty space packets.
     fn default() -> Self {
         SpHeader {
             version: 0,
-            packet_id: PacketId {
-                ptype: PacketType::Tm,
-                apid: 0,
-                sec_header_flag: false,
-            },
+            packet_id: PacketId::default(),
             psc: PacketSequenceCtrl {
                 seq_flags: SequenceFlags::Unsegmented,
                 seq_count: 0,
             },
-            data_len: 0,
+            data_len: 1,
         }
     }
 }
+
 impl SpHeader {
-    /// Create a new Space Packet Header instance which can be used to create generic
-    /// Space Packets. This will return [None] if the APID or sequence count argument
-    /// exceed [MAX_APID] or [MAX_SEQ_COUNT] respectively.
-    pub fn new(
+    pub const fn new(packet_id: PacketId, psc: PacketSequenceCtrl, data_len: u16) -> Self {
+        Self {
+            version: 0,
+            packet_id,
+            psc,
+            data_len,
+        }
+    }
+
+    /// const variant of the [SpHeader::new_fron_single_fields] function. Panics if the passed
+    /// APID exceeds [MAX_APID] or the passed packet sequence count exceeds [MAX_SEQ_COUNT].
+    const fn const_new_from_single_fields(
         ptype: PacketType,
         sec_header: bool,
         apid: u16,
+        seq_flags: SequenceFlags,
+        seq_count: u16,
+        data_len: u16,
+    ) -> Self {
+        if seq_count > MAX_SEQ_COUNT {
+            panic!("Sequence count is too large");
+        }
+        if apid > MAX_APID {
+            panic!("APID is too large");
+        }
+        Self {
+            psc: PacketSequenceCtrl::const_new(seq_flags, seq_count),
+            packet_id: PacketId::const_new(ptype, sec_header, apid),
+            data_len,
+            version: 0,
+        }
+    }
+
+    /// Create a new Space Packet Header instance which can be used to create generic
+    /// Space Packets. This will return [None] if the APID or sequence count argument
+    /// exceed [MAX_APID] or [MAX_SEQ_COUNT] respectively. The version field is set to 0b000.
+    pub fn new_from_single_fields(
+        ptype: PacketType,
+        sec_header: bool,
+        apid: u16,
+        seq_flags: SequenceFlags,
         seq_count: u16,
         data_len: u16,
     ) -> Option<Self> {
         if seq_count > MAX_SEQ_COUNT || apid > MAX_APID {
             return None;
         }
-        let mut header = SpHeader::default();
-        header.packet_id.sec_header_flag = sec_header;
-        header.packet_id.apid = apid;
-        header.packet_id.ptype = ptype;
-        header.psc.seq_count = seq_count;
-        header.data_len = data_len;
-        Some(header)
+        Some(SpHeader::const_new_from_single_fields(
+            ptype, sec_header, apid, seq_flags, seq_count, data_len,
+        ))
     }
 
-    /// Helper function for telemetry space packet headers. The packet type  field will be
-    /// set accordingly.
-    pub fn tm(apid: u16, seq_count: u16, data_len: u16) -> Option<Self> {
-        Self::new(PacketType::Tm, false, apid, seq_count, data_len)
+    /// Helper function for telemetry space packet headers. The packet type field will be
+    /// set accordingly. The secondary header flag field is set to false.
+    pub fn tm(apid: u16, seq_flags: SequenceFlags, seq_count: u16, data_len: u16) -> Option<Self> {
+        Self::new_from_single_fields(PacketType::Tm, false, apid, seq_flags, seq_count, data_len)
     }
 
-    /// Helper function for telecommand space packet headers. The packet type  field will be
-    /// set accordingly.
-    pub fn tc(apid: u16, seq_count: u16, data_len: u16) -> Option<Self> {
-        Self::new(PacketType::Tc, false, apid, seq_count, data_len)
+    /// Helper function for telemetry space packet headers. The packet type field will be
+    /// set accordingly. The secondary header flag field is set to false.
+    pub fn tc(apid: u16, seq_flags: SequenceFlags, seq_count: u16, data_len: u16) -> Option<Self> {
+        Self::new_from_single_fields(PacketType::Tc, false, apid, seq_flags, seq_count, data_len)
+    }
+
+    /// Variant of [SpHeader::tm] which sets the sequence flag field to [SequenceFlags::Unsegmented]
+    pub fn tm_unseg(apid: u16, seq_count: u16, data_len: u16) -> Option<Self> {
+        Self::tm(apid, SequenceFlags::Unsegmented, seq_count, data_len)
+    }
+
+    /// Variant of [SpHeader::tc] which sets the sequence flag field to [SequenceFlags::Unsegmented]
+    pub fn tc_unseg(apid: u16, seq_count: u16, data_len: u16) -> Option<Self> {
+        Self::tc(apid, SequenceFlags::Unsegmented, seq_count, data_len)
     }
 
     //noinspection RsTraitImplementation
     delegate!(to self.packet_id {
+        /// Returns [false] and fails if the APID exceeds [MAX_APID]
         pub fn set_apid(&mut self, apid: u16) -> bool;
     });
 
     delegate!(to self.psc {
+        /// Returns [false] and fails if the sequence count exceeds [MAX_SEQ_COUNT]
         pub fn set_seq_count(&mut self, seq_count: u16) -> bool;
     });
 
@@ -402,16 +552,38 @@ impl SpHeader {
         self.packet_id.ptype = packet_type;
     }
 
-    pub fn from_raw_slice(buf: &[u8]) -> Result<Self, ByteConversionError> {
-        if buf.len() < CCSDS_HEADER_LEN + 1 {
+    /// Create a struct from a raw slice where the fields have network endianness (big).
+    /// This function also returns the remaining part of the passed slice starting past the read
+    /// CCSDS header.
+    pub fn from_be_bytes(buf: &[u8]) -> Result<(Self, &[u8]), ByteConversionError> {
+        if buf.len() < CCSDS_HEADER_LEN {
             return Err(ByteConversionError::FromSliceTooSmall(SizeMissmatch {
                 found: buf.len(),
-                expected: CCSDS_HEADER_LEN + 1,
+                expected: CCSDS_HEADER_LEN,
             }));
         }
         let zc_header = zc::SpHeader::from_bytes(&buf[0..CCSDS_HEADER_LEN])
             .ok_or(ByteConversionError::ZeroCopyFromError)?;
-        Ok(Self::from(zc_header))
+        Ok((Self::from(zc_header), &buf[CCSDS_HEADER_LEN..]))
+    }
+
+    /// Write the header to a raw buffer using big endian format. This function returns the
+    /// remaining part of the passed slice starting past the written CCSDS header.
+    pub fn write_to_be_bytes<'a>(
+        &self,
+        buf: &'a mut [u8],
+    ) -> Result<&'a mut [u8], ByteConversionError> {
+        if buf.len() < CCSDS_HEADER_LEN {
+            return Err(ByteConversionError::FromSliceTooSmall(SizeMissmatch {
+                found: buf.len(),
+                expected: CCSDS_HEADER_LEN,
+            }));
+        }
+        let zc_header: zc::SpHeader = zc::SpHeader::from(*self);
+        zc_header
+            .to_bytes(&mut buf[0..CCSDS_HEADER_LEN])
+            .ok_or(ByteConversionError::ZeroCopyToError)?;
+        Ok(&mut buf[CCSDS_HEADER_LEN..])
     }
 }
 
@@ -540,23 +712,75 @@ pub mod zc {
     sph_from_other!(SpHeader, crate::SpHeader);
 }
 
-#[cfg(test)]
+#[cfg(all(test, feature = "std"))]
 mod tests {
-    #[cfg(feature = "std")]
+    #[cfg(feature = "serde")]
     use crate::CcsdsPrimaryHeader;
-    use crate::SpHeader;
     use crate::{
         packet_type_in_raw_packet_id, zc, CcsdsPacket, PacketId, PacketSequenceCtrl, PacketType,
-        SequenceFlags,
     };
+    use crate::{SequenceFlags, SpHeader};
     use alloc::vec;
-    #[cfg(not(feature = "std"))]
-    use num::pow;
-    #[cfg(feature = "std")]
     use num_traits::pow;
-    use postcard::from_bytes;
-    #[cfg(feature = "alloc")]
-    use postcard::to_allocvec;
+    #[cfg(feature = "serde")]
+    use postcard::{from_bytes, to_allocvec};
+
+    const CONST_SP: SpHeader = SpHeader::new(
+        PacketId::const_tc(true, 0x36),
+        PacketSequenceCtrl::const_new(SequenceFlags::ContinuationSegment, 0x88),
+        0x90,
+    );
+
+    const PACKET_ID_TM: PacketId = PacketId::const_tm(true, 0x22);
+
+    #[test]
+    fn verify_const_packet_id() {
+        assert_eq!(PACKET_ID_TM.apid(), 0x22);
+        assert_eq!(PACKET_ID_TM.sec_header_flag, true);
+        assert_eq!(PACKET_ID_TM.ptype, PacketType::Tm);
+        let const_tc_id = PacketId::const_tc(true, 0x23);
+        assert_eq!(const_tc_id.ptype, PacketType::Tc);
+    }
+
+    #[test]
+    fn test_default_packet_id() {
+        let id_default = PacketId::default();
+        assert_eq!(id_default.ptype, PacketType::Tm);
+        assert_eq!(id_default.apid, 0x000);
+        assert_eq!(id_default.sec_header_flag, false);
+    }
+
+    #[test]
+    fn test_packet_id_ctors() {
+        let packet_id = PacketId::new(PacketType::Tc, true, 0x1ff);
+        assert!(packet_id.is_some());
+        let packet_id = packet_id.unwrap();
+        assert_eq!(packet_id.apid(), 0x1ff);
+        assert_eq!(packet_id.ptype, PacketType::Tc);
+        assert_eq!(packet_id.sec_header_flag, true);
+        let packet_id_tc = PacketId::tc(true, 0x1ff);
+        assert!(packet_id_tc.is_some());
+        let packet_id_tc = packet_id_tc.unwrap();
+        assert_eq!(packet_id_tc, packet_id);
+        let packet_id_tm = PacketId::tm(true, 0x2ff);
+        assert!(packet_id_tm.is_some());
+        let packet_id_tm = packet_id_tm.unwrap();
+        assert_eq!(packet_id_tm.sec_header_flag, true);
+        assert_eq!(packet_id_tm.ptype, PacketType::Tm);
+        assert_eq!(packet_id_tm.apid, 0x2ff);
+    }
+
+    #[test]
+    fn verify_const_sp_header() {
+        assert_eq!(CONST_SP.sec_header_flag(), true);
+        assert_eq!(CONST_SP.apid(), 0x36);
+        assert_eq!(
+            CONST_SP.sequence_flags(),
+            SequenceFlags::ContinuationSegment
+        );
+        assert_eq!(CONST_SP.seq_count(), 0x88);
+        assert_eq!(CONST_SP.data_len, 0x90);
+    }
 
     #[test]
     fn test_seq_flag_helpers() {
@@ -639,9 +863,9 @@ mod tests {
     }
 
     #[test]
-    #[cfg(feature = "std")]
+    #[cfg(feature = "serde")]
     fn test_serde_sph() {
-        let sp_header = SpHeader::tc(0x42, 12, 0).expect("Error creating SP header");
+        let sp_header = SpHeader::tc_unseg(0x42, 12, 0).expect("Error creating SP header");
         assert_eq!(sp_header.ccsds_version(), 0b000);
         assert!(sp_header.is_tc());
         assert!(!sp_header.sec_header_flag());
@@ -663,7 +887,7 @@ mod tests {
         assert_eq!(sp_header.ccsds_version(), 0b000);
         assert_eq!(sp_header.data_len, 0);
 
-        let sp_header = SpHeader::tm(0x7, 22, 36).expect("Error creating SP header");
+        let sp_header = SpHeader::tm_unseg(0x7, 22, 36).expect("Error creating SP header");
         assert_eq!(sp_header.ccsds_version(), 0b000);
         assert!(sp_header.is_tm());
         assert!(!sp_header.sec_header_flag());
@@ -694,28 +918,69 @@ mod tests {
     }
 
     #[test]
-    fn test_sp_header_setters() {
-        let mut sp_header = SpHeader::tc(0x42, 12, 0).expect("Error creating SP header");
-        assert_eq!(sp_header.apid(), 0x42);
+    fn test_setters() {
+        let sp_header = SpHeader::tc(0x42, SequenceFlags::Unsegmented, 25, 0);
+        assert!(sp_header.is_some());
+        let mut sp_header = sp_header.unwrap();
         sp_header.set_apid(0x12);
         assert_eq!(sp_header.apid(), 0x12);
-
         sp_header.set_sec_header_flag();
         assert!(sp_header.sec_header_flag());
         sp_header.clear_sec_header_flag();
         assert!(!sp_header.sec_header_flag());
-        sp_header.set_seq_count(0x45);
-        assert_eq!(sp_header.seq_count(), 0x45);
         assert_eq!(sp_header.ptype(), PacketType::Tc);
         sp_header.set_packet_type(PacketType::Tm);
         assert_eq!(sp_header.ptype(), PacketType::Tm);
+        sp_header.set_seq_count(0x45);
+        assert_eq!(sp_header.seq_count(), 0x45);
+    }
+
+    #[test]
+    fn test_tc_ctor() {
+        let sp_header = SpHeader::tc(0x42, SequenceFlags::Unsegmented, 25, 0);
+        assert!(sp_header.is_some());
+        let sp_header = sp_header.unwrap();
+        verify_sp_fields(PacketType::Tc, &sp_header);
+    }
+
+    #[test]
+    fn test_tc_ctor_unseg() {
+        let sp_header = SpHeader::tc_unseg(0x42, 25, 0);
+        assert!(sp_header.is_some());
+        let sp_header = sp_header.unwrap();
+        verify_sp_fields(PacketType::Tc, &sp_header);
+    }
+
+    #[test]
+    fn test_tm_ctor() {
+        let sp_header = SpHeader::tm(0x42, SequenceFlags::Unsegmented, 25, 0);
+        assert!(sp_header.is_some());
+        let sp_header = sp_header.unwrap();
+        verify_sp_fields(PacketType::Tm, &sp_header);
+    }
+
+    #[test]
+    fn test_tm_ctor_unseg() {
+        let sp_header = SpHeader::tm_unseg(0x42, 25, 0);
+        assert!(sp_header.is_some());
+        let sp_header = sp_header.unwrap();
+        verify_sp_fields(PacketType::Tm, &sp_header);
+    }
+
+    fn verify_sp_fields(ptype: PacketType, sp_header: &SpHeader) {
+        assert_eq!(sp_header.ptype(), ptype);
+        assert_eq!(sp_header.sequence_flags(), SequenceFlags::Unsegmented);
+        assert_eq!(sp_header.apid(), 0x42);
+        assert_eq!(sp_header.seq_count(), 25);
+        assert_eq!(sp_header.data_len(), 0);
     }
 
     #[test]
     fn test_zc_sph() {
         use zerocopy::AsBytes;
 
-        let sp_header = SpHeader::tc(0x7FF, pow(2, 14) - 1, 0).expect("Error creating SP header");
+        let sp_header =
+            SpHeader::tc_unseg(0x7FF, pow(2, 14) - 1, 0).expect("Error creating SP header");
         assert_eq!(sp_header.ptype(), PacketType::Tc);
         assert_eq!(sp_header.apid(), 0x7FF);
         assert_eq!(sp_header.data_len(), 0);

src/tc.rs

@@ -9,7 +9,7 @@
 //! use spacepackets::ecss::PusPacket;
 //!
 //! // Create a ping telecommand with no user application data
-//! let mut sph = SpHeader::tc(0x02, 0x34, 0).unwrap();
+//! let mut sph = SpHeader::tc_unseg(0x02, 0x34, 0).unwrap();
 //! let tc_header = PusTcSecondaryHeader::new_simple(17, 1);
 //! let pus_tc = PusTc::new(&mut sph, tc_header, None, true);
 //! println!("{:?}", pus_tc);
@@ -41,6 +41,7 @@ use crate::{
 };
 use core::mem::size_of;
 use delegate::delegate;
+#[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
 use zerocopy::AsBytes;
 
@@ -66,7 +67,7 @@ pub const ACK_ALL: u8 = AckOpts::Acceptance as u8
     | AckOpts::Progress as u8
     | AckOpts::Completion as u8;
 
-pub trait PusTcSecondaryHeaderT {
+pub trait GenericPusTcSecondaryHeader {
     fn pus_version(&self) -> PusVersion;
     fn ack_flags(&self) -> u8;
     fn service(&self) -> u8;
@@ -76,7 +77,7 @@ pub trait PusTcSecondaryHeaderT {
 
 pub mod zc {
     use crate::ecss::{PusError, PusVersion};
-    use crate::tc::PusTcSecondaryHeaderT;
+    use crate::tc::GenericPusTcSecondaryHeader;
     use zerocopy::{AsBytes, FromBytes, NetworkEndian, Unaligned, U16};
 
     #[derive(FromBytes, AsBytes, Unaligned)]
@@ -103,7 +104,7 @@ pub mod zc {
         }
     }
 
-    impl PusTcSecondaryHeaderT for PusTcSecondaryHeader {
+    impl GenericPusTcSecondaryHeader for PusTcSecondaryHeader {
         fn pus_version(&self) -> PusVersion {
             PusVersion::try_from(self.version_ack >> 4 & 0b1111).unwrap_or(PusVersion::Invalid)
         }
@@ -136,7 +137,8 @@ pub mod zc {
     }
 }
 
-#[derive(PartialEq, Eq, Copy, Clone, Serialize, Deserialize, Debug)]
+#[derive(PartialEq, Eq, Copy, Clone, Debug)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub struct PusTcSecondaryHeader {
     pub service: u8,
     pub subservice: u8,
@@ -145,7 +147,7 @@ pub struct PusTcSecondaryHeader {
     pub version: PusVersion,
 }
 
-impl PusTcSecondaryHeaderT for PusTcSecondaryHeader {
+impl GenericPusTcSecondaryHeader for PusTcSecondaryHeader {
     fn pus_version(&self) -> PusVersion {
         self.version
     }
@@ -206,25 +208,26 @@ impl PusTcSecondaryHeader {
 /// This class models a PUS telecommand. It is the primary data structure to generate the raw byte
 /// representation of a PUS telecommand or to deserialize from one from raw bytes.
 ///
-/// This class also derives the [serde::Serialize] and [serde::Deserialize] trait which allows
-/// to send around TC packets in a raw byte format using a serde provider like
-/// [postcard](https://docs.rs/postcard/latest/postcard/).
+/// This class also derives the [serde::Serialize] and [serde::Deserialize] trait if the
+/// [serde] feature is used, which allows to send around TC packets in a raw byte format using a
+/// serde provider like [postcard](https://docs.rs/postcard/latest/postcard/).
 ///
 /// There is no spare bytes support yet.
-#[derive(PartialEq, Eq, Copy, Clone, Serialize, Deserialize, Debug)]
-pub struct PusTc<'slice> {
+#[derive(PartialEq, Eq, Copy, Clone, Debug)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub struct PusTc<'app_data> {
     sp_header: SpHeader,
     pub sec_header: PusTcSecondaryHeader,
     /// If this is set to false, a manual call to [PusTc::calc_own_crc16] or
     /// [PusTc::update_packet_fields] is necessary for the serialized or cached CRC16 to be valid.
     pub calc_crc_on_serialization: bool,
-    #[serde(skip)]
-    raw_data: Option<&'slice [u8]>,
-    app_data: Option<&'slice [u8]>,
+    #[cfg_attr(feature = "serde", serde(skip))]
+    raw_data: Option<&'app_data [u8]>,
+    app_data: Option<&'app_data [u8]>,
     crc16: Option<u16>,
 }
 
-impl<'slice> PusTc<'slice> {
+impl<'app_data> PusTc<'app_data> {
     /// Generates a new struct instance.
     ///
     /// # Arguments
@@ -240,7 +243,7 @@ impl<'slice> PusTc<'slice> {
     pub fn new(
         sp_header: &mut SpHeader,
         sec_header: PusTcSecondaryHeader,
-        app_data: Option<&'slice [u8]>,
+        app_data: Option<&'app_data [u8]>,
         set_ccsds_len: bool,
     ) -> Self {
         sp_header.set_packet_type(PacketType::Tc);
@@ -260,12 +263,12 @@ impl<'slice> PusTc<'slice> {
     }
 
     /// Simplified version of the [PusTc::new] function which allows to only specify service and
-    /// subservice instead of the full PUS TC secondary header
+    /// subservice instead of the full PUS TC secondary header.
     pub fn new_simple(
         sph: &mut SpHeader,
         service: u8,
         subservice: u8,
-        app_data: Option<&'slice [u8]>,
+        app_data: Option<&'app_data [u8]>,
         set_ccsds_len: bool,
     ) -> Self {
         Self::new(
@@ -276,6 +279,10 @@ impl<'slice> PusTc<'slice> {
         )
     }
 
+    pub fn sp_header(&self) -> &SpHeader {
+        &self.sp_header
+    }
+
     pub fn len_packed(&self) -> usize {
         let mut length = PUS_TC_MIN_LEN_WITHOUT_APP_DATA;
         if let Some(app_data) = self.app_data {
@@ -303,7 +310,7 @@ impl<'slice> PusTc<'slice> {
     /// used.
     /// If this was not done or the application data is set or changed after construction,
     /// this function needs to be called to ensure that the data length field of the CCSDS header
-    /// is set correctly
+    /// is set correctly.
     pub fn update_ccsds_data_len(&mut self) {
         self.sp_header.data_len =
             self.len_packed() as u16 - size_of::<crate::zc::SpHeader>() as u16 - 1;
@@ -323,7 +330,7 @@ impl<'slice> PusTc<'slice> {
         self.crc16 = Some(digest.finalize())
     }
 
-    /// This helper function calls both [PusTc.update_ccsds_data_len] and [PusTc.calc_own_crc16]
+    /// This helper function calls both [PusTc::update_ccsds_data_len] and [PusTc::calc_own_crc16].
     pub fn update_packet_fields(&mut self) {
         self.update_ccsds_data_len();
         self.calc_own_crc16();
@@ -332,7 +339,6 @@ impl<'slice> PusTc<'slice> {
     /// Write the raw PUS byte representation to a provided buffer.
     pub fn write_to_bytes(&self, slice: &mut [u8]) -> Result<usize, PusError> {
         let mut curr_idx = 0;
-        let sph_zc = crate::zc::SpHeader::from(self.sp_header);
         let tc_header_len = size_of::<zc::PusTcSecondaryHeader>();
         let total_size = self.len_packed();
         if total_size > slice.len() {
@@ -342,10 +348,7 @@ impl<'slice> PusTc<'slice> {
             })
             .into());
         }
-        sph_zc
-            .to_bytes(&mut slice[curr_idx..curr_idx + CCSDS_HEADER_LEN])
-            .ok_or(ByteConversionError::ZeroCopyToError)?;
-
+        self.sp_header.write_to_be_bytes(slice)?;
         curr_idx += CCSDS_HEADER_LEN;
         let sec_header = zc::PusTcSecondaryHeader::try_from(self.sec_header).unwrap();
         sec_header
@@ -401,18 +404,16 @@ impl<'slice> PusTc<'slice> {
     }
 
     /// Create a [PusTc] instance from a raw slice. On success, it returns a tuple containing
-    /// the instance and the found byte length of the packet
-    pub fn from_bytes(slice: &'slice [u8]) -> Result<(Self, usize), PusError> {
+    /// the instance and the found byte length of the packet.
+    pub fn from_bytes(slice: &'app_data [u8]) -> Result<(Self, usize), PusError> {
         let raw_data_len = slice.len();
         if raw_data_len < PUS_TC_MIN_LEN_WITHOUT_APP_DATA {
             return Err(PusError::RawDataTooShort(raw_data_len));
         }
         let mut current_idx = 0;
-        let sph =
-            crate::zc::SpHeader::from_bytes(&slice[current_idx..current_idx + CCSDS_HEADER_LEN])
-                .ok_or(ByteConversionError::ZeroCopyFromError)?;
+        let (sp_header, _) = SpHeader::from_be_bytes(&slice[0..CCSDS_HEADER_LEN])?;
         current_idx += CCSDS_HEADER_LEN;
-        let total_len = sph.total_len();
+        let total_len = sp_header.total_len();
         if raw_data_len < total_len || total_len < PUS_TC_MIN_LEN_WITHOUT_APP_DATA {
             return Err(PusError::RawDataTooShort(raw_data_len));
         }
@@ -423,7 +424,7 @@ impl<'slice> PusTc<'slice> {
         current_idx += PUC_TC_SECONDARY_HEADER_LEN;
         let raw_data = &slice[0..total_len];
         let pus_tc = PusTc {
-            sp_header: SpHeader::from(sph),
+            sp_header,
             sec_header: PusTcSecondaryHeader::try_from(sec_header).unwrap(),
             raw_data: Some(raw_data),
             app_data: user_data_from_raw(current_idx, total_len, raw_data_len, slice)?,
@@ -434,7 +435,7 @@ impl<'slice> PusTc<'slice> {
         Ok((pus_tc, total_len))
     }
 
-    pub fn raw(&self) -> Option<&'slice [u8]> {
+    pub fn raw(&self) -> Option<&'app_data [u8]> {
         self.raw_data
     }
 }
@@ -462,7 +463,7 @@ impl PusPacket for PusTc<'_> {
 }
 
 //noinspection RsTraitImplementation
-impl PusTcSecondaryHeaderT for PusTc<'_> {
+impl GenericPusTcSecondaryHeader for PusTc<'_> {
     delegate!(to self.sec_header {
         fn pus_version(&self) -> PusVersion;
         fn service(&self) -> u8;
@@ -472,29 +473,29 @@ impl PusTcSecondaryHeaderT for PusTc<'_> {
     });
 }
 
-#[cfg(test)]
+#[cfg(all(test, feature = "std"))]
 mod tests {
     use crate::ecss::PusVersion::PusC;
     use crate::ecss::{PusError, PusPacket};
     use crate::tc::ACK_ALL;
-    use crate::tc::{PusTc, PusTcSecondaryHeader, PusTcSecondaryHeaderT};
+    use crate::tc::{GenericPusTcSecondaryHeader, PusTc, PusTcSecondaryHeader};
     use crate::{ByteConversionError, SpHeader};
     use crate::{CcsdsPacket, SequenceFlags};
     use alloc::vec::Vec;
 
     fn base_ping_tc_full_ctor() -> PusTc<'static> {
-        let mut sph = SpHeader::tc(0x02, 0x34, 0).unwrap();
+        let mut sph = SpHeader::tc_unseg(0x02, 0x34, 0).unwrap();
         let tc_header = PusTcSecondaryHeader::new_simple(17, 1);
         PusTc::new(&mut sph, tc_header, None, true)
     }
 
     fn base_ping_tc_simple_ctor() -> PusTc<'static> {
-        let mut sph = SpHeader::tc(0x02, 0x34, 0).unwrap();
+        let mut sph = SpHeader::tc_unseg(0x02, 0x34, 0).unwrap();
         PusTc::new_simple(&mut sph, 17, 1, None, true)
     }
 
     fn base_ping_tc_simple_ctor_with_app_data(app_data: &'static [u8]) -> PusTc<'static> {
-        let mut sph = SpHeader::tc(0x02, 0x34, 0).unwrap();
+        let mut sph = SpHeader::tc_unseg(0x02, 0x34, 0).unwrap();
         PusTc::new_simple(&mut sph, 17, 1, Some(app_data), true)
     }
 
@@ -534,7 +535,7 @@ mod tests {
 
     #[test]
     fn test_update_func() {
-        let mut sph = SpHeader::tc(0x02, 0x34, 0).unwrap();
+        let mut sph = SpHeader::tc_unseg(0x02, 0x34, 0).unwrap();
         let mut tc = PusTc::new_simple(&mut sph, 17, 1, None, false);
         tc.calc_crc_on_serialization = false;
         assert_eq!(tc.data_len(), 0);
@@ -560,7 +561,6 @@ mod tests {
     }
 
     #[test]
-    #[cfg(feature = "alloc")]
     fn test_vec_ser_deser() {
         let pus_tc = base_ping_tc_simple_ctor();
         let mut test_vec = Vec::new();
@@ -625,7 +625,7 @@ mod tests {
     }
 
     #[test]
-    fn test_write_buf_too_msall() {
+    fn test_write_buf_too_small() {
         let pus_tc = base_ping_tc_simple_ctor();
         let mut test_buf = [0; 12];
         let res = pus_tc.write_to_bytes(test_buf.as_mut_slice());
@@ -698,7 +698,7 @@ mod tests {
         assert_eq!(tc.apid(), 0x02);
         assert_eq!(tc.ack_flags(), ACK_ALL);
         assert_eq!(tc.len_packed(), exp_full_len);
-        let mut comp_header = SpHeader::tc(0x02, 0x34, exp_full_len as u16 - 7).unwrap();
+        let mut comp_header = SpHeader::tc_unseg(0x02, 0x34, exp_full_len as u16 - 7).unwrap();
         comp_header.set_sec_header_flag();
         assert_eq!(tc.sp_header, comp_header);
     }

src/time.rs

@@ -1,469 +0,0 @@
-//! CCSDS Time Code Formats according to [CCSDS 301.0-B-4](https://public.ccsds.org/Pubs/301x0b4e1.pdf)
-use crate::{ByteConversionError, SizeMissmatch};
-use chrono::{DateTime, LocalResult, TimeZone, Utc};
-
-#[allow(unused_imports)]
-#[cfg(not(feature = "std"))]
-use num_traits::float::FloatCore;
-
-use crate::time::CcsdsTimeCodes::Cds;
-#[cfg(feature = "std")]
-use std::time::{SystemTime, SystemTimeError};
-
-pub const CDS_SHORT_LEN: usize = 7;
-pub const DAYS_CCSDS_TO_UNIX: i32 = -4383;
-pub const SECONDS_PER_DAY: u32 = 86400;
-
-#[derive(Debug, PartialEq, Eq, Copy, Clone)]
-pub enum CcsdsTimeCodes {
-    None = 0,
-    CucCcsdsEpoch = 0b001,
-    CucAgencyEpoch = 0b010,
-    Cds = 0b100,
-    Ccs = 0b101,
-}
-
-const CDS_SHORT_P_FIELD: u8 = (CcsdsTimeCodes::Cds as u8) << 4;
-
-impl TryFrom<u8> for CcsdsTimeCodes {
-    type Error = ();
-
-    fn try_from(value: u8) -> Result<Self, Self::Error> {
-        match value {
-            x if x == CcsdsTimeCodes::None as u8 => Ok(CcsdsTimeCodes::None),
-            x if x == CcsdsTimeCodes::CucCcsdsEpoch as u8 => Ok(CcsdsTimeCodes::CucCcsdsEpoch),
-            x if x == CcsdsTimeCodes::CucAgencyEpoch as u8 => Ok(CcsdsTimeCodes::CucAgencyEpoch),
-            x if x == CcsdsTimeCodes::Cds as u8 => Ok(CcsdsTimeCodes::Cds),
-            x if x == CcsdsTimeCodes::Ccs as u8 => Ok(CcsdsTimeCodes::Ccs),
-            _ => Err(()),
-        }
-    }
-}
-
-#[derive(Debug, PartialEq, Eq, Copy, Clone)]
-pub enum TimestampError {
-    /// Contains tuple where first value is the expected time code and the second
-    /// value is the found raw value
-    InvalidTimeCode(CcsdsTimeCodes, u8),
-    OtherPacketError(ByteConversionError),
-}
-
-#[cfg(feature = "std")]
-#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
-pub fn seconds_since_epoch() -> f64 {
-    SystemTime::now()
-        .duration_since(SystemTime::UNIX_EPOCH)
-        .expect("System time generation failed")
-        .as_secs_f64()
-}
-
-/// Convert UNIX days to CCSDS days
-///
-///  - CCSDS epoch: 1958 January 1
-///  - UNIX Epoch: 1970 January 1
-pub const fn unix_to_ccsds_days(unix_days: i32) -> i32 {
-    unix_days - DAYS_CCSDS_TO_UNIX
-}
-
-/// Convert CCSDS days to UNIX days
-///
-///  - CCSDS epoch: 1958 January 1
-///  - UNIX Epoch: 1970 January 1
-pub const fn ccsds_to_unix_days(ccsds_days: i32) -> i32 {
-    ccsds_days + DAYS_CCSDS_TO_UNIX
-}
-
-pub trait TimeWriter {
-    fn write_to_bytes(&self, bytes: &mut [u8]) -> Result<(), TimestampError>;
-}
-
-pub trait TimeReader {
-    fn from_bytes(buf: &[u8]) -> Result<Self, TimestampError>
-    where
-        Self: Sized;
-}
-
-/// Trait for generic CCSDS time providers
-pub trait CcsdsTimeProvider {
-    fn len_as_bytes(&self) -> usize;
-
-    /// Returns the pfield of the time provider. The pfield can have one or two bytes depending
-    /// on the extension bit (first bit). The time provider should returns a tuple where the first
-    /// entry denotes the length of the pfield and the second entry is the value of the pfield
-    /// in big endian format.
-    fn p_field(&self) -> (usize, [u8; 2]);
-    fn ccdsd_time_code(&self) -> CcsdsTimeCodes;
-    fn unix_seconds(&self) -> i64;
-    fn date_time(&self) -> Option<DateTime<Utc>>;
-}
-
-/// This object is the abstraction for the CCSDS Day Segmented Time Code (CDS).
-///
-/// It has the capability to generate and read timestamps as specified in the CCSDS 301.0-B-4
-/// section 3.3
-///
-/// # Example
-///
-/// ```
-/// use spacepackets::time::{CdsShortTimeProvider, TimeWriter};
-/// use spacepackets::time::CcsdsTimeCodes::Cds;
-/// let timestamp_now = CdsShortTimeProvider::from_now().unwrap();
-/// let mut raw_stamp = [0; 7];
-/// timestamp_now.write_to_bytes(&mut raw_stamp).unwrap();
-/// assert_eq!((raw_stamp[0] >> 4) & 0b111, Cds as u8);
-/// ```
-#[derive(Debug, Copy, Clone, Default)]
-pub struct CdsShortTimeProvider {
-    ccsds_days: u16,
-    ms_of_day: u32,
-    unix_seconds: i64,
-    date_time: Option<DateTime<Utc>>,
-}
-
-impl CdsShortTimeProvider {
-    pub fn new(ccsds_days: u16, ms_of_day: u32) -> Self {
-        let provider = Self {
-            ccsds_days,
-            ms_of_day,
-            unix_seconds: 0,
-            date_time: None,
-        };
-        let unix_days_seconds =
-            ccsds_to_unix_days(ccsds_days as i32) as i64 * SECONDS_PER_DAY as i64;
-        provider.setup(unix_days_seconds as i64, ms_of_day.into())
-    }
-
-    #[cfg(feature = "std")]
-    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
-    pub fn from_now() -> Result<Self, SystemTimeError> {
-        let now = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH)?;
-        let epoch = now.as_secs();
-        let secs_of_day = epoch % SECONDS_PER_DAY as u64;
-        let unix_days_seconds = epoch - secs_of_day;
-        let ms_of_day = secs_of_day * 1000 + now.subsec_millis() as u64;
-        let provider = Self {
-            ccsds_days: unix_to_ccsds_days((unix_days_seconds / SECONDS_PER_DAY as u64) as i32)
-                as u16,
-            ms_of_day: ms_of_day as u32,
-            unix_seconds: 0,
-            date_time: None,
-        };
-        Ok(provider.setup(unix_days_seconds as i64, ms_of_day))
-    }
-
-    #[cfg(feature = "std")]
-    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
-    pub fn update_from_now(&mut self) -> Result<(), SystemTimeError> {
-        let now = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH)?;
-        let epoch = now.as_secs();
-        let secs_of_day = epoch % SECONDS_PER_DAY as u64;
-        let unix_days_seconds = epoch - secs_of_day;
-        let ms_of_day = secs_of_day * 1000 + now.subsec_millis() as u64;
-        self.setup(unix_days_seconds as i64, ms_of_day);
-        Ok(())
-    }
-
-    fn setup(mut self, unix_days_seconds: i64, ms_of_day: u64) -> Self {
-        self.calc_unix_seconds(unix_days_seconds, ms_of_day);
-        self.calc_date_time((ms_of_day % 1000) as u32);
-        self
-    }
-
-    #[cfg(feature = "std")]
-    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
-    pub fn ms_of_day_using_sysclock() -> u32 {
-        Self::ms_of_day(seconds_since_epoch())
-    }
-
-    pub fn ms_of_day(seconds_since_epoch: f64) -> u32 {
-        let fraction_ms = seconds_since_epoch - seconds_since_epoch.floor();
-        let ms_of_day: u32 =
-            (((seconds_since_epoch.floor() as u32 % SECONDS_PER_DAY) * 1000) as f64 + fraction_ms)
-                .floor() as u32;
-        ms_of_day
-    }
-
-    fn calc_unix_seconds(&mut self, unix_days_seconds: i64, ms_of_day: u64) {
-        self.unix_seconds = unix_days_seconds;
-        let seconds_of_day = (ms_of_day / 1000) as i64;
-        if self.unix_seconds < 0 {
-            self.unix_seconds -= seconds_of_day;
-        } else {
-            self.unix_seconds += seconds_of_day;
-        }
-    }
-
-    fn calc_date_time(&mut self, ms_since_last_second: u32) {
-        assert!(ms_since_last_second < 1000, "Invalid MS since last second");
-        let ns_since_last_sec = ms_since_last_second * 1e6 as u32;
-        if let LocalResult::Single(val) = Utc.timestamp_opt(self.unix_seconds, ns_since_last_sec) {
-            self.date_time = Some(val);
-        } else {
-            self.date_time = None;
-        }
-    }
-}
-
-impl CcsdsTimeProvider for CdsShortTimeProvider {
-    fn len_as_bytes(&self) -> usize {
-        CDS_SHORT_LEN
-    }
-
-    fn p_field(&self) -> (usize, [u8; 2]) {
-        (1, [CDS_SHORT_P_FIELD, 0])
-    }
-
-    fn ccdsd_time_code(&self) -> CcsdsTimeCodes {
-        Cds
-    }
-
-    fn unix_seconds(&self) -> i64 {
-        self.unix_seconds
-    }
-
-    fn date_time(&self) -> Option<DateTime<Utc>> {
-        self.date_time
-    }
-}
-
-impl TimeWriter for CdsShortTimeProvider {
-    fn write_to_bytes(&self, buf: &mut [u8]) -> Result<(), TimestampError> {
-        if buf.len() < self.len_as_bytes() {
-            return Err(TimestampError::OtherPacketError(
-                ByteConversionError::ToSliceTooSmall(SizeMissmatch {
-                    expected: self.len_as_bytes(),
-                    found: buf.len(),
-                }),
-            ));
-        }
-        buf[0] = CDS_SHORT_P_FIELD;
-        buf[1..3].copy_from_slice(self.ccsds_days.to_be_bytes().as_slice());
-        buf[3..7].copy_from_slice(self.ms_of_day.to_be_bytes().as_slice());
-        Ok(())
-    }
-}
-
-impl TimeReader for CdsShortTimeProvider {
-    fn from_bytes(buf: &[u8]) -> Result<Self, TimestampError> {
-        if buf.len() < CDS_SHORT_LEN {
-            return Err(TimestampError::OtherPacketError(
-                ByteConversionError::FromSliceTooSmall(SizeMissmatch {
-                    expected: CDS_SHORT_LEN,
-                    found: buf.len(),
-                }),
-            ));
-        }
-        let pfield = buf[0];
-        match CcsdsTimeCodes::try_from(pfield >> 4 & 0b111) {
-            Ok(cds_type) => match cds_type {
-                Cds => (),
-                _ => return Err(TimestampError::InvalidTimeCode(Cds, cds_type as u8)),
-            },
-            _ => return Err(TimestampError::InvalidTimeCode(Cds, pfield >> 4 & 0b111)),
-        };
-        let ccsds_days: u16 = u16::from_be_bytes(buf[1..3].try_into().unwrap());
-        let ms_of_day: u32 = u32::from_be_bytes(buf[3..7].try_into().unwrap());
-        Ok(Self::new(ccsds_days, ms_of_day))
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use crate::time::TimestampError::{InvalidTimeCode, OtherPacketError};
-    use crate::ByteConversionError::{FromSliceTooSmall, ToSliceTooSmall};
-    use alloc::format;
-    use chrono::{Datelike, Timelike};
-
-    #[test]
-    fn test_creation() {
-        assert_eq!(unix_to_ccsds_days(DAYS_CCSDS_TO_UNIX), 0);
-        assert_eq!(ccsds_to_unix_days(0), DAYS_CCSDS_TO_UNIX);
-    }
-
-    #[cfg(feature = "std")]
-    #[test]
-    fn test_get_current_time() {
-        let sec_floats = seconds_since_epoch();
-        assert!(sec_floats > 0.0);
-    }
-
-    #[test]
-    fn test_time_stamp_zero_args() {
-        let time_stamper = CdsShortTimeProvider::new(0, 0);
-        assert_eq!(
-            time_stamper.unix_seconds(),
-            (DAYS_CCSDS_TO_UNIX * SECONDS_PER_DAY as i32) as i64
-        );
-        assert_eq!(time_stamper.ccdsd_time_code(), Cds);
-        assert_eq!(time_stamper.p_field(), (1, [(Cds as u8) << 4, 0]));
-        let date_time = time_stamper.date_time().unwrap();
-        assert_eq!(date_time.year(), 1958);
-        assert_eq!(date_time.month(), 1);
-        assert_eq!(date_time.day(), 1);
-        assert_eq!(date_time.hour(), 0);
-        assert_eq!(date_time.minute(), 0);
-        assert_eq!(date_time.second(), 0);
-    }
-
-    #[test]
-    fn test_time_stamp_unix_epoch() {
-        let time_stamper = CdsShortTimeProvider::new((-DAYS_CCSDS_TO_UNIX) as u16, 0);
-        assert_eq!(time_stamper.unix_seconds(), 0);
-        let date_time = time_stamper.date_time().unwrap();
-        assert_eq!(date_time.year(), 1970);
-        assert_eq!(date_time.month(), 1);
-        assert_eq!(date_time.day(), 1);
-        assert_eq!(date_time.hour(), 0);
-        assert_eq!(date_time.minute(), 0);
-        assert_eq!(date_time.second(), 0);
-    }
-
-    #[test]
-    fn test_write() {
-        let mut buf = [0; 16];
-        let time_stamper_0 = CdsShortTimeProvider::new(0, 0);
-        let mut res = time_stamper_0.write_to_bytes(&mut buf);
-        assert!(res.is_ok());
-        assert_eq!(buf[0], (CcsdsTimeCodes::Cds as u8) << 4);
-        assert_eq!(
-            u16::from_be_bytes(buf[1..3].try_into().expect("Byte conversion failed")),
-            0
-        );
-        assert_eq!(
-            u32::from_be_bytes(buf[3..7].try_into().expect("Byte conversion failed")),
-            0
-        );
-        let time_stamper_1 = CdsShortTimeProvider::new(u16::MAX - 1, u32::MAX - 1);
-        res = time_stamper_1.write_to_bytes(&mut buf);
-        assert!(res.is_ok());
-        assert_eq!(buf[0], (CcsdsTimeCodes::Cds as u8) << 4);
-        assert_eq!(
-            u16::from_be_bytes(buf[1..3].try_into().expect("Byte conversion failed")),
-            u16::MAX - 1
-        );
-        assert_eq!(
-            u32::from_be_bytes(buf[3..7].try_into().expect("Byte conversion failed")),
-            u32::MAX - 1
-        );
-    }
-
-    #[test]
-    fn test_faulty_write_buf_too_small() {
-        let mut buf = [0; 7];
-        let time_stamper = CdsShortTimeProvider::new(u16::MAX - 1, u32::MAX - 1);
-        for i in 0..6 {
-            let res = time_stamper.write_to_bytes(&mut buf[0..i]);
-            assert!(res.is_err());
-            match res.unwrap_err() {
-                OtherPacketError(ToSliceTooSmall(missmatch)) => {
-                    assert_eq!(missmatch.found, i);
-                    assert_eq!(missmatch.expected, 7);
-                }
-                _ => panic!(
-                    "{}",
-                    format!("Invalid error {:?} detected", res.unwrap_err())
-                ),
-            }
-        }
-    }
-
-    #[test]
-    fn test_faulty_read_buf_too_small() {
-        let buf = [0; 7];
-        for i in 0..6 {
-            let res = CdsShortTimeProvider::from_bytes(&buf[0..i]);
-            assert!(res.is_err());
-            match res.unwrap_err() {
-                InvalidTimeCode(_, _) => {
-                    panic!("Unexpected error");
-                }
-                OtherPacketError(e) => match e {
-                    FromSliceTooSmall(missmatch) => {
-                        assert_eq!(missmatch.found, i);
-                        assert_eq!(missmatch.expected, 7);
-                    }
-                    _ => panic!("{}", format!("Invalid error {:?} detected", e)),
-                },
-            }
-        }
-    }
-
-    #[test]
-    fn test_faulty_invalid_pfield() {
-        let mut buf = [0; 16];
-        let time_stamper_0 = CdsShortTimeProvider::new(0, 0);
-        let res = time_stamper_0.write_to_bytes(&mut buf);
-        assert!(res.is_ok());
-        buf[0] = 0;
-        let res = CdsShortTimeProvider::from_bytes(&buf);
-        assert!(res.is_err());
-        let err = res.unwrap_err();
-        match err {
-            InvalidTimeCode(code, raw) => {
-                assert_eq!(code, Cds);
-                assert_eq!(raw, 0);
-            }
-            OtherPacketError(_) => {}
-        }
-    }
-
-    #[test]
-    fn test_reading() {
-        let mut buf = [0; 16];
-        let time_stamper = CdsShortTimeProvider::new(u16::MAX - 1, u32::MAX - 1);
-        let res = time_stamper.write_to_bytes(&mut buf);
-        assert!(res.is_ok());
-        assert_eq!(buf[0], (CcsdsTimeCodes::Cds as u8) << 4);
-        assert_eq!(
-            u16::from_be_bytes(buf[1..3].try_into().expect("Byte conversion failed")),
-            u16::MAX - 1
-        );
-        assert_eq!(
-            u32::from_be_bytes(buf[3..7].try_into().expect("Byte conversion failed")),
-            u32::MAX - 1
-        );
-
-        let read_stamp = CdsShortTimeProvider::from_bytes(&buf).expect("Reading timestamp failed");
-        assert_eq!(read_stamp.ccsds_days, u16::MAX - 1);
-        assert_eq!(read_stamp.ms_of_day, u32::MAX - 1);
-    }
-
-    #[cfg(feature = "std")]
-    #[test]
-    fn test_time_now() {
-        let timestamp_now = CdsShortTimeProvider::from_now().unwrap();
-        let compare_stamp = Utc::now();
-        let dt = timestamp_now.date_time().unwrap();
-        if compare_stamp.year() > dt.year() {
-            assert_eq!(compare_stamp.year() - dt.year(), 1);
-        } else {
-            assert_eq!(dt.year(), compare_stamp.year());
-        }
-        generic_dt_property_equality_check(dt.month(), compare_stamp.month(), 1, 12);
-
-        assert_eq!(dt.day(), compare_stamp.day());
-        if compare_stamp.day() < dt.day() {
-            assert!(dt.day() >= 28);
-            assert_eq!(compare_stamp.day(), 1);
-        } else if compare_stamp.day() > dt.day() {
-            assert_eq!(compare_stamp.day() - dt.day(), 1);
-        } else {
-            assert_eq!(compare_stamp.day(), dt.day());
-        }
-        generic_dt_property_equality_check(dt.hour(), compare_stamp.hour(), 0, 23);
-        generic_dt_property_equality_check(dt.minute(), compare_stamp.minute(), 0, 59);
-    }
-
-    #[cfg(feature = "std")]
-    fn generic_dt_property_equality_check(first: u32, second: u32, start: u32, end: u32) {
-        if second < first {
-            assert_eq!(second, start);
-            assert_eq!(first, end);
-        } else if second > first {
-            assert_eq!(second - first, 1);
-        } else {
-            assert_eq!(first, second);
-        }
-    }
-}

src/time/ascii.rs

@@ -0,0 +1,130 @@
+//! Module to generate the ASCII timecodes specified in
+//! [CCSDS 301.0-B-4](https://public.ccsds.org/Pubs/301x0b4e1.pdf) section 3.5 .
+//! See [chrono::DateTime::format] for a usage example of the generated
+//! [chrono::format::DelayedFormat] structs.
+#[cfg(feature = "alloc")]
+use chrono::{
+    format::{DelayedFormat, StrftimeItems},
+    DateTime, Utc,
+};
+
+/// Tuple of format string and formatted size for time code A.
+///
+/// Format: YYYY-MM-DDThh:mm:ss.ddd
+///
+/// Three digits are used for the decimal fraction
+pub const FMT_STR_CODE_A_WITH_SIZE: (&str, usize) = ("%FT%T%.3f", 23);
+/// Tuple of format string and formatted size for time code A.
+///
+///  Format: YYYY-MM-DDThh:mm:ss.dddZ
+///
+/// Three digits are used for the decimal fraction and a terminator is added at the end.
+pub const FMT_STR_CODE_A_TERMINATED_WITH_SIZE: (&str, usize) = ("%FT%T%.3fZ", 24);
+
+/// Tuple of format string and formatted size for time code A.
+///
+/// Format: YYYY-DDDThh:mm:ss.ddd
+///
+/// Three digits are used for the decimal fraction
+pub const FMT_STR_CODE_B_WITH_SIZE: (&str, usize) = ("%Y-%jT%T%.3f", 21);
+/// Tuple of format string and formatted size for time code A.
+///
+/// Format: YYYY-DDDThh:mm:ss.dddZ
+///
+/// Three digits are used for the decimal fraction and a terminator is added at the end.
+pub const FMT_STR_CODE_B_TERMINATED_WITH_SIZE: (&str, usize) = ("%Y-%jT%T%.3fZ", 22);
+
+/// Generates a time code formatter using the [FMT_STR_CODE_A_WITH_SIZE] format.
+#[cfg(feature = "alloc")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "alloc")))]
+pub fn generate_time_code_a(date: &DateTime<Utc>) -> DelayedFormat<StrftimeItems<'static>> {
+    date.format(FMT_STR_CODE_A_WITH_SIZE.0)
+}
+
+/// Generates a time code formatter using the [FMT_STR_CODE_A_TERMINATED_WITH_SIZE] format.
+#[cfg(feature = "alloc")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "alloc")))]
+pub fn generate_time_code_a_terminated(
+    date: &DateTime<Utc>,
+) -> DelayedFormat<StrftimeItems<'static>> {
+    date.format(FMT_STR_CODE_A_TERMINATED_WITH_SIZE.0)
+}
+
+/// Generates a time code formatter using the [FMT_STR_CODE_B_WITH_SIZE] format.
+#[cfg(feature = "alloc")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "alloc")))]
+pub fn generate_time_code_b(date: &DateTime<Utc>) -> DelayedFormat<StrftimeItems<'static>> {
+    date.format(FMT_STR_CODE_B_WITH_SIZE.0)
+}
+
+/// Generates a time code formatter using the [FMT_STR_CODE_B_TERMINATED_WITH_SIZE] format.
+#[cfg(feature = "alloc")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "alloc")))]
+pub fn generate_time_code_b_terminated(
+    date: &DateTime<Utc>,
+) -> DelayedFormat<StrftimeItems<'static>> {
+    date.format(FMT_STR_CODE_B_TERMINATED_WITH_SIZE.0)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use chrono::Utc;
+    use std::format;
+
+    #[test]
+    fn test_ascii_timestamp_a_unterminated() {
+        let date = Utc::now();
+        let stamp_formatter = generate_time_code_a(&date);
+        let stamp = format!("{}", stamp_formatter);
+        let t_sep = stamp.find("T");
+        assert!(t_sep.is_some());
+        assert_eq!(t_sep.unwrap(), 10);
+        assert_eq!(stamp.len(), FMT_STR_CODE_A_WITH_SIZE.1);
+    }
+
+    #[test]
+    fn test_ascii_timestamp_a_terminated() {
+        let date = Utc::now();
+        let stamp_formatter = generate_time_code_a_terminated(&date);
+        let stamp = format!("{}", stamp_formatter);
+        let t_sep = stamp.find("T");
+        assert!(t_sep.is_some());
+        assert_eq!(t_sep.unwrap(), 10);
+        let z_terminator = stamp.find("Z");
+        assert!(z_terminator.is_some());
+        assert_eq!(
+            z_terminator.unwrap(),
+            FMT_STR_CODE_A_TERMINATED_WITH_SIZE.1 - 1
+        );
+        assert_eq!(stamp.len(), FMT_STR_CODE_A_TERMINATED_WITH_SIZE.1);
+    }
+
+    #[test]
+    fn test_ascii_timestamp_b_unterminated() {
+        let date = Utc::now();
+        let stamp_formatter = generate_time_code_b(&date);
+        let stamp = format!("{}", stamp_formatter);
+        let t_sep = stamp.find("T");
+        assert!(t_sep.is_some());
+        assert_eq!(t_sep.unwrap(), 8);
+        assert_eq!(stamp.len(), FMT_STR_CODE_B_WITH_SIZE.1);
+    }
+
+    #[test]
+    fn test_ascii_timestamp_b_terminated() {
+        let date = Utc::now();
+        let stamp_formatter = generate_time_code_b_terminated(&date);
+        let stamp = format!("{}", stamp_formatter);
+        let t_sep = stamp.find("T");
+        assert!(t_sep.is_some());
+        assert_eq!(t_sep.unwrap(), 8);
+        let z_terminator = stamp.find("Z");
+        assert!(z_terminator.is_some());
+        assert_eq!(
+            z_terminator.unwrap(),
+            FMT_STR_CODE_B_TERMINATED_WITH_SIZE.1 - 1
+        );
+        assert_eq!(stamp.len(), FMT_STR_CODE_B_TERMINATED_WITH_SIZE.1);
+    }
+}

src/time/cds.rs

@@ -0,0 +1,956 @@
+//! Module to generate or read CCSDS Day Segmented (CDS) timestamps as specified in
+//! [CCSDS 301.0-B-4](https://public.ccsds.org/Pubs/301x0b4e1.pdf) section 3.3 .
+//!
+//! The core data structure to do this is the [cds::TimeProvider] struct.
+use super::*;
+use crate::private::Sealed;
+use core::fmt::Debug;
+
+/// Base value for the preamble field for a time field parser to determine the time field type.
+pub const P_FIELD_BASE: u8 = (CcsdsTimeCodes::Cds as u8) << 4;
+pub const MIN_CDS_FIELD_LEN: usize = 7;
+
+/// Generic trait implemented by token structs to specify the length of day field at type
+/// level. This trait is only meant to be implemented in this crate and therefore sealed.
+pub trait ProvidesDaysLength: Sealed {
+    type FieldType: Copy + Clone + TryFrom<i32>;
+}
+
+/// Type level token to be used as a generic parameter to [TimeProvider].
+#[derive(Debug, PartialEq, Eq, Default)]
+pub struct DaysLen16Bits {}
+
+impl Sealed for DaysLen16Bits {}
+impl ProvidesDaysLength for DaysLen16Bits {
+    type FieldType = u16;
+}
+
+/// Type level token to be used as a generic parameter to [TimeProvider].
+#[derive(Debug, PartialEq, Eq, Default)]
+pub struct DaysLen24Bits {}
+impl Sealed for DaysLen24Bits {}
+impl ProvidesDaysLength for DaysLen24Bits {
+    type FieldType = u32;
+}
+
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub enum LengthOfDaySegment {
+    Short16Bits = 0,
+    Long24Bits = 1,
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub enum SubmillisPrecision {
+    Absent,
+    Microseconds(u16),
+    Picoseconds(u32),
+    Reserved,
+}
+
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub enum CdsError {
+    /// CCSDS days value exceeds maximum allowed size or is negative
+    InvalidCcsdsDays(i64),
+    /// There are distinct constructors depending on the days field width detected in the preamble
+    /// field. This error will be returned if there is a missmatch.
+    InvalidCtorForDaysOfLenInPreamble(LengthOfDaySegment),
+}
+
+impl Display for CdsError {
+    fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
+        match self {
+            CdsError::InvalidCcsdsDays(days) => {
+                write!(f, "invalid ccsds days {}", days)
+            }
+            CdsError::InvalidCtorForDaysOfLenInPreamble(length_of_day) => {
+                write!(
+                    f,
+                    "wrong constructor for length of day {:?} detected in preamble",
+                    length_of_day
+                )
+            }
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl Error for CdsError {}
+pub fn length_of_day_segment_from_pfield(pfield: u8) -> LengthOfDaySegment {
+    if (pfield >> 2) & 0b1 == 1 {
+        return LengthOfDaySegment::Long24Bits;
+    }
+    LengthOfDaySegment::Short16Bits
+}
+pub fn precision_from_pfield(pfield: u8) -> SubmillisPrecision {
+    match pfield & 0b11 {
+        0b01 => SubmillisPrecision::Microseconds(0),
+        0b10 => SubmillisPrecision::Picoseconds(0),
+        0b00 => SubmillisPrecision::Absent,
+        0b11 => SubmillisPrecision::Reserved,
+        _ => panic!("pfield to SubmillisPrecision failed"),
+    }
+}
+
+/// This object is the abstraction for the CCSDS Day Segmented Time Code (CDS).
+///
+/// It has the capability to generate and read timestamps as specified in the CCSDS 301.0-B-4
+/// section 3.3 . The width of the days field is configured at compile time via the generic
+/// [ProvidesDaysLength] trait which is implemented by [DaysLen16Bits] and [DaysLen24Bits].
+///
+/// Custom epochs are not supported yet.
+/// Furthermore, the preamble field (p-field) is explicitly conveyed.
+/// That means it will always be present when writing the time stamp to a raw buffer, and it
+/// must be present when reading a CDS timestamp from a raw buffer.
+///
+/// # Example
+///
+/// ```
+/// use spacepackets::time::cds::{TimeProvider, DaysLen16Bits};
+/// use spacepackets::time::{TimeWriter, CcsdsTimeCodes, TimeReader, CcsdsTimeProvider};
+///
+/// let timestamp_now = TimeProvider::from_now_with_u16_days().unwrap();
+/// let mut raw_stamp = [0; 7];
+/// {
+///     let written = timestamp_now.write_to_bytes(&mut raw_stamp).unwrap();
+///     assert_eq!((raw_stamp[0] >> 4) & 0b111, CcsdsTimeCodes::Cds as u8);
+///     assert_eq!(written, 7);
+/// }
+/// {
+///     let read_result = TimeProvider::<DaysLen16Bits>::from_bytes(&raw_stamp);
+///     assert!(read_result.is_ok());
+///     let stamp_deserialized = read_result.unwrap();
+///     assert_eq!(stamp_deserialized.len_as_bytes(), 7);
+/// }
+/// ```
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub struct TimeProvider<DaysLen: ProvidesDaysLength = DaysLen16Bits> {
+    pfield: u8,
+    ccsds_days: DaysLen::FieldType,
+    ms_of_day: u32,
+    submillis_precision: Option<SubmillisPrecision>,
+    unix_seconds: i64,
+}
+
+#[cfg(feature = "std")]
+struct ConversionFromNow {
+    ccsds_days: i32,
+    ms_of_day: u64,
+    unix_days_seconds: u64,
+    submillis_prec: Option<SubmillisPrecision>,
+}
+
+#[cfg(feature = "std")]
+impl ConversionFromNow {
+    fn new() -> Result<Self, SystemTimeError> {
+        Self::new_generic(None)
+    }
+
+    fn new_with_submillis_us_prec() -> Result<Self, SystemTimeError> {
+        Self::new_generic(Some(SubmillisPrecision::Microseconds(0)))
+    }
+
+    fn new_with_submillis_ps_prec() -> Result<Self, SystemTimeError> {
+        Self::new_generic(Some(SubmillisPrecision::Picoseconds(0)))
+    }
+
+    fn new_generic(mut prec: Option<SubmillisPrecision>) -> Result<Self, SystemTimeError> {
+        let now = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH)?;
+        let epoch = now.as_secs();
+        let secs_of_day = epoch % SECONDS_PER_DAY as u64;
+        let unix_days_seconds = epoch - secs_of_day;
+        if let Some(submilli_prec) = prec {
+            match submilli_prec {
+                SubmillisPrecision::Microseconds(_) => {
+                    prec = Some(SubmillisPrecision::Microseconds(
+                        (now.subsec_micros() % 1000) as u16,
+                    ));
+                }
+                SubmillisPrecision::Picoseconds(_) => {
+                    prec = Some(SubmillisPrecision::Picoseconds(
+                        (now.subsec_nanos() % 10_u32.pow(6)) * 1000,
+                    ));
+                }
+                _ => (),
+            }
+        }
+        Ok(Self {
+            ms_of_day: secs_of_day * 1000 + now.subsec_millis() as u64,
+            ccsds_days: unix_to_ccsds_days((unix_days_seconds / SECONDS_PER_DAY as u64) as i64)
+                as i32,
+            unix_days_seconds,
+            submillis_prec: prec,
+        })
+    }
+}
+
+impl<ProvidesDaysLen: ProvidesDaysLength> TimeProvider<ProvidesDaysLen> {
+    pub fn set_submillis_precision(&mut self, prec: SubmillisPrecision) {
+        self.pfield &= !(0b11);
+        if let SubmillisPrecision::Absent = prec {
+            self.submillis_precision = None;
+            return;
+        }
+        self.submillis_precision = Some(prec);
+        match prec {
+            SubmillisPrecision::Microseconds(_) => {
+                self.pfield |= 0b01;
+            }
+            SubmillisPrecision::Picoseconds(_) => {
+                self.pfield |= 0b10;
+            }
+            _ => (),
+        }
+    }
+
+    pub fn clear_submillis_precision(&mut self) {
+        self.pfield &= !(0b11);
+        self.submillis_precision = None;
+    }
+
+    pub fn ccsds_days(&self) -> ProvidesDaysLen::FieldType {
+        self.ccsds_days
+    }
+
+    pub fn submillis_precision(&self) -> Option<SubmillisPrecision> {
+        self.submillis_precision
+    }
+
+    pub fn ms_of_day(&self) -> u32 {
+        self.ms_of_day
+    }
+
+    fn generic_raw_read_checks(
+        buf: &[u8],
+        days_len: LengthOfDaySegment,
+    ) -> Result<SubmillisPrecision, TimestampError> {
+        if buf.len() < MIN_CDS_FIELD_LEN {
+            return Err(TimestampError::ByteConversionError(
+                ByteConversionError::FromSliceTooSmall(SizeMissmatch {
+                    expected: MIN_CDS_FIELD_LEN,
+                    found: buf.len(),
+                }),
+            ));
+        }
+        let pfield = buf[0];
+        match CcsdsTimeCodes::try_from(pfield >> 4 & 0b111) {
+            Ok(cds_type) => match cds_type {
+                CcsdsTimeCodes::Cds => (),
+                _ => {
+                    return Err(TimestampError::InvalidTimeCode(
+                        CcsdsTimeCodes::Cds,
+                        cds_type as u8,
+                    ))
+                }
+            },
+            _ => {
+                return Err(TimestampError::InvalidTimeCode(
+                    CcsdsTimeCodes::Cds,
+                    pfield >> 4 & 0b111,
+                ))
+            }
+        };
+        if ((pfield >> 3) & 0b1) == 1 {
+            return Err(TimestampError::CustomEpochNotSupported);
+        }
+        let days_len_from_pfield = length_of_day_segment_from_pfield(pfield);
+        if days_len_from_pfield != days_len {
+            return Err(CdsError::InvalidCtorForDaysOfLenInPreamble(days_len_from_pfield).into());
+        }
+        let stamp_len = Self::calc_stamp_len(pfield);
+        if buf.len() < stamp_len {
+            return Err(TimestampError::ByteConversionError(
+                ByteConversionError::FromSliceTooSmall(SizeMissmatch {
+                    expected: stamp_len,
+                    found: buf.len(),
+                }),
+            ));
+        }
+        Ok(precision_from_pfield(pfield))
+    }
+
+    fn calc_stamp_len(pfield: u8) -> usize {
+        let mut init_len = 7;
+        if length_of_day_segment_from_pfield(pfield) == LengthOfDaySegment::Long24Bits {
+            init_len += 1
+        }
+        match pfield & 0b11 {
+            0b01 => {
+                init_len += 2;
+            }
+            0b10 => {
+                init_len += 4;
+            }
+            _ => (),
+        }
+        init_len
+    }
+
+    fn setup(&mut self, unix_days_seconds: i64, ms_of_day: u64) {
+        self.calc_unix_seconds(unix_days_seconds, ms_of_day);
+    }
+
+    fn calc_unix_seconds(&mut self, unix_days_seconds: i64, ms_of_day: u64) {
+        self.unix_seconds = unix_days_seconds;
+        let seconds_of_day = (ms_of_day / 1000) as i64;
+        if self.unix_seconds < 0 {
+            self.unix_seconds -= seconds_of_day;
+        } else {
+            self.unix_seconds += seconds_of_day;
+        }
+    }
+
+    fn calc_date_time(&self, ms_since_last_second: u32) -> Option<DateTime<Utc>> {
+        assert!(ms_since_last_second < 1000, "Invalid MS since last second");
+        let ns_since_last_sec = ms_since_last_second * 1e6 as u32;
+        if let LocalResult::Single(val) = Utc.timestamp_opt(self.unix_seconds, ns_since_last_sec) {
+            return Some(val);
+        }
+        None
+    }
+
+    fn length_check(&self, buf: &[u8], len_as_bytes: usize) -> Result<(), TimestampError> {
+        if buf.len() < len_as_bytes {
+            return Err(TimestampError::ByteConversionError(
+                ByteConversionError::ToSliceTooSmall(SizeMissmatch {
+                    expected: len_as_bytes,
+                    found: buf.len(),
+                }),
+            ));
+        }
+        Ok(())
+    }
+
+    fn generic_new(
+        days_len: LengthOfDaySegment,
+        ccsds_days: ProvidesDaysLen::FieldType,
+        ms_of_day: u32,
+    ) -> Result<Self, CdsError>
+    where
+        i64: From<ProvidesDaysLen::FieldType>,
+    {
+        let mut provider = Self {
+            pfield: Self::generate_p_field(days_len, None),
+            ccsds_days,
+            ms_of_day,
+            unix_seconds: 0,
+            submillis_precision: None,
+        };
+        let unix_days_seconds = ccsds_to_unix_days(ccsds_days.into()) * SECONDS_PER_DAY as i64;
+        provider.setup(unix_days_seconds, ms_of_day.into());
+        Ok(provider)
+    }
+
+    #[cfg(feature = "std")]
+    fn generic_from_now(
+        days_len: LengthOfDaySegment,
+        conversion_from_now: ConversionFromNow,
+    ) -> Result<Self, StdTimestampError>
+    where
+        <ProvidesDaysLen::FieldType as TryFrom<i32>>::Error: Debug,
+    {
+        let ccsds_days: ProvidesDaysLen::FieldType =
+            conversion_from_now.ccsds_days.try_into().map_err(|_| {
+                StdTimestampError::TimestampError(
+                    CdsError::InvalidCcsdsDays(conversion_from_now.ccsds_days.into()).into(),
+                )
+            })?;
+        let mut provider = Self {
+            pfield: Self::generate_p_field(days_len, conversion_from_now.submillis_prec),
+            ccsds_days,
+            ms_of_day: conversion_from_now.ms_of_day as u32,
+            unix_seconds: 0,
+            submillis_precision: conversion_from_now.submillis_prec,
+        };
+        provider.setup(
+            conversion_from_now.unix_days_seconds as i64,
+            conversion_from_now.ms_of_day,
+        );
+        Ok(provider)
+    }
+
+    #[cfg(feature = "std")]
+    fn generic_conversion_from_now(&self) -> Result<ConversionFromNow, SystemTimeError> {
+        Ok(match self.submillis_precision {
+            None => ConversionFromNow::new()?,
+            Some(prec) => match prec {
+                SubmillisPrecision::Microseconds(_) => {
+                    ConversionFromNow::new_with_submillis_us_prec()?
+                }
+                SubmillisPrecision::Picoseconds(_) => {
+                    ConversionFromNow::new_with_submillis_ps_prec()?
+                }
+                _ => ConversionFromNow::new()?,
+            },
+        })
+    }
+
+    fn generate_p_field(
+        day_seg_len: LengthOfDaySegment,
+        submillis_prec: Option<SubmillisPrecision>,
+    ) -> u8 {
+        let mut pfield = P_FIELD_BASE | ((day_seg_len as u8) << 2);
+        if let Some(submillis_prec) = submillis_prec {
+            match submillis_prec {
+                SubmillisPrecision::Microseconds(_) => pfield |= 0b01,
+                SubmillisPrecision::Picoseconds(_) => pfield |= 0b10,
+                SubmillisPrecision::Reserved => pfield |= 0b11,
+                _ => (),
+            }
+        }
+        pfield
+    }
+
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+    pub fn update_from_now(&mut self) -> Result<(), StdTimestampError>
+    where
+        <ProvidesDaysLen::FieldType as TryFrom<i32>>::Error: Debug,
+    {
+        let conversion_from_now = self.generic_conversion_from_now()?;
+        let ccsds_days: ProvidesDaysLen::FieldType =
+            conversion_from_now.ccsds_days.try_into().map_err(|_| {
+                StdTimestampError::TimestampError(
+                    CdsError::InvalidCcsdsDays(conversion_from_now.ccsds_days as i64).into(),
+                )
+            })?;
+        self.ccsds_days = ccsds_days;
+        self.ms_of_day = conversion_from_now.ms_of_day as u32;
+        self.setup(
+            conversion_from_now.unix_days_seconds as i64,
+            conversion_from_now.ms_of_day,
+        );
+        Ok(())
+    }
+}
+
+impl TimeProvider<DaysLen24Bits> {
+    /// Generate a new timestamp provider with the days field width set to 24 bits
+    pub fn new_with_u24_days(ccsds_days: u32, ms_of_day: u32) -> Result<Self, CdsError> {
+        if ccsds_days > 2_u32.pow(24) {
+            return Err(CdsError::InvalidCcsdsDays(ccsds_days.into()));
+        }
+        Self::generic_new(LengthOfDaySegment::Long24Bits, ccsds_days, ms_of_day)
+    }
+
+    /// Generate a time stamp from the current time using the system clock.
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+    pub fn from_now_with_u24_days() -> Result<Self, StdTimestampError> {
+        let conversion_from_now = ConversionFromNow::new()?;
+        Self::generic_from_now(LengthOfDaySegment::Long24Bits, conversion_from_now)
+    }
+
+    /// Like [Self::from_now_with_u24_days] but with microsecond sub-millisecond precision.
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+    pub fn from_now_with_u24_days_and_us_prec() -> Result<Self, StdTimestampError> {
+        let conversion_from_now = ConversionFromNow::new_with_submillis_us_prec()?;
+        Self::generic_from_now(LengthOfDaySegment::Long24Bits, conversion_from_now)
+    }
+
+    /// Like [Self::from_now_with_u24_days] but with picoseconds sub-millisecond precision.
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+    pub fn from_now_with_u24_days_ps_submillis_prec() -> Result<Self, StdTimestampError> {
+        let conversion_from_now = ConversionFromNow::new_with_submillis_ps_prec()?;
+        Self::generic_from_now(LengthOfDaySegment::Long24Bits, conversion_from_now)
+    }
+
+    fn from_bytes_24_bit_days(buf: &[u8]) -> Result<Self, TimestampError> {
+        let submillis_precision =
+            Self::generic_raw_read_checks(buf, LengthOfDaySegment::Long24Bits)?;
+        let mut temp_buf: [u8; 4] = [0; 4];
+        temp_buf[1..4].copy_from_slice(&buf[1..4]);
+        let cccsds_days: u32 = u32::from_be_bytes(temp_buf);
+        let ms_of_day: u32 = u32::from_be_bytes(buf[4..8].try_into().unwrap());
+        let mut provider = Self::new_with_u24_days(cccsds_days, ms_of_day)?;
+        match submillis_precision {
+            SubmillisPrecision::Microseconds(_) => {
+                provider.set_submillis_precision(SubmillisPrecision::Microseconds(
+                    u16::from_be_bytes(buf[8..10].try_into().unwrap()),
+                ))
+            }
+            SubmillisPrecision::Picoseconds(_) => provider.set_submillis_precision(
+                SubmillisPrecision::Picoseconds(u32::from_be_bytes(buf[8..12].try_into().unwrap())),
+            ),
+            _ => (),
+        }
+        Ok(provider)
+    }
+}
+
+impl TimeProvider<DaysLen16Bits> {
+    /// Generate a new timestamp provider with the days field width set to 16 bits
+    pub fn new_with_u16_days(ccsds_days: u16, ms_of_day: u32) -> Self {
+        // This should never fail, type system ensures CCSDS can not be negative or too large
+        Self::generic_new(LengthOfDaySegment::Short16Bits, ccsds_days, ms_of_day).unwrap()
+    }
+
+    /// Generate a time stamp from the current time using the system clock.
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+    pub fn from_now_with_u16_days() -> Result<Self, StdTimestampError> {
+        let conversion_from_now = ConversionFromNow::new()?;
+        Self::generic_from_now(LengthOfDaySegment::Short16Bits, conversion_from_now)
+    }
+
+    /// Like [Self::from_now_with_u16_days] but with microsecond sub-millisecond precision.
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+    pub fn from_now_with_u16_days_and_us_prec() -> Result<Self, StdTimestampError> {
+        let conversion_from_now = ConversionFromNow::new_with_submillis_us_prec()?;
+        Self::generic_from_now(LengthOfDaySegment::Short16Bits, conversion_from_now)
+    }
+
+    /// Like [Self::from_now_with_u16_days] but with picosecond sub-millisecond precision.
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+    pub fn from_now_with_u16_days_and_ps_prec() -> Result<Self, StdTimestampError> {
+        let conversion_from_now = ConversionFromNow::new_with_submillis_ps_prec()?;
+        Self::generic_from_now(LengthOfDaySegment::Short16Bits, conversion_from_now)
+    }
+
+    fn from_bytes_16_bit_days(buf: &[u8]) -> Result<Self, TimestampError> {
+        let submillis_precision =
+            Self::generic_raw_read_checks(buf, LengthOfDaySegment::Short16Bits)?;
+        let ccsds_days: u16 = u16::from_be_bytes(buf[1..3].try_into().unwrap());
+        let ms_of_day: u32 = u32::from_be_bytes(buf[3..7].try_into().unwrap());
+        let mut provider = Self::new_with_u16_days(ccsds_days, ms_of_day);
+        provider.pfield = buf[0];
+        match submillis_precision {
+            SubmillisPrecision::Microseconds(_) => provider.set_submillis_precision(
+                SubmillisPrecision::Microseconds(u16::from_be_bytes(buf[7..9].try_into().unwrap())),
+            ),
+            SubmillisPrecision::Picoseconds(_) => provider.set_submillis_precision(
+                SubmillisPrecision::Picoseconds(u32::from_be_bytes(buf[7..11].try_into().unwrap())),
+            ),
+            _ => (),
+        }
+        Ok(provider)
+    }
+}
+
+impl<ProvidesDaysLen: ProvidesDaysLength> CcsdsTimeProvider for TimeProvider<ProvidesDaysLen> {
+    fn len_as_bytes(&self) -> usize {
+        Self::calc_stamp_len(self.pfield)
+    }
+
+    fn p_field(&self) -> (usize, [u8; 2]) {
+        (1, [self.pfield, 0])
+    }
+
+    fn ccdsd_time_code(&self) -> CcsdsTimeCodes {
+        CcsdsTimeCodes::Cds
+    }
+
+    fn unix_seconds(&self) -> i64 {
+        self.unix_seconds
+    }
+
+    fn date_time(&self) -> Option<DateTime<Utc>> {
+        self.calc_date_time(self.ms_of_day % 1000)
+    }
+}
+
+impl TimeReader for TimeProvider<DaysLen16Bits> {
+    fn from_bytes(buf: &[u8]) -> Result<Self, TimestampError> {
+        Self::from_bytes_16_bit_days(buf)
+    }
+}
+
+impl TimeReader for TimeProvider<DaysLen24Bits> {
+    fn from_bytes(buf: &[u8]) -> Result<Self, TimestampError> {
+        Self::from_bytes_24_bit_days(buf)
+    }
+}
+
+impl TimeWriter for TimeProvider<DaysLen16Bits> {
+    fn write_to_bytes(&self, buf: &mut [u8]) -> Result<usize, TimestampError> {
+        self.length_check(buf, self.len_as_bytes())?;
+        buf[0] = self.pfield;
+        buf[1..3].copy_from_slice(self.ccsds_days.to_be_bytes().as_slice());
+        buf[3..7].copy_from_slice(self.ms_of_day.to_be_bytes().as_slice());
+        if let Some(submillis_prec) = self.submillis_precision {
+            match submillis_prec {
+                SubmillisPrecision::Microseconds(ms) => {
+                    buf[7..9].copy_from_slice(ms.to_be_bytes().as_slice());
+                }
+                SubmillisPrecision::Picoseconds(ps) => {
+                    buf[7..11].copy_from_slice(ps.to_be_bytes().as_slice());
+                }
+                _ => (),
+            }
+        }
+        Ok(self.len_as_bytes())
+    }
+}
+
+impl TimeWriter for TimeProvider<DaysLen24Bits> {
+    fn write_to_bytes(&self, buf: &mut [u8]) -> Result<usize, TimestampError> {
+        self.length_check(buf, self.len_as_bytes())?;
+        buf[0] = self.pfield;
+        let be_days = self.ccsds_days.to_be_bytes();
+        buf[1..4].copy_from_slice(&be_days[1..4]);
+        buf[4..8].copy_from_slice(self.ms_of_day.to_be_bytes().as_slice());
+        if let Some(submillis_prec) = self.submillis_precision {
+            match submillis_prec {
+                SubmillisPrecision::Microseconds(ms) => {
+                    buf[8..10].copy_from_slice(ms.to_be_bytes().as_slice());
+                }
+                SubmillisPrecision::Picoseconds(ps) => {
+                    buf[8..12].copy_from_slice(ps.to_be_bytes().as_slice());
+                }
+                _ => (),
+            }
+        }
+        Ok(self.len_as_bytes())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::time::TimestampError::{ByteConversionError, InvalidTimeCode};
+    use crate::ByteConversionError::{FromSliceTooSmall, ToSliceTooSmall};
+    use chrono::{Datelike, Timelike};
+    #[cfg(feature = "serde")]
+    use postcard::{from_bytes, to_allocvec};
+    use std::format;
+
+    #[test]
+    fn test_time_stamp_zero_args() {
+        let time_stamper = TimeProvider::new_with_u16_days(0, 0);
+        assert_eq!(
+            time_stamper.unix_seconds(),
+            (DAYS_CCSDS_TO_UNIX * SECONDS_PER_DAY as i32) as i64
+        );
+        assert_eq!(time_stamper.submillis_precision(), None);
+        assert_eq!(time_stamper.ccdsd_time_code(), CcsdsTimeCodes::Cds);
+        assert_eq!(
+            time_stamper.p_field(),
+            (1, [(CcsdsTimeCodes::Cds as u8) << 4, 0])
+        );
+        let date_time = time_stamper.date_time().unwrap();
+        assert_eq!(date_time.year(), 1958);
+        assert_eq!(date_time.month(), 1);
+        assert_eq!(date_time.day(), 1);
+        assert_eq!(date_time.hour(), 0);
+        assert_eq!(date_time.minute(), 0);
+        assert_eq!(date_time.second(), 0);
+    }
+
+    #[test]
+    fn test_time_stamp_unix_epoch() {
+        let time_stamper = TimeProvider::new_with_u16_days((-DAYS_CCSDS_TO_UNIX) as u16, 0);
+        assert_eq!(time_stamper.unix_seconds(), 0);
+        assert_eq!(time_stamper.submillis_precision(), None);
+        let date_time = time_stamper.date_time().unwrap();
+        assert_eq!(date_time.year(), 1970);
+        assert_eq!(date_time.month(), 1);
+        assert_eq!(date_time.day(), 1);
+        assert_eq!(date_time.hour(), 0);
+        assert_eq!(date_time.minute(), 0);
+        assert_eq!(date_time.second(), 0);
+    }
+
+    #[test]
+    fn test_large_days_field_write() {
+        let time_stamper = TimeProvider::new_with_u24_days(0x108020, 0);
+        assert!(time_stamper.is_ok());
+        let time_stamper = time_stamper.unwrap();
+        assert_eq!(time_stamper.len_as_bytes(), 8);
+        let mut buf = [0; 16];
+        let written = time_stamper.write_to_bytes(&mut buf);
+        assert!(written.is_ok());
+        let written = written.unwrap();
+        assert_eq!(written, 8);
+        assert_eq!(buf[1], 0x10);
+        assert_eq!(buf[2], 0x80);
+        assert_eq!(buf[3], 0x20);
+        let ms = u32::from_be_bytes(buf[4..8].try_into().unwrap());
+        assert_eq!(ms, 0);
+        assert_eq!((buf[0] >> 2) & 0b1, 1);
+    }
+
+    #[test]
+    fn test_large_days_field_read() {
+        let time_stamper = TimeProvider::new_with_u24_days(0x108020, 0);
+        assert!(time_stamper.is_ok());
+        let time_stamper = time_stamper.unwrap();
+        let mut buf = [0; 16];
+        let written = time_stamper.write_to_bytes(&mut buf);
+        assert!(written.is_ok());
+        let provider = TimeProvider::<DaysLen24Bits>::from_bytes(&buf);
+        assert!(provider.is_ok());
+        let provider = provider.unwrap();
+        assert_eq!(provider.ccsds_days(), 0x108020);
+        assert_eq!(provider.ms_of_day(), 0);
+    }
+
+    #[test]
+    fn test_large_days_field_read_invalid_ctor() {
+        let time_stamper = TimeProvider::new_with_u24_days(0x108020, 0);
+        assert!(time_stamper.is_ok());
+        let time_stamper = time_stamper.unwrap();
+        let mut buf = [0; 16];
+        let written = time_stamper.write_to_bytes(&mut buf);
+        assert!(written.is_ok());
+        let faulty_ctor = TimeProvider::<DaysLen16Bits>::from_bytes(&buf);
+        assert!(faulty_ctor.is_err());
+        let error = faulty_ctor.unwrap_err();
+        if let TimestampError::CdsError(cds::CdsError::InvalidCtorForDaysOfLenInPreamble(
+            len_of_day,
+        )) = error
+        {
+            assert_eq!(len_of_day, LengthOfDaySegment::Long24Bits);
+        } else {
+            panic!("Wrong error type");
+        }
+    }
+
+    #[test]
+    fn test_write() {
+        let mut buf = [0; 16];
+        let time_stamper_0 = TimeProvider::new_with_u16_days(0, 0);
+        let mut res = time_stamper_0.write_to_bytes(&mut buf);
+        assert!(res.is_ok());
+        assert_eq!(buf[0], (CcsdsTimeCodes::Cds as u8) << 4);
+        assert_eq!(
+            u16::from_be_bytes(buf[1..3].try_into().expect("Byte conversion failed")),
+            0
+        );
+        assert_eq!(
+            u32::from_be_bytes(buf[3..7].try_into().expect("Byte conversion failed")),
+            0
+        );
+        let time_stamper_1 = TimeProvider::new_with_u16_days(u16::MAX - 1, u32::MAX - 1);
+        res = time_stamper_1.write_to_bytes(&mut buf);
+        assert!(res.is_ok());
+        assert_eq!(buf[0], (CcsdsTimeCodes::Cds as u8) << 4);
+        assert_eq!(
+            u16::from_be_bytes(buf[1..3].try_into().expect("Byte conversion failed")),
+            u16::MAX - 1
+        );
+        assert_eq!(
+            u32::from_be_bytes(buf[3..7].try_into().expect("Byte conversion failed")),
+            u32::MAX - 1
+        );
+    }
+
+    #[test]
+    fn test_faulty_write_buf_too_small() {
+        let mut buf = [0; 7];
+        let time_stamper = TimeProvider::new_with_u16_days(u16::MAX - 1, u32::MAX - 1);
+        for i in 0..6 {
+            let res = time_stamper.write_to_bytes(&mut buf[0..i]);
+            assert!(res.is_err());
+            match res.unwrap_err() {
+                ByteConversionError(ToSliceTooSmall(missmatch)) => {
+                    assert_eq!(missmatch.found, i);
+                    assert_eq!(missmatch.expected, 7);
+                }
+                _ => panic!(
+                    "{}",
+                    format!("Invalid error {:?} detected", res.unwrap_err())
+                ),
+            }
+        }
+    }
+
+    #[test]
+    fn test_faulty_read_buf_too_small() {
+        let buf = [0; 7];
+        for i in 0..6 {
+            let res = TimeProvider::<DaysLen16Bits>::from_bytes(&buf[0..i]);
+            assert!(res.is_err());
+            let err = res.unwrap_err();
+            match err {
+                ByteConversionError(e) => match e {
+                    FromSliceTooSmall(missmatch) => {
+                        assert_eq!(missmatch.found, i);
+                        assert_eq!(missmatch.expected, 7);
+                    }
+                    _ => panic!("{}", format!("Invalid error {:?} detected", e)),
+                },
+                _ => {
+                    panic!("Unexpected error {:?}", err);
+                }
+            }
+        }
+    }
+
+    #[test]
+    fn test_faulty_invalid_pfield() {
+        let mut buf = [0; 16];
+        let time_stamper_0 = TimeProvider::new_with_u16_days(0, 0);
+        let res = time_stamper_0.write_to_bytes(&mut buf);
+        assert!(res.is_ok());
+        buf[0] = 0;
+        let res = TimeProvider::<DaysLen16Bits>::from_bytes(&buf);
+        assert!(res.is_err());
+        let err = res.unwrap_err();
+        match err {
+            InvalidTimeCode(code, raw) => {
+                assert_eq!(code, CcsdsTimeCodes::Cds);
+                assert_eq!(raw, 0);
+            }
+            _ => {}
+        }
+    }
+
+    #[test]
+    fn test_reading() {
+        let mut buf = [0; 16];
+        let time_stamper = TimeProvider::new_with_u16_days(u16::MAX - 1, u32::MAX - 1);
+        let res = time_stamper.write_to_bytes(&mut buf);
+        assert!(res.is_ok());
+        assert_eq!(buf[0], (CcsdsTimeCodes::Cds as u8) << 4);
+        assert_eq!(
+            u16::from_be_bytes(buf[1..3].try_into().expect("Byte conversion failed")),
+            u16::MAX - 1
+        );
+        assert_eq!(
+            u32::from_be_bytes(buf[3..7].try_into().expect("Byte conversion failed")),
+            u32::MAX - 1
+        );
+
+        let read_stamp: TimeProvider<DaysLen16Bits> =
+            TimeProvider::from_bytes(&buf).expect("Reading timestamp failed");
+        assert_eq!(read_stamp.ccsds_days(), u16::MAX - 1);
+        assert_eq!(read_stamp.ms_of_day(), u32::MAX - 1);
+    }
+
+    #[test]
+    fn test_time_now() {
+        let timestamp_now = TimeProvider::from_now_with_u16_days().unwrap();
+        let compare_stamp = Utc::now();
+        let dt = timestamp_now.date_time().unwrap();
+        if compare_stamp.year() > dt.year() {
+            assert_eq!(compare_stamp.year() - dt.year(), 1);
+        } else {
+            assert_eq!(dt.year(), compare_stamp.year());
+        }
+        generic_dt_property_equality_check(dt.month(), compare_stamp.month(), 1, 12);
+
+        assert_eq!(dt.day(), compare_stamp.day());
+        if compare_stamp.day() < dt.day() {
+            assert!(dt.day() >= 28);
+            assert_eq!(compare_stamp.day(), 1);
+        } else if compare_stamp.day() > dt.day() {
+            assert_eq!(compare_stamp.day() - dt.day(), 1);
+        } else {
+            assert_eq!(compare_stamp.day(), dt.day());
+        }
+        generic_dt_property_equality_check(dt.hour(), compare_stamp.hour(), 0, 23);
+        generic_dt_property_equality_check(dt.minute(), compare_stamp.minute(), 0, 59);
+    }
+
+    #[test]
+    fn test_submillis_precision_micros() {
+        let mut time_stamper = TimeProvider::new_with_u16_days(0, 0);
+        time_stamper.set_submillis_precision(SubmillisPrecision::Microseconds(500));
+        assert!(time_stamper.submillis_precision().is_some());
+        if let SubmillisPrecision::Microseconds(micros) =
+            time_stamper.submillis_precision().unwrap()
+        {
+            assert_eq!(micros, 500);
+        } else {
+            panic!("Submillis precision was not set properly");
+        }
+        let mut write_buf: [u8; 16] = [0; 16];
+        let written = time_stamper
+            .write_to_bytes(&mut write_buf)
+            .expect("Writing timestamp failed");
+        assert_eq!(written, 9);
+        let cross_check: u16 = 500;
+        assert_eq!(write_buf[7..9], cross_check.to_be_bytes());
+    }
+
+    #[test]
+    fn test_submillis_precision_picos() {
+        let mut time_stamper = TimeProvider::new_with_u16_days(0, 0);
+        time_stamper.set_submillis_precision(SubmillisPrecision::Picoseconds(5e8 as u32));
+        assert!(time_stamper.submillis_precision().is_some());
+        if let SubmillisPrecision::Picoseconds(ps) = time_stamper.submillis_precision().unwrap() {
+            assert_eq!(ps, 5e8 as u32);
+        } else {
+            panic!("Submillis precision was not set properly");
+        }
+        let mut write_buf: [u8; 16] = [0; 16];
+        let written = time_stamper
+            .write_to_bytes(&mut write_buf)
+            .expect("Writing timestamp failed");
+        assert_eq!(written, 11);
+        let cross_check: u32 = 5e8 as u32;
+        assert_eq!(write_buf[7..11], cross_check.to_be_bytes());
+    }
+
+    #[test]
+    fn read_stamp_with_ps_submillis_precision() {
+        let mut time_stamper = TimeProvider::new_with_u16_days(0, 0);
+        time_stamper.set_submillis_precision(SubmillisPrecision::Picoseconds(5e8 as u32));
+        let mut write_buf: [u8; 16] = [0; 16];
+        let written = time_stamper
+            .write_to_bytes(&mut write_buf)
+            .expect("Writing timestamp failed");
+        assert_eq!(written, 11);
+        let stamp_deserialized = TimeProvider::<DaysLen16Bits>::from_bytes(&write_buf);
+        assert!(stamp_deserialized.is_ok());
+        let stamp_deserialized = stamp_deserialized.unwrap();
+        assert_eq!(stamp_deserialized.len_as_bytes(), 11);
+        assert!(stamp_deserialized.submillis_precision().is_some());
+        let submillis_rec = stamp_deserialized.submillis_precision().unwrap();
+        if let SubmillisPrecision::Picoseconds(ps) = submillis_rec {
+            assert_eq!(ps, 5e8 as u32);
+        } else {
+            panic!("Wrong precision field detected");
+        }
+    }
+
+    #[test]
+    fn read_stamp_with_us_submillis_precision() {
+        let mut time_stamper = TimeProvider::new_with_u16_days(0, 0);
+        time_stamper.set_submillis_precision(SubmillisPrecision::Microseconds(500));
+        let mut write_buf: [u8; 16] = [0; 16];
+        let written = time_stamper
+            .write_to_bytes(&mut write_buf)
+            .expect("Writing timestamp failed");
+        assert_eq!(written, 9);
+        let stamp_deserialized = TimeProvider::<DaysLen16Bits>::from_bytes(&write_buf);
+        assert!(stamp_deserialized.is_ok());
+        let stamp_deserialized = stamp_deserialized.unwrap();
+        assert_eq!(stamp_deserialized.len_as_bytes(), 9);
+        assert!(stamp_deserialized.submillis_precision().is_some());
+        let submillis_rec = stamp_deserialized.submillis_precision().unwrap();
+        if let SubmillisPrecision::Microseconds(us) = submillis_rec {
+            assert_eq!(us, 500);
+        } else {
+            panic!("Wrong precision field detected");
+        }
+    }
+
+    #[test]
+    #[cfg(feature = "serde")]
+    fn test_serialization() {
+        let stamp_now = TimeProvider::from_now_with_u16_days().expect("Error retrieving time");
+        let val = to_allocvec(&stamp_now).expect("Serializing timestamp failed");
+        assert!(val.len() > 0);
+        let stamp_deser: TimeProvider = from_bytes(&val).expect("Stamp deserialization failed");
+        assert_eq!(stamp_deser, stamp_now);
+    }
+
+    fn generic_dt_property_equality_check(first: u32, second: u32, start: u32, end: u32) {
+        if second < first {
+            assert_eq!(second, start);
+            assert_eq!(first, end);
+        } else if second > first {
+            assert_eq!(second - first, 1);
+        } else {
+            assert_eq!(first, second);
+        }
+    }
+}

src/time/cuc.rs

@@ -0,0 +1,950 @@
+//! Module to generate or read CCSDS Unsegmented (CUC) timestamps as specified in
+//! [CCSDS 301.0-B-4](https://public.ccsds.org/Pubs/301x0b4e1.pdf) section 3.2 .
+//!
+//! The core data structure to do this is the [TimeProviderCcsdsEpoch] struct.
+use super::*;
+use core::fmt::Debug;
+
+const MIN_CUC_LEN: usize = 2;
+
+/// Base value for the preamble field for a time field parser to determine the time field type.
+pub const P_FIELD_BASE: u8 = (CcsdsTimeCodes::CucCcsdsEpoch as u8) << 4;
+/// Maximum length if the preamble field is not extended.
+pub const MAX_CUC_LEN_SMALL_PREAMBLE: usize = 8;
+
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub enum FractionalResolution {
+    /// No fractional part, only second resolution
+    Seconds = 0,
+    /// 256 fractional parts, resulting in 1/255 ~= 4 ms fractional resolution
+    FourMs = 1,
+    /// 65535 fractional parts, resulting in 1/65535 ~= 15 us fractional resolution
+    FifteenUs = 2,
+    /// 16777215 fractional parts, resulting in 1/16777215 ~= 60 ns fractional resolution
+    SixtyNs = 3,
+}
+
+impl TryFrom<u8> for FractionalResolution {
+    type Error = ();
+
+    fn try_from(v: u8) -> Result<Self, Self::Error> {
+        match v {
+            0 => Ok(FractionalResolution::Seconds),
+            1 => Ok(FractionalResolution::FourMs),
+            2 => Ok(FractionalResolution::FifteenUs),
+            3 => Ok(FractionalResolution::SixtyNs),
+            _ => Err(()),
+        }
+    }
+}
+
+/// Please note that this function will panic if the fractional value is not smaller than
+/// the maximum number of fractions allowed for the particular resolution.
+/// (e.g. passing 270 when the resolution only allows 255 values).
+pub fn convert_fractional_part_to_ns(fractional_part: FractionalPart) -> u64 {
+    let div = fractional_res_to_div(fractional_part.0);
+    assert!(fractional_part.1 < div);
+    10_u64.pow(9) * fractional_part.1 as u64 / div as u64
+}
+
+pub const fn fractional_res_to_div(res: FractionalResolution) -> u32 {
+    2_u32.pow(8 * res as u32) - 1
+}
+
+/// Calculate the fractional part for a given resolution and subsecond nanoseconds.
+/// Please note that this function will panic if the passed nanoseconds exceeds 1 second
+/// as a nanosecond (10 to the power of 9). Furthermore, it will return [None] if the
+/// given resolution is [FractionalResolution::Seconds].
+pub fn fractional_part_from_subsec_ns(
+    res: FractionalResolution,
+    ns: u64,
+) -> Option<FractionalPart> {
+    if res == FractionalResolution::Seconds {
+        return None;
+    }
+    let sec_as_ns = 10_u64.pow(9);
+    if ns > sec_as_ns {
+        panic!("passed nanosecond value larger than 1 second");
+    }
+    let resolution = fractional_res_to_div(res) as u64;
+    // Use integer division because this can reduce code size of really small systems.
+    // First determine the nanoseconds for the smallest segment given the resolution.
+    // Then divide by that to find out the fractional part. For the calculation of the smallest
+    // fraction, we perform a ceiling division. This is because if we would use the default
+    // flooring division, we would divide by a smaller value, thereby allowing the calculation to
+    // invalid fractional parts which are too large. For the division of the nanoseconds by the
+    // smallest fraction, a flooring division is correct.
+    // The multiplication with 100000 is necessary to avoid precision loss during integer division.
+    // TODO: Floating point division might actually be faster option, but requires additional
+    //       code on small embedded systems..
+    let fractional_part = ns * 100000 / ((sec_as_ns * 100000 + resolution) / resolution);
+    // Floating point division.
+    //let fractional_part = (ns as f64 / ((sec_as_ns as f64) / resolution as f64)).floor() as u32;
+    Some(FractionalPart(res, fractional_part as u32))
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub enum CucError {
+    InvalidCounterWidth(u8),
+    InvalidFractionResolution(FractionalResolution),
+    InvalidCounter(u8, u64),
+    InvalidFractions(FractionalResolution, u64),
+}
+
+impl Display for CucError {
+    fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
+        match self {
+            CucError::InvalidCounterWidth(w) => {
+                write!(f, "invalid cuc counter byte width {}", w)
+            }
+            CucError::InvalidFractionResolution(w) => {
+                write!(f, "invalid cuc fractional part byte width {:?}", w)
+            }
+            CucError::InvalidCounter(w, c) => {
+                write!(f, "invalid cuc counter {} for width {}", c, w)
+            }
+            CucError::InvalidFractions(w, c) => {
+                write!(f, "invalid cuc fractional part {} for width {:?}", c, w)
+            }
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl Error for CucError {}
+
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub struct WidthCounterPair(u8, u32);
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub struct FractionalPart(FractionalResolution, u32);
+
+/// This object is the abstraction for the CCSDS Unsegmented Time Code (CUC) using the CCSDS epoch
+/// and a small preamble field.
+///
+/// It has the capability to generate and read timestamps as specified in the CCSDS 301.0-B-4
+/// section 3.2 . The preamble field only has one byte, which allows a time code representation
+/// through the year 2094. The time is represented as a simple binary counter starting from the
+/// fixed CCSDS epoch (1958-01-01 00:00:00). It is possible to provide subsecond accuracy using the
+/// fractional field with various available [resolutions][FractionalResolution].
+///
+/// Having a preamble field of one byte limits the width of the counter
+/// type (generally seconds) to 4 bytes and the width of the fractions type to 3 bytes. This limits
+/// the maximum time stamp size to [MAX_CUC_LEN_SMALL_PREAMBLE] (8 bytes).
+///
+/// # Example
+///
+/// ```
+/// use spacepackets::time::cuc::{FractionalResolution, TimeProviderCcsdsEpoch};
+/// use spacepackets::time::{TimeWriter, CcsdsTimeCodes, TimeReader, CcsdsTimeProvider};
+///
+/// // Highest fractional resolution
+/// let timestamp_now = TimeProviderCcsdsEpoch::from_now(FractionalResolution::SixtyNs).expect("creating cuc stamp failed");
+/// let mut raw_stamp = [0; 16];
+/// {
+///     let written = timestamp_now.write_to_bytes(&mut raw_stamp).expect("writing timestamp failed");
+///     assert_eq!((raw_stamp[0] >> 4) & 0b111, CcsdsTimeCodes::CucCcsdsEpoch as u8);
+///     // 1 byte preamble + 4 byte counter + 3 byte fractional part
+///     assert_eq!(written, 8);
+/// }
+/// {
+///     let read_result = TimeProviderCcsdsEpoch::from_bytes(&raw_stamp);
+///     assert!(read_result.is_ok());
+///     let stamp_deserialized = read_result.unwrap();
+///     assert_eq!(stamp_deserialized, timestamp_now);
+/// }
+/// ```
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub struct TimeProviderCcsdsEpoch {
+    pfield: u8,
+    counter: WidthCounterPair,
+    fractions: Option<FractionalPart>,
+}
+
+#[inline]
+pub fn pfield_len(pfield: u8) -> usize {
+    if ((pfield >> 7) & 0b1) == 1 {
+        return 2;
+    }
+    1
+}
+
+impl TimeProviderCcsdsEpoch {
+    /// Create a time provider with a four byte counter and no fractional part.
+    pub fn new(counter: u32) -> Self {
+        // These values are definitely valid, so it is okay to unwrap here.
+        Self::new_generic(WidthCounterPair(4, counter), None).unwrap()
+    }
+
+    /// Like [TimeProviderCcsdsEpoch::new] but allow to supply a fractional part as well.
+    pub fn new_with_fractions(counter: u32, fractions: FractionalPart) -> Result<Self, CucError> {
+        Self::new_generic(WidthCounterPair(4, counter), Some(fractions))
+    }
+
+    /// Fractions with a resolution of ~ 4 ms
+    pub fn new_with_coarse_fractions(counter: u32, subsec_fractions: u8) -> Self {
+        // These values are definitely valid, so it is okay to unwrap here.
+        Self::new_generic(
+            WidthCounterPair(4, counter),
+            Some(FractionalPart(
+                FractionalResolution::FourMs,
+                subsec_fractions as u32,
+            )),
+        )
+        .unwrap()
+    }
+
+    /// Fractions with a resolution of ~ 16 us
+    pub fn new_with_medium_fractions(counter: u32, subsec_fractions: u16) -> Self {
+        // These values are definitely valid, so it is okay to unwrap here.
+        Self::new_generic(
+            WidthCounterPair(4, counter),
+            Some(FractionalPart(
+                FractionalResolution::FifteenUs,
+                subsec_fractions as u32,
+            )),
+        )
+        .unwrap()
+    }
+
+    /// Fractions with a resolution of ~ 60 ns. The fractional part value is limited by the
+    /// 24 bits of the fractional field, so this function will fail with
+    /// [CucError::InvalidFractions] if the fractional value exceeds the value.
+    pub fn new_with_fine_fractions(counter: u32, subsec_fractions: u32) -> Result<Self, CucError> {
+        Self::new_generic(
+            WidthCounterPair(4, counter),
+            Some(FractionalPart(
+                FractionalResolution::SixtyNs,
+                subsec_fractions,
+            )),
+        )
+    }
+
+    /// This function will return the current time as a CUC timestamp.
+    /// The counter width will always be set to 4 bytes because the normal CCSDS epoch will overflow
+    /// when using less than that.
+    #[cfg(feature = "std")]
+    pub fn from_now(fraction_resolution: FractionalResolution) -> Result<Self, StdTimestampError> {
+        let now = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH)?;
+        let ccsds_epoch = unix_epoch_to_ccsds_epoch(now.as_secs());
+        if fraction_resolution == FractionalResolution::Seconds {
+            return Ok(Self::new(ccsds_epoch as u32));
+        }
+        let fractions =
+            fractional_part_from_subsec_ns(fraction_resolution, now.subsec_nanos() as u64);
+        Self::new_with_fractions(ccsds_epoch as u32, fractions.unwrap())
+            .map_err(|e| StdTimestampError::TimestampError(e.into()))
+    }
+
+    /// Updates the current time stamp from the current time. The fractional field width remains
+    /// the same and will be updated accordingly.
+    #[cfg(feature = "std")]
+    pub fn update_from_now(&mut self) -> Result<(), StdTimestampError> {
+        let now = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH)?;
+        self.counter.1 = unix_epoch_to_ccsds_epoch(now.as_secs()) as u32;
+        if self.fractions.is_some() {
+            self.fractions = fractional_part_from_subsec_ns(
+                self.fractions.unwrap().0,
+                now.subsec_nanos() as u64,
+            );
+        }
+        Ok(())
+    }
+
+    pub fn new_u16_counter(counter: u16) -> Self {
+        // These values are definitely valid, so it is okay to unwrap here.
+        Self::new_generic(WidthCounterPair(2, counter as u32), None).unwrap()
+    }
+
+    pub fn width_counter_pair(&self) -> WidthCounterPair {
+        self.counter
+    }
+
+    pub fn width_fractions_pair(&self) -> Option<FractionalPart> {
+        self.fractions
+    }
+
+    pub fn set_fractions(&mut self, fractions: FractionalPart) -> Result<(), CucError> {
+        Self::verify_fractions_width(fractions.0)?;
+        Self::verify_fractions_value(fractions)?;
+        self.fractions = Some(fractions);
+        self.update_p_field_fractions();
+        Ok(())
+    }
+
+    /// Set a fractional resolution. Please note that this function will reset the fractional value
+    /// to 0 if the resolution changes.
+    pub fn set_fractional_resolution(&mut self, res: FractionalResolution) {
+        if res == FractionalResolution::Seconds {
+            self.fractions = None;
+        }
+        let mut update_fractions = true;
+        if let Some(existing_fractions) = self.fractions {
+            if existing_fractions.0 == res {
+                update_fractions = false;
+            }
+        };
+        if update_fractions {
+            self.fractions = Some(FractionalPart(res, 0));
+        }
+    }
+
+    pub fn new_generic(
+        counter: WidthCounterPair,
+        fractions: Option<FractionalPart>,
+    ) -> Result<Self, CucError> {
+        Self::verify_counter_width(counter.0)?;
+        if counter.1 > (2u64.pow(counter.0 as u32 * 8) - 1) as u32 {
+            return Err(CucError::InvalidCounter(counter.0, counter.1 as u64));
+        }
+        if let Some(fractions) = fractions {
+            Self::verify_fractions_width(fractions.0)?;
+            Self::verify_fractions_value(fractions)?;
+        }
+        Ok(Self {
+            pfield: Self::build_p_field(counter.0, fractions.map(|v| v.0)),
+            counter,
+            fractions,
+        })
+    }
+
+    fn build_p_field(counter_width: u8, fractions_width: Option<FractionalResolution>) -> u8 {
+        let mut pfield = P_FIELD_BASE;
+        if !(1..=4).contains(&counter_width) {
+            // Okay to panic here, this function is private and all input values should
+            // have been sanitized
+            panic!("invalid counter width {} for cuc timestamp", counter_width);
+        }
+        pfield |= (counter_width - 1) << 2;
+        if let Some(fractions_width) = fractions_width {
+            if !(1..=3).contains(&(fractions_width as u8)) {
+                // Okay to panic here, this function is private and all input values should
+                // have been sanitized
+                panic!(
+                    "invalid fractions width {:?} for cuc timestamp",
+                    fractions_width
+                );
+            }
+            pfield |= fractions_width as u8;
+        }
+        pfield
+    }
+
+    fn update_p_field_fractions(&mut self) {
+        self.pfield &= !(0b11);
+        if let Some(fractions) = self.fractions {
+            self.pfield |= fractions.0 as u8;
+        }
+    }
+
+    #[inline]
+    pub fn len_cntr_from_pfield(pfield: u8) -> u8 {
+        ((pfield >> 2) & 0b11) + 1
+    }
+
+    #[inline]
+    pub fn len_fractions_from_pfield(pfield: u8) -> u8 {
+        pfield & 0b11
+    }
+
+    /// This returns the length of the individual components of the CUC timestamp in addition
+    /// to the total size.
+    ///
+    /// This function will return a tuple where the first value is the byte width of the
+    /// counter, the second value is the byte width of the fractional part, and the third
+    /// components is the total size.
+    pub fn len_components_and_total_from_pfield(pfield: u8) -> (u8, u8, usize) {
+        let base_len: usize = 1;
+        let cntr_len = Self::len_cntr_from_pfield(pfield);
+        let fractions_len = Self::len_fractions_from_pfield(pfield);
+        (
+            cntr_len,
+            fractions_len,
+            base_len + cntr_len as usize + fractions_len as usize,
+        )
+    }
+
+    pub fn len_packed_from_pfield(pfield: u8) -> usize {
+        let mut base_len: usize = 1;
+        base_len += Self::len_cntr_from_pfield(pfield) as usize;
+        base_len += Self::len_fractions_from_pfield(pfield) as usize;
+        base_len
+    }
+
+    /// Verifies the raw width parameter.
+    fn verify_counter_width(width: u8) -> Result<(), CucError> {
+        if width == 0 || width > 4 {
+            return Err(CucError::InvalidCounterWidth(width));
+        }
+        Ok(())
+    }
+
+    fn verify_fractions_width(width: FractionalResolution) -> Result<(), CucError> {
+        if width as u8 > 3 {
+            return Err(CucError::InvalidFractionResolution(width));
+        }
+        Ok(())
+    }
+
+    fn verify_fractions_value(val: FractionalPart) -> Result<(), CucError> {
+        if val.1 > 2u32.pow((val.0 as u32) * 8) - 1 {
+            return Err(CucError::InvalidFractions(val.0, val.1 as u64));
+        }
+        Ok(())
+    }
+}
+
+impl TimeReader for TimeProviderCcsdsEpoch {
+    fn from_bytes(buf: &[u8]) -> Result<Self, TimestampError>
+    where
+        Self: Sized,
+    {
+        if buf.len() < MIN_CUC_LEN {
+            return Err(TimestampError::ByteConversionError(
+                ByteConversionError::FromSliceTooSmall(SizeMissmatch {
+                    expected: MIN_CUC_LEN,
+                    found: buf.len(),
+                }),
+            ));
+        }
+        match ccsds_time_code_from_p_field(buf[0]) {
+            Ok(code) => {
+                if code != CcsdsTimeCodes::CucCcsdsEpoch {
+                    return Err(TimestampError::InvalidTimeCode(
+                        CcsdsTimeCodes::CucCcsdsEpoch,
+                        code as u8,
+                    ));
+                }
+            }
+            Err(raw) => {
+                return Err(TimestampError::InvalidTimeCode(
+                    CcsdsTimeCodes::CucCcsdsEpoch,
+                    raw,
+                ))
+            }
+        }
+        let (cntr_len, fractions_len, total_len) =
+            Self::len_components_and_total_from_pfield(buf[0]);
+        if buf.len() < total_len {
+            return Err(TimestampError::ByteConversionError(
+                ByteConversionError::FromSliceTooSmall(SizeMissmatch {
+                    expected: total_len,
+                    found: buf.len(),
+                }),
+            ));
+        }
+        let mut current_idx = 1;
+        let counter = match cntr_len {
+            1 => buf[current_idx] as u32,
+            2 => u16::from_be_bytes(buf[current_idx..current_idx + 2].try_into().unwrap()) as u32,
+            3 => {
+                let mut tmp_buf: [u8; 4] = [0; 4];
+                tmp_buf[1..4].copy_from_slice(&buf[current_idx..current_idx + 3]);
+                u32::from_be_bytes(tmp_buf)
+            }
+            4 => u32::from_be_bytes(buf[current_idx..current_idx + 4].try_into().unwrap()),
+            _ => panic!("unreachable match arm"),
+        };
+        current_idx += cntr_len as usize;
+        let mut fractions = None;
+        if fractions_len > 0 {
+            match fractions_len {
+                1 => {
+                    fractions = Some(FractionalPart(
+                        fractions_len.try_into().unwrap(),
+                        buf[current_idx] as u32,
+                    ))
+                }
+                2 => {
+                    fractions = Some(FractionalPart(
+                        fractions_len.try_into().unwrap(),
+                        u16::from_be_bytes(buf[current_idx..current_idx + 2].try_into().unwrap())
+                            as u32,
+                    ))
+                }
+                3 => {
+                    let mut tmp_buf: [u8; 4] = [0; 4];
+                    tmp_buf[1..4].copy_from_slice(&buf[current_idx..current_idx + 3]);
+                    fractions = Some(FractionalPart(
+                        fractions_len.try_into().unwrap(),
+                        u32::from_be_bytes(tmp_buf),
+                    ))
+                }
+                _ => panic!("unreachable match arm"),
+            }
+        }
+        let provider = Self::new_generic(WidthCounterPair(cntr_len, counter), fractions)?;
+        Ok(provider)
+    }
+}
+
+impl TimeWriter for TimeProviderCcsdsEpoch {
+    fn write_to_bytes(&self, bytes: &mut [u8]) -> Result<usize, TimestampError> {
+        // Cross check the sizes of the counters against byte widths in the ctor
+        if bytes.len() < self.len_as_bytes() {
+            return Err(TimestampError::ByteConversionError(
+                ByteConversionError::ToSliceTooSmall(SizeMissmatch {
+                    found: bytes.len(),
+                    expected: self.len_as_bytes(),
+                }),
+            ));
+        }
+        bytes[0] = self.pfield;
+        let mut current_idx: usize = 1;
+        match self.counter.0 {
+            1 => {
+                bytes[current_idx] = self.counter.1 as u8;
+            }
+            2 => {
+                bytes[current_idx..current_idx + 2]
+                    .copy_from_slice(&(self.counter.1 as u16).to_be_bytes());
+            }
+            3 => {
+                bytes[current_idx..current_idx + 3]
+                    .copy_from_slice(&self.counter.1.to_be_bytes()[1..4]);
+            }
+            4 => {
+                bytes[current_idx..current_idx + 4].copy_from_slice(&self.counter.1.to_be_bytes());
+            }
+            // Should never happen
+            _ => panic!("invalid counter width value"),
+        }
+        current_idx += self.counter.0 as usize;
+        if let Some(fractions) = self.fractions {
+            match fractions.0 {
+                FractionalResolution::FourMs => bytes[current_idx] = fractions.1 as u8,
+                FractionalResolution::FifteenUs => bytes[current_idx..current_idx + 2]
+                    .copy_from_slice(&(fractions.1 as u16).to_be_bytes()),
+                FractionalResolution::SixtyNs => bytes[current_idx..current_idx + 3]
+                    .copy_from_slice(&fractions.1.to_be_bytes()[1..4]),
+                // Should also never happen
+                _ => panic!("invalid fractions value"),
+            }
+            current_idx += fractions.0 as usize;
+        }
+        Ok(current_idx)
+    }
+}
+
+impl CcsdsTimeProvider for TimeProviderCcsdsEpoch {
+    fn len_as_bytes(&self) -> usize {
+        Self::len_packed_from_pfield(self.pfield)
+    }
+
+    fn p_field(&self) -> (usize, [u8; 2]) {
+        (1, [self.pfield, 0])
+    }
+
+    fn ccdsd_time_code(&self) -> CcsdsTimeCodes {
+        CcsdsTimeCodes::CucCcsdsEpoch
+    }
+
+    /// Please note that this function only works as intended if the time counter resolution
+    /// is one second.
+    fn unix_seconds(&self) -> i64 {
+        ccsds_epoch_to_unix_epoch(self.counter.1 as u64) as i64
+    }
+
+    fn date_time(&self) -> Option<DateTime<Utc>> {
+        let unix_seconds = self.unix_seconds();
+        let ns = if let Some(fractional_part) = self.fractions {
+            convert_fractional_part_to_ns(fractional_part)
+        } else {
+            0
+        };
+        if let LocalResult::Single(res) = Utc.timestamp_opt(unix_seconds, ns as u32) {
+            return Some(res);
+        }
+        None
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use chrono::{Datelike, Timelike};
+    #[allow(unused_imports)]
+    use std::println;
+
+    #[test]
+    fn test_basic_zero_epoch() {
+        let zero_cuc = TimeProviderCcsdsEpoch::new(0);
+        assert_eq!(zero_cuc.len_as_bytes(), 5);
+        assert_eq!(zero_cuc.ccdsd_time_code(), CcsdsTimeCodes::CucCcsdsEpoch);
+        let counter = zero_cuc.width_counter_pair();
+        assert_eq!(counter.0, 4);
+        assert_eq!(counter.1, 0);
+        let fractions = zero_cuc.width_fractions_pair();
+        assert!(fractions.is_none());
+        let dt = zero_cuc.date_time();
+        assert!(dt.is_some());
+        let dt = dt.unwrap();
+        assert_eq!(dt.year(), 1958);
+        assert_eq!(dt.month(), 1);
+        assert_eq!(dt.day(), 1);
+        assert_eq!(dt.hour(), 0);
+        assert_eq!(dt.minute(), 0);
+        assert_eq!(dt.second(), 0);
+    }
+
+    #[test]
+    fn test_write_no_fractions() {
+        let mut buf: [u8; 16] = [0; 16];
+        let zero_cuc = TimeProviderCcsdsEpoch::new_generic(WidthCounterPair(4, 0x20102030), None);
+        assert!(zero_cuc.is_ok());
+        let zero_cuc = zero_cuc.unwrap();
+        let res = zero_cuc.write_to_bytes(&mut buf);
+        assert!(res.is_ok());
+        assert_eq!(zero_cuc.len_as_bytes(), 5);
+        assert_eq!(pfield_len(buf[0]), 1);
+        let written = res.unwrap();
+        assert_eq!(written, 5);
+        assert_eq!((buf[0] >> 7) & 0b1, 0);
+        let time_code = ccsds_time_code_from_p_field(buf[0]);
+        assert!(time_code.is_ok());
+        assert_eq!(time_code.unwrap(), CcsdsTimeCodes::CucCcsdsEpoch);
+        assert_eq!((buf[0] >> 2) & 0b11, 0b11);
+        assert_eq!(buf[0] & 0b11, 0);
+        let raw_counter = u32::from_be_bytes(buf[1..5].try_into().unwrap());
+        assert_eq!(raw_counter, 0x20102030);
+        assert_eq!(buf[5], 0);
+    }
+
+    #[test]
+    fn test_datetime_now() {
+        let now = Utc::now();
+        let cuc_now = TimeProviderCcsdsEpoch::from_now(FractionalResolution::SixtyNs);
+        assert!(cuc_now.is_ok());
+        let cuc_now = cuc_now.unwrap();
+        let dt_opt = cuc_now.date_time();
+        assert!(dt_opt.is_some());
+        let dt = dt_opt.unwrap();
+        let diff = dt - now;
+        assert!(diff.num_milliseconds() < 1000);
+        println!("datetime from cuc: {}", dt);
+        println!("datetime now: {}", now);
+    }
+
+    #[test]
+    fn test_read_no_fractions() {
+        let mut buf: [u8; 16] = [0; 16];
+        let zero_cuc =
+            TimeProviderCcsdsEpoch::new_generic(WidthCounterPair(4, 0x20102030), None).unwrap();
+        zero_cuc.write_to_bytes(&mut buf).unwrap();
+        let cuc_read_back =
+            TimeProviderCcsdsEpoch::from_bytes(&buf).expect("reading cuc timestamp failed");
+        assert_eq!(cuc_read_back, zero_cuc);
+        assert_eq!(cuc_read_back.width_counter_pair().1, 0x20102030);
+        assert_eq!(cuc_read_back.width_fractions_pair(), None);
+    }
+
+    #[test]
+    fn invalid_read_len() {
+        let mut buf: [u8; 16] = [0; 16];
+        for i in 0..2 {
+            let res = TimeProviderCcsdsEpoch::from_bytes(&buf[0..i]);
+            assert!(res.is_err());
+            let err = res.unwrap_err();
+            if let TimestampError::ByteConversionError(ByteConversionError::FromSliceTooSmall(e)) =
+                err
+            {
+                assert_eq!(e.found, i);
+                assert_eq!(e.expected, 2);
+            }
+        }
+        let large_stamp = TimeProviderCcsdsEpoch::new_with_fine_fractions(22, 300).unwrap();
+        large_stamp.write_to_bytes(&mut buf).unwrap();
+        for i in 2..large_stamp.len_as_bytes() - 1 {
+            let res = TimeProviderCcsdsEpoch::from_bytes(&buf[0..i]);
+            assert!(res.is_err());
+            let err = res.unwrap_err();
+            if let TimestampError::ByteConversionError(ByteConversionError::FromSliceTooSmall(e)) =
+                err
+            {
+                assert_eq!(e.found, i);
+                assert_eq!(e.expected, large_stamp.len_as_bytes());
+            }
+        }
+    }
+
+    #[test]
+    fn write_and_read_tiny_stamp() {
+        let mut buf = [0; 2];
+        let cuc = TimeProviderCcsdsEpoch::new_generic(WidthCounterPair(1, 200), None);
+        assert!(cuc.is_ok());
+        let cuc = cuc.unwrap();
+        assert_eq!(cuc.len_as_bytes(), 2);
+        let res = cuc.write_to_bytes(&mut buf);
+        assert!(res.is_ok());
+        let written = res.unwrap();
+        assert_eq!(written, 2);
+        assert_eq!(buf[1], 200);
+        let cuc_read_back = TimeProviderCcsdsEpoch::from_bytes(&buf);
+        assert!(cuc_read_back.is_ok());
+        let cuc_read_back = cuc_read_back.unwrap();
+        assert_eq!(cuc_read_back, cuc);
+    }
+
+    #[test]
+    fn write_slightly_larger_stamp() {
+        let mut buf = [0; 4];
+        let cuc = TimeProviderCcsdsEpoch::new_generic(WidthCounterPair(2, 40000), None);
+        assert!(cuc.is_ok());
+        let cuc = cuc.unwrap();
+        assert_eq!(cuc.len_as_bytes(), 3);
+        let res = cuc.write_to_bytes(&mut buf);
+        assert!(res.is_ok());
+        let written = res.unwrap();
+        assert_eq!(written, 3);
+        assert_eq!(u16::from_be_bytes(buf[1..3].try_into().unwrap()), 40000);
+        let cuc_read_back = TimeProviderCcsdsEpoch::from_bytes(&buf);
+        assert!(cuc_read_back.is_ok());
+        let cuc_read_back = cuc_read_back.unwrap();
+        assert_eq!(cuc_read_back, cuc);
+    }
+
+    #[test]
+    fn invalid_buf_len_for_read() {}
+    #[test]
+    fn write_read_three_byte_cntr_stamp() {
+        let mut buf = [0; 4];
+        let cuc = TimeProviderCcsdsEpoch::new_generic(WidthCounterPair(3, 2_u32.pow(24) - 2), None);
+        assert!(cuc.is_ok());
+        let cuc = cuc.unwrap();
+        assert_eq!(cuc.len_as_bytes(), 4);
+        let res = cuc.write_to_bytes(&mut buf);
+        assert!(res.is_ok());
+        let written = res.unwrap();
+        assert_eq!(written, 4);
+        let mut temp_buf = [0; 4];
+        temp_buf[1..4].copy_from_slice(&buf[1..4]);
+        assert_eq!(u32::from_be_bytes(temp_buf), 2_u32.pow(24) - 2);
+        let cuc_read_back = TimeProviderCcsdsEpoch::from_bytes(&buf);
+        assert!(cuc_read_back.is_ok());
+        let cuc_read_back = cuc_read_back.unwrap();
+        assert_eq!(cuc_read_back, cuc);
+    }
+
+    #[test]
+    fn test_write_invalid_buf() {
+        let mut buf: [u8; 16] = [0; 16];
+        let res = TimeProviderCcsdsEpoch::new_with_fine_fractions(0, 0);
+        let cuc = res.unwrap();
+        for i in 0..cuc.len_as_bytes() - 1 {
+            let err = cuc.write_to_bytes(&mut buf[0..i]);
+            assert!(err.is_err());
+            let err = err.unwrap_err();
+            if let TimestampError::ByteConversionError(ByteConversionError::ToSliceTooSmall(e)) =
+                err
+            {
+                assert_eq!(e.expected, cuc.len_as_bytes());
+                assert_eq!(e.found, i);
+            } else {
+                panic!("unexpected error: {}", err);
+            }
+        }
+    }
+    #[test]
+    fn invalid_ccsds_stamp_type() {
+        let mut buf: [u8; 16] = [0; 16];
+        buf[0] |= (CcsdsTimeCodes::CucAgencyEpoch as u8) << 4;
+        let res = TimeProviderCcsdsEpoch::from_bytes(&buf);
+        assert!(res.is_err());
+        let err = res.unwrap_err();
+        if let TimestampError::InvalidTimeCode(code, raw) = err {
+            assert_eq!(code, CcsdsTimeCodes::CucCcsdsEpoch);
+            assert_eq!(raw, CcsdsTimeCodes::CucAgencyEpoch as u8);
+        } else {
+            panic!("unexpected error: {}", err);
+        }
+    }
+
+    #[test]
+    fn test_write_with_coarse_fractions() {
+        let mut buf: [u8; 16] = [0; 16];
+        let cuc = TimeProviderCcsdsEpoch::new_with_coarse_fractions(0x30201060, 120);
+        assert!(cuc.fractions.is_some());
+        assert_eq!(cuc.fractions.unwrap().1, 120);
+        assert_eq!(cuc.fractions.unwrap().0, FractionalResolution::FourMs);
+        let res = cuc.write_to_bytes(&mut buf);
+        assert!(res.is_ok());
+        let written = res.unwrap();
+        assert_eq!(written, 6);
+        assert_eq!(buf[5], 120);
+        assert_eq!(buf[6], 0);
+        assert_eq!(
+            u32::from_be_bytes(buf[1..5].try_into().unwrap()),
+            0x30201060
+        );
+    }
+
+    #[test]
+    fn test_read_with_coarse_fractions() {
+        let mut buf: [u8; 16] = [0; 16];
+        let cuc = TimeProviderCcsdsEpoch::new_with_coarse_fractions(0x30201060, 120);
+        let res = cuc.write_to_bytes(&mut buf);
+        assert!(res.is_ok());
+        let res = TimeProviderCcsdsEpoch::from_bytes(&buf);
+        assert!(res.is_ok());
+        let read_back = res.unwrap();
+        assert_eq!(read_back, cuc);
+    }
+
+    #[test]
+    fn test_write_with_medium_fractions() {
+        let mut buf: [u8; 16] = [0; 16];
+        let cuc = TimeProviderCcsdsEpoch::new_with_medium_fractions(0x30303030, 30000);
+        let res = cuc.write_to_bytes(&mut buf);
+        assert!(res.is_ok());
+        let written = res.unwrap();
+        assert_eq!(written, 7);
+        assert_eq!(u16::from_be_bytes(buf[5..7].try_into().unwrap()), 30000);
+        assert_eq!(buf[7], 0);
+    }
+
+    #[test]
+    fn test_read_with_medium_fractions() {
+        let mut buf: [u8; 16] = [0; 16];
+        let cuc = TimeProviderCcsdsEpoch::new_with_medium_fractions(0x30303030, 30000);
+        let res = cuc.write_to_bytes(&mut buf);
+        assert!(res.is_ok());
+        let res = TimeProviderCcsdsEpoch::from_bytes(&buf);
+        assert!(res.is_ok());
+        let cuc_read_back = res.unwrap();
+        assert_eq!(cuc_read_back, cuc);
+    }
+
+    #[test]
+    fn test_write_with_fine_fractions() {
+        let mut buf: [u8; 16] = [0; 16];
+        let cuc =
+            TimeProviderCcsdsEpoch::new_with_fine_fractions(0x30303030, u16::MAX as u32 + 60000);
+        assert!(cuc.is_ok());
+        let cuc = cuc.unwrap();
+        let res = cuc.write_to_bytes(&mut buf);
+        let written = res.unwrap();
+        assert_eq!(written, 8);
+        let mut dummy_buf: [u8; 4] = [0; 4];
+        dummy_buf[1..4].copy_from_slice(&buf[5..8]);
+        assert_eq!(u32::from_be_bytes(dummy_buf), u16::MAX as u32 + 60000);
+        assert_eq!(buf[8], 0);
+    }
+
+    #[test]
+    fn test_read_with_fine_fractions() {
+        let mut buf: [u8; 16] = [0; 16];
+        let cuc =
+            TimeProviderCcsdsEpoch::new_with_fine_fractions(0x30303030, u16::MAX as u32 + 60000);
+        assert!(cuc.is_ok());
+        let cuc = cuc.unwrap();
+        let res = cuc.write_to_bytes(&mut buf);
+        assert!(res.is_ok());
+        let res = TimeProviderCcsdsEpoch::from_bytes(&buf);
+        assert!(res.is_ok());
+        let cuc_read_back = res.unwrap();
+        assert_eq!(cuc_read_back, cuc);
+    }
+
+    #[test]
+    fn test_fractional_converter() {
+        let ns = convert_fractional_part_to_ns(FractionalPart(FractionalResolution::FourMs, 2));
+        // The formula for this is 2/255 * 10e9 = 7.843.137.
+        assert_eq!(ns, 7843137);
+        // This is the largest value we should be able to pass without this function panicking.
+        let ns = convert_fractional_part_to_ns(FractionalPart(
+            FractionalResolution::SixtyNs,
+            2_u32.pow(24) - 2,
+        ));
+        assert_eq!(ns, 999999940);
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_fractional_converter_invalid_input() {
+        convert_fractional_part_to_ns(FractionalPart(FractionalResolution::FourMs, 256));
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_fractional_converter_invalid_input_2() {
+        convert_fractional_part_to_ns(FractionalPart(
+            FractionalResolution::SixtyNs,
+            2_u32.pow(32) - 1,
+        ));
+    }
+
+    #[test]
+    fn fractional_part_formula() {
+        let fractional_part =
+            fractional_part_from_subsec_ns(FractionalResolution::FourMs, 7843138).unwrap();
+        assert_eq!(fractional_part.1, 2);
+    }
+
+    #[test]
+    fn fractional_part_formula_2() {
+        let fractional_part =
+            fractional_part_from_subsec_ns(FractionalResolution::FourMs, 12000000).unwrap();
+        assert_eq!(fractional_part.1, 3);
+    }
+
+    #[test]
+    fn fractional_part_formula_3() {
+        let one_fraction_with_width_two_in_ns =
+            10_u64.pow(9) as f64 / (2_u32.pow(8 * 2) - 1) as f64;
+        assert_eq!(one_fraction_with_width_two_in_ns.ceil(), 15260.0);
+        let hundred_fractions_and_some =
+            (100.0 * one_fraction_with_width_two_in_ns).floor() as u64 + 7000;
+        let fractional_part = fractional_part_from_subsec_ns(
+            FractionalResolution::FifteenUs,
+            hundred_fractions_and_some,
+        )
+        .unwrap();
+        assert_eq!(fractional_part.1, 100);
+        // Using exactly 101.0 can yield values which will later be rounded down to 100
+        let hundred_and_one_fractions =
+            (101.001 * one_fraction_with_width_two_in_ns).floor() as u64;
+        let fractional_part = fractional_part_from_subsec_ns(
+            FractionalResolution::FifteenUs,
+            hundred_and_one_fractions,
+        )
+        .unwrap();
+        assert_eq!(fractional_part.1, 101);
+    }
+
+    #[test]
+    fn update_fractions() {
+        let mut stamp = TimeProviderCcsdsEpoch::new(2000);
+        let res = stamp.set_fractions(FractionalPart(FractionalResolution::SixtyNs, 5000));
+        assert!(res.is_ok());
+        assert!(stamp.fractions.is_some());
+        let fractions = stamp.fractions.unwrap();
+        assert_eq!(fractions.0, FractionalResolution::SixtyNs);
+        assert_eq!(fractions.1, 5000);
+    }
+
+    #[test]
+    fn set_fract_resolution() {
+        let mut stamp = TimeProviderCcsdsEpoch::new(2000);
+        stamp.set_fractional_resolution(FractionalResolution::SixtyNs);
+        assert!(stamp.fractions.is_some());
+        let fractions = stamp.fractions.unwrap();
+        assert_eq!(fractions.0, FractionalResolution::SixtyNs);
+        assert_eq!(fractions.1, 0);
+        let res = stamp.update_from_now();
+        assert!(res.is_ok());
+    }
+
+    #[test]
+    fn assert_largest_fractions() {
+        let fractions =
+            fractional_part_from_subsec_ns(FractionalResolution::SixtyNs, 10u64.pow(9) - 1)
+                .unwrap();
+        // The value can not be larger than representable by 3 bytes
+        // Assert that the maximum resolution can be reached
+        assert_eq!(fractions.1, 2_u32.pow(3 * 8) - 2);
+    }
+}

src/time/mod.rs

@@ -0,0 +1,243 @@
+//! CCSDS Time Code Formats according to [CCSDS 301.0-B-4](https://public.ccsds.org/Pubs/301x0b4e1.pdf)
+use crate::{ByteConversionError, SizeMissmatch};
+use chrono::{DateTime, LocalResult, TimeZone, Utc};
+use core::fmt::{Display, Formatter};
+
+#[allow(unused_imports)]
+#[cfg(not(feature = "std"))]
+use num_traits::float::FloatCore;
+
+#[cfg(feature = "serde")]
+use serde::{Deserialize, Serialize};
+#[cfg(feature = "std")]
+use std::error::Error;
+#[cfg(feature = "std")]
+use std::time::{SystemTime, SystemTimeError};
+
+pub mod ascii;
+pub mod cds;
+pub mod cuc;
+
+pub const DAYS_CCSDS_TO_UNIX: i32 = -4383;
+pub const SECONDS_PER_DAY: u32 = 86400;
+
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub enum CcsdsTimeCodes {
+    CucCcsdsEpoch = 0b001,
+    CucAgencyEpoch = 0b010,
+    Cds = 0b100,
+    Ccs = 0b101,
+    AgencyDefined = 0b110,
+}
+
+impl TryFrom<u8> for CcsdsTimeCodes {
+    type Error = ();
+
+    fn try_from(value: u8) -> Result<Self, Self::Error> {
+        match value {
+            x if x == CcsdsTimeCodes::CucCcsdsEpoch as u8 => Ok(CcsdsTimeCodes::CucCcsdsEpoch),
+            x if x == CcsdsTimeCodes::CucAgencyEpoch as u8 => Ok(CcsdsTimeCodes::CucAgencyEpoch),
+            x if x == CcsdsTimeCodes::Cds as u8 => Ok(CcsdsTimeCodes::Cds),
+            x if x == CcsdsTimeCodes::Ccs as u8 => Ok(CcsdsTimeCodes::Ccs),
+            x if x == CcsdsTimeCodes::AgencyDefined as u8 => Ok(CcsdsTimeCodes::AgencyDefined),
+            _ => Err(()),
+        }
+    }
+}
+
+/// Retrieve the CCSDS time code from the p-field. If no valid time code identifier is found, the
+/// value of the raw time code identification field is returned.
+pub fn ccsds_time_code_from_p_field(pfield: u8) -> Result<CcsdsTimeCodes, u8> {
+    let raw_bits = (pfield >> 4) & 0b111;
+    CcsdsTimeCodes::try_from(raw_bits).map_err(|_| raw_bits)
+}
+
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub enum TimestampError {
+    /// Contains tuple where first value is the expected time code and the second
+    /// value is the found raw value
+    InvalidTimeCode(CcsdsTimeCodes, u8),
+    ByteConversionError(ByteConversionError),
+    CdsError(cds::CdsError),
+    CucError(cuc::CucError),
+    CustomEpochNotSupported,
+}
+
+impl From<cds::CdsError> for TimestampError {
+    fn from(e: cds::CdsError) -> Self {
+        TimestampError::CdsError(e)
+    }
+}
+
+impl From<cuc::CucError> for TimestampError {
+    fn from(e: cuc::CucError) -> Self {
+        TimestampError::CucError(e)
+    }
+}
+
+#[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+#[derive(Debug, Clone)]
+pub enum StdTimestampError {
+    SystemTimeError(SystemTimeError),
+    TimestampError(TimestampError),
+}
+
+#[cfg(feature = "std")]
+impl From<TimestampError> for StdTimestampError {
+    fn from(v: TimestampError) -> Self {
+        Self::TimestampError(v)
+    }
+}
+
+#[cfg(feature = "std")]
+impl From<SystemTimeError> for StdTimestampError {
+    fn from(v: SystemTimeError) -> Self {
+        Self::SystemTimeError(v)
+    }
+}
+
+impl Display for TimestampError {
+    fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
+        match self {
+            TimestampError::InvalidTimeCode(time_code, raw_val) => {
+                write!(
+                    f,
+                    "invalid raw time code value {} for time code {:?}",
+                    raw_val, time_code
+                )
+            }
+            TimestampError::CdsError(e) => {
+                write!(f, "cds error {}", e)
+            }
+            TimestampError::CucError(e) => {
+                write!(f, "cuc error {}", e)
+            }
+            TimestampError::ByteConversionError(e) => {
+                write!(f, "byte conversion error {}", e)
+            }
+            TimestampError::CustomEpochNotSupported => {
+                write!(f, "custom epochs are not supported")
+            }
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl Error for TimestampError {
+    fn source(&self) -> Option<&(dyn Error + 'static)> {
+        match self {
+            TimestampError::ByteConversionError(e) => Some(e),
+            TimestampError::CdsError(e) => Some(e),
+            TimestampError::CucError(e) => Some(e),
+            _ => None,
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+pub fn seconds_since_epoch() -> f64 {
+    SystemTime::now()
+        .duration_since(SystemTime::UNIX_EPOCH)
+        .expect("System time generation failed")
+        .as_secs_f64()
+}
+
+/// Convert UNIX days to CCSDS days
+///
+///  - CCSDS epoch: 1958 January 1
+///  - UNIX Epoch: 1970 January 1
+pub const fn unix_to_ccsds_days(unix_days: i64) -> i64 {
+    unix_days - DAYS_CCSDS_TO_UNIX as i64
+}
+
+/// Convert CCSDS days to UNIX days
+///
+///  - CCSDS epoch: 1958 January 1
+///  - UNIX Epoch: 1970 January 1
+pub const fn ccsds_to_unix_days(ccsds_days: i64) -> i64 {
+    ccsds_days + DAYS_CCSDS_TO_UNIX as i64
+}
+
+/// Similar to [unix_to_ccsds_days] but converts the epoch instead, which is the number of elpased
+/// seconds since the CCSDS and UNIX epoch times.
+pub const fn unix_epoch_to_ccsds_epoch(unix_epoch: u64) -> u64 {
+    (unix_epoch as i64 - (DAYS_CCSDS_TO_UNIX as i64 * SECONDS_PER_DAY as i64)) as u64
+}
+
+pub const fn ccsds_epoch_to_unix_epoch(ccsds_epoch: u64) -> u64 {
+    (ccsds_epoch as i64 + (DAYS_CCSDS_TO_UNIX as i64 * SECONDS_PER_DAY as i64)) as u64
+}
+
+#[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+pub fn ms_of_day_using_sysclock() -> u32 {
+    ms_of_day(seconds_since_epoch())
+}
+
+pub fn ms_of_day(seconds_since_epoch: f64) -> u32 {
+    let fraction_ms = seconds_since_epoch - seconds_since_epoch.floor();
+    let ms_of_day: u32 = (((seconds_since_epoch.floor() as u32 % SECONDS_PER_DAY) * 1000) as f64
+        + fraction_ms)
+        .floor() as u32;
+    ms_of_day
+}
+
+pub trait TimeWriter {
+    /// Generic function to convert write a timestamp into a raw buffer.
+    /// Returns the number of written bytes on success.
+    fn write_to_bytes(&self, bytes: &mut [u8]) -> Result<usize, TimestampError>;
+}
+
+pub trait TimeReader {
+    fn from_bytes(buf: &[u8]) -> Result<Self, TimestampError>
+    where
+        Self: Sized;
+}
+
+/// Trait for generic CCSDS time providers.
+pub trait CcsdsTimeProvider {
+    fn len_as_bytes(&self) -> usize;
+
+    /// Returns the pfield of the time provider. The pfield can have one or two bytes depending
+    /// on the extension bit (first bit). The time provider should returns a tuple where the first
+    /// entry denotes the length of the pfield and the second entry is the value of the pfield
+    /// in big endian format.
+    fn p_field(&self) -> (usize, [u8; 2]);
+    fn ccdsd_time_code(&self) -> CcsdsTimeCodes;
+    fn unix_seconds(&self) -> i64;
+    fn date_time(&self) -> Option<DateTime<Utc>>;
+}
+
+#[cfg(all(test, feature = "std"))]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_days_conversion() {
+        assert_eq!(unix_to_ccsds_days(DAYS_CCSDS_TO_UNIX.into()), 0);
+        assert_eq!(ccsds_to_unix_days(0), DAYS_CCSDS_TO_UNIX.into());
+    }
+
+    #[test]
+    fn test_get_current_time() {
+        let sec_floats = seconds_since_epoch();
+        assert!(sec_floats > 0.0);
+    }
+
+    #[test]
+    fn test_ccsds_epoch() {
+        let now = SystemTime::now()
+            .duration_since(SystemTime::UNIX_EPOCH)
+            .unwrap();
+        let unix_epoch = now.as_secs();
+        let ccsds_epoch = unix_epoch_to_ccsds_epoch(now.as_secs());
+        assert!(ccsds_epoch > unix_epoch);
+        assert_eq!((ccsds_epoch - unix_epoch) % SECONDS_PER_DAY as u64, 0);
+        let days_diff = (ccsds_epoch - unix_epoch) / SECONDS_PER_DAY as u64;
+        assert_eq!(days_diff, -DAYS_CCSDS_TO_UNIX as u64);
+    }
+}

src/tm.rs

@@ -9,6 +9,7 @@ use crate::{
     CCSDS_HEADER_LEN,
 };
 use core::mem::size_of;
+#[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
 use zerocopy::AsBytes;
 
@@ -21,7 +22,7 @@ pub const PUC_TM_MIN_SEC_HEADER_LEN: usize = 7;
 pub const PUS_TM_MIN_LEN_WITHOUT_SOURCE_DATA: usize =
     CCSDS_HEADER_LEN + PUC_TM_MIN_SEC_HEADER_LEN + size_of::<CrcType>();
 
-pub trait PusTmSecondaryHeaderT {
+pub trait GenericPusTmSecondaryHeader {
     fn pus_version(&self) -> PusVersion;
     fn sc_time_ref_status(&self) -> u8;
     fn service(&self) -> u8;
@@ -31,6 +32,7 @@ pub trait PusTmSecondaryHeaderT {
 }
 
 pub mod zc {
+    use super::GenericPusTmSecondaryHeader;
     use crate::ecss::{PusError, PusVersion};
     use zerocopy::{AsBytes, FromBytes, NetworkEndian, Unaligned, U16};
 
@@ -76,7 +78,7 @@ pub mod zc {
         }
     }
 
-    impl super::PusTmSecondaryHeaderT for PusTmSecHeaderWithoutTimestamp {
+    impl GenericPusTmSecondaryHeader for PusTmSecHeaderWithoutTimestamp {
         fn pus_version(&self) -> PusVersion {
             PusVersion::try_from(self.pus_version_and_sc_time_ref_status >> 4 & 0b1111)
                 .unwrap_or(PusVersion::Invalid)
@@ -104,19 +106,20 @@ pub mod zc {
     }
 }
 
-#[derive(PartialEq, Eq, Serialize, Deserialize, Copy, Clone, Debug)]
-pub struct PusTmSecondaryHeader<'slice> {
+#[derive(PartialEq, Eq, Copy, Clone, Debug)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub struct PusTmSecondaryHeader<'stamp> {
     pus_version: PusVersion,
     pub sc_time_ref_status: u8,
     pub service: u8,
     pub subservice: u8,
     pub msg_counter: u16,
     pub dest_id: u16,
-    pub time_stamp: &'slice [u8],
+    pub time_stamp: &'stamp [u8],
 }
 
-impl<'slice> PusTmSecondaryHeader<'slice> {
-    pub fn new_simple(service: u8, subservice: u8, time_stamp: &'slice [u8]) -> Self {
+impl<'stamp> PusTmSecondaryHeader<'stamp> {
+    pub fn new_simple(service: u8, subservice: u8, time_stamp: &'stamp [u8]) -> Self {
         PusTmSecondaryHeader {
             pus_version: PusVersion::PusC,
             sc_time_ref_status: 0,
@@ -133,7 +136,7 @@ impl<'slice> PusTmSecondaryHeader<'slice> {
         subservice: u8,
         msg_counter: u16,
         dest_id: u16,
-        time_stamp: &'slice [u8],
+        time_stamp: &'stamp [u8],
     ) -> Self {
         PusTmSecondaryHeader {
             pus_version: PusVersion::PusC,
@@ -147,7 +150,7 @@ impl<'slice> PusTmSecondaryHeader<'slice> {
     }
 }
 
-impl PusTmSecondaryHeaderT for PusTmSecondaryHeader<'_> {
+impl GenericPusTmSecondaryHeader for PusTmSecondaryHeader<'_> {
     fn pus_version(&self) -> PusVersion {
         self.pus_version
     }
@@ -193,25 +196,31 @@ impl<'slice> TryFrom<zc::PusTmSecHeader<'slice>> for PusTmSecondaryHeader<'slice
 /// structure to generate the raw byte representation of PUS telemetry or to
 /// deserialize from one from raw bytes.
 ///
-/// This class also derives the [serde::Serialize] and [serde::Deserialize] trait which allows
-/// to send around TM packets in a raw byte format using a serde provider like
-/// [postcard](https://docs.rs/postcard/latest/postcard/).
+/// This class also derives the [serde::Serialize] and [serde::Deserialize] trait if the [serde]
+/// feature is used which allows to send around TM packets in a raw byte format using a serde
+/// provider like [postcard](https://docs.rs/postcard/latest/postcard/).
 ///
 /// There is no spare bytes support yet.
-#[derive(PartialEq, Eq, Serialize, Deserialize, Debug, Copy, Clone)]
-pub struct PusTm<'slice> {
+///
+/// # Lifetimes
+///
+/// * `'src_data` - Life time of a buffer where the user provided time stamp and source data will
+///    be serialized into.
+#[derive(PartialEq, Eq, Debug, Copy, Clone)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub struct PusTm<'src_data> {
     pub sp_header: SpHeader,
-    pub sec_header: PusTmSecondaryHeader<'slice>,
+    pub sec_header: PusTmSecondaryHeader<'src_data>,
     /// If this is set to false, a manual call to [PusTm::calc_own_crc16] or
     /// [PusTm::update_packet_fields] is necessary for the serialized or cached CRC16 to be valid.
     pub calc_crc_on_serialization: bool,
-    #[serde(skip)]
-    raw_data: Option<&'slice [u8]>,
-    source_data: Option<&'slice [u8]>,
+    #[cfg_attr(feature = "serde", serde(skip))]
+    raw_data: Option<&'src_data [u8]>,
+    source_data: Option<&'src_data [u8]>,
     crc16: Option<u16>,
 }
 
-impl<'slice> PusTm<'slice> {
+impl<'src_data> PusTm<'src_data> {
     /// Generates a new struct instance.
     ///
     /// # Arguments
@@ -226,8 +235,8 @@ impl<'slice> PusTm<'slice> {
     ///     the correct value to this field manually
     pub fn new(
         sp_header: &mut SpHeader,
-        sec_header: PusTmSecondaryHeader<'slice>,
-        source_data: Option<&'slice [u8]>,
+        sec_header: PusTmSecondaryHeader<'src_data>,
+        source_data: Option<&'src_data [u8]>,
         set_ccsds_len: bool,
     ) -> Self {
         sp_header.set_packet_type(PacketType::Tm);
@@ -255,11 +264,11 @@ impl<'slice> PusTm<'slice> {
         length
     }
 
-    pub fn time_stamp(&self) -> &'slice [u8] {
+    pub fn time_stamp(&self) -> &'src_data [u8] {
         self.sec_header.time_stamp
     }
 
-    pub fn source_data(&self) -> Option<&'slice [u8]> {
+    pub fn source_data(&self) -> Option<&'src_data [u8]> {
         self.source_data
     }
 
@@ -311,7 +320,6 @@ impl<'slice> PusTm<'slice> {
     /// Write the raw PUS byte representation to a provided buffer.
     pub fn write_to_bytes(&self, slice: &mut [u8]) -> Result<usize, PusError> {
         let mut curr_idx = 0;
-        let sph_zc = crate::zc::SpHeader::from(self.sp_header);
         let total_size = self.len_packed();
         if total_size > slice.len() {
             return Err(ByteConversionError::ToSliceTooSmall(SizeMissmatch {
@@ -320,10 +328,8 @@ impl<'slice> PusTm<'slice> {
             })
             .into());
         }
-        sph_zc
-            .to_bytes(&mut slice[curr_idx..curr_idx + CCSDS_HEADER_LEN])
-            .ok_or(ByteConversionError::ZeroCopyToError)?;
-
+        self.sp_header
+            .write_to_be_bytes(&mut slice[0..CCSDS_HEADER_LEN])?;
         curr_idx += CCSDS_HEADER_LEN;
         let sec_header_len = size_of::<zc::PusTmSecHeaderWithoutTimestamp>();
         let sec_header = zc::PusTmSecHeaderWithoutTimestamp::try_from(self.sec_header).unwrap();
@@ -389,7 +395,7 @@ impl<'slice> PusTm<'slice> {
     /// the instance and the found byte length of the packet. The timestamp length needs to be
     /// known beforehand.
     pub fn from_bytes(
-        slice: &'slice [u8],
+        slice: &'src_data [u8],
         timestamp_len: usize,
     ) -> Result<(Self, usize), PusError> {
         let raw_data_len = slice.len();
@@ -397,11 +403,9 @@ impl<'slice> PusTm<'slice> {
             return Err(PusError::RawDataTooShort(raw_data_len));
         }
         let mut current_idx = 0;
-        let sph =
-            crate::zc::SpHeader::from_bytes(&slice[current_idx..current_idx + CCSDS_HEADER_LEN])
-                .ok_or(ByteConversionError::ZeroCopyFromError)?;
+        let (sp_header, _) = SpHeader::from_be_bytes(&slice[0..CCSDS_HEADER_LEN])?;
         current_idx += 6;
-        let total_len = sph.total_len();
+        let total_len = sp_header.total_len();
         if raw_data_len < total_len || total_len < PUS_TM_MIN_LEN_WITHOUT_SOURCE_DATA {
             return Err(PusError::RawDataTooShort(raw_data_len));
         }
@@ -417,7 +421,7 @@ impl<'slice> PusTm<'slice> {
         current_idx += timestamp_len;
         let raw_data = &slice[0..total_len];
         let pus_tm = PusTm {
-            sp_header: SpHeader::from(sph),
+            sp_header,
             sec_header: PusTmSecondaryHeader::try_from(zc_sec_header_wrapper).unwrap(),
             raw_data: Some(&slice[0..total_len]),
             source_data: user_data_from_raw(current_idx, total_len, raw_data_len, slice)?,
@@ -452,7 +456,7 @@ impl PusPacket for PusTm<'_> {
 }
 
 //noinspection RsTraitImplementation
-impl PusTmSecondaryHeaderT for PusTm<'_> {
+impl GenericPusTmSecondaryHeader for PusTm<'_> {
     delegate!(to self.sec_header {
         fn pus_version(&self) -> PusVersion;
         fn service(&self) -> u8;
@@ -470,13 +474,13 @@ mod tests {
     use crate::SpHeader;
 
     fn base_ping_reply_full_ctor(time_stamp: &[u8]) -> PusTm {
-        let mut sph = SpHeader::tm(0x123, 0x234, 0).unwrap();
+        let mut sph = SpHeader::tm_unseg(0x123, 0x234, 0).unwrap();
         let tc_header = PusTmSecondaryHeader::new_simple(17, 2, &time_stamp);
         PusTm::new(&mut sph, tc_header, None, true)
     }
 
     fn base_hk_reply<'a>(time_stamp: &'a [u8], src_data: &'a [u8]) -> PusTm<'a> {
-        let mut sph = SpHeader::tm(0x123, 0x234, 0).unwrap();
+        let mut sph = SpHeader::tm_unseg(0x123, 0x234, 0).unwrap();
         let tc_header = PusTmSecondaryHeader::new_simple(3, 5, &time_stamp);
         PusTm::new(&mut sph, tc_header, Some(src_data), true)
     }
@@ -548,7 +552,7 @@ mod tests {
 
     #[test]
     fn test_manual_field_update() {
-        let mut sph = SpHeader::tm(0x123, 0x234, 0).unwrap();
+        let mut sph = SpHeader::tm_unseg(0x123, 0x234, 0).unwrap();
         let tc_header = PusTmSecondaryHeader::new_simple(17, 2, dummy_time_stamp());
         let mut tm = PusTm::new(&mut sph, tc_header, None, false);
         tm.calc_crc_on_serialization = false;