some more doc fixes

Reviewed-on: #11

.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 +8,87 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 # [unreleased]
 
+The timestamp of `PusTm` is now optional. See Added and Changed section for details.
+
+## Added
+
+- `PusTmSecondaryHeader`: New `new_simple_no_timestamp` API to create secondary header without
+  timestamp.
+- `PusTm`: Add `new_simple_no_timestamp` method to create TM without timestamp
+- New `UnixTimestamp` abstraction which contains the unix seconds as an `i64`
+  and an optional subsecond millisecond counter (`u16`)
+- `MS_PER_DAY` constant.
+- CUC: Added `from_date_time` and `from_unix_stamp` constructors for time provider.
+- CUC: Add `Add<Duration>` and `AddAssign<Duration>` impl for time provider.
+
+### CDS time module
+
+- Implement `Add<Duration>` and `AddAssign<Duration>` for time providers, which allows
+  easily adding offsets to the providers.
+- Implement `TryFrom<DateTime<Utc>>` for time providers.
+- `get_dyn_time_provider_from_bytes`: Requires `alloc` support and returns
+  the correct `TimeProvider` instance wrapped as a boxed trait object
+  `Box<DynCdsTimeProvider>` by checking the length of days field.
+- Added constructor function to create the time provider
+  from `chrono::DateTime<Utc>` and a generic UNIX timestamp (`i64` seconds
+  and subsecond milliseconds).
+- `MAX_DAYS_24_BITS` which contains maximum value which can be supplied
+  to the days field of a CDS time provider with 24 bits days field width.
+- New `CdsTimestamp` trait which encapsulates common fields for all CDS time providers.
+- `from_unix_secs_with_u24_days` and `from_unix_secs_with_u16_days` which create
+   the time provider from a `UnixTimestamp` reference.
+- `from_dt_with_u16_days`, `from_dt_with_u24_days` and their `..._us_precision` and
+   `..._ps_precision` variants which allow to create time providers from
+   a `chrono::DateTime<Utc>`.
+- Add `from_bytes_with_u24_days` and `from_bytes_with_u16_days` associated methods
+
+## Changed
+
+
+- (breaking) `unix_epoch_to_ccsds_epoch`: Expect and return `i64` instead of `u64` now.
+- (breaking) `ccsds_epoch_to_unix_epoch`: Expect and return `i64` instead of `u64` now.
+- (breaking) `PusTmSecondaryHeader`: Timestamp is optional now, which translates to a
+  timestamp of size 0.
+- (breaking): `PusTm`: Renamed `time_stamp` method to `timestamp`, also returns
+  `Optional<&'src_data [u8]>` now.
+- (breaking): `PusTmSecondaryHeader`: Renamed `time_stamp` field to `timestamp` for consistency.
+- (breaking): Renamed `from_now_with_u24_days_and_us_prec` to `from_now_with_u24_days_us_precision`.
+  Also did the same for the `u16` variant.
+- (breaking): Renamed `from_now_with_u24_days_and_ps_prec` to `from_now_with_u24_days_ps_precision`.
+  Also did the same for the `u16` variant.
+- `CcsdsTimeProvider` trait (breaking):
+  - Add new `unix_stamp` method returning the new `UnixTimeStamp` struct.
+  - Add new  `subsecond_millis` method returning counter `Option<u16>`.
+  - Default impl for `unix_stamp` which re-uses `subsecond_millis` and
+    existing `unix_seconds` method.
+- `TimestampError` (breaking): Add `DateBeforeCcsdsEpoch` error type
+  because new CDS API allow supplying invalid date times before CCSDS epoch.
+  Make `TimestampError` with `#[non_exhaustive]` attribute to prevent
+  future breakages if new error variants are added.
+
+# [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.
@@ -19,11 +100,18 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
   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.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "spacepackets"
-version = "0.3.1"
+version = "0.5.0"
 edition = "2021"
 rust-version = "1.60"
 authors = ["Robin Mueller <muellerr@irs.uni-stuttgart.de>"]
@@ -14,11 +14,11 @@ 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"]
@@ -35,9 +35,9 @@ default-features = false
 version = "1.0"
 
 [features]
-default = ["std", "dep:serde"]
+default = ["std"]
 std = ["chrono/std", "chrono/clock", "alloc"]
-serde = ["chrono/serde"]
+serde = ["dep:serde", "chrono/serde"]
 alloc = ["postcard/alloc", "chrono/alloc"]
 
 [package.metadata.docs.rs]

README.md

@@ -15,7 +15,9 @@ 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
+- 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)
@@ -28,12 +30,15 @@ It also offers optional support for [`serde`](https://serde.rs/). This allows se
 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

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

@@ -15,6 +15,21 @@ 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, Debug)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
@@ -38,6 +53,7 @@ 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 {
@@ -55,6 +71,38 @@ 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 {
@@ -112,6 +160,8 @@ impl From<ByteConversionError> for PusError {
     }
 }
 
+/// 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;
 
@@ -286,13 +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

@@ -9,9 +9,11 @@
 //!    [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)
-//!  - Some helper types and functions to support ASCII timecodes ad specified in
+//!  - 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
@@ -22,12 +24,15 @@
 //! 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
 //!
@@ -124,6 +129,7 @@ impl Display for ByteConversionError {
 #[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 {
@@ -172,6 +178,8 @@ impl TryFrom<u8> for SequenceFlags {
     }
 }
 
+/// 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 {
@@ -255,6 +263,8 @@ impl From<u16> for PacketId {
     }
 }
 
+/// 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 {

src/tc.rs

@@ -215,19 +215,19 @@ impl PusTcSecondaryHeader {
 /// There is no spare bytes support yet.
 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
-pub struct PusTc<'slice> {
+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,
     #[cfg_attr(feature = "serde", serde(skip))]
-    raw_data: Option<&'slice [u8]>,
-    app_data: Option<&'slice [u8]>,
+    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
@@ -243,7 +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);
@@ -268,7 +268,7 @@ impl<'slice> PusTc<'slice> {
         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(
@@ -279,6 +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 {
@@ -401,7 +405,7 @@ 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> {
+    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));
@@ -431,7 +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
     }
 }

src/time/ascii.rs

@@ -3,8 +3,10 @@
 //! See [chrono::DateTime::format] for a usage example of the generated
 //! [chrono::format::DelayedFormat] structs.
 #[cfg(feature = "alloc")]
-use chrono::format::{DelayedFormat, StrftimeItems};
-use chrono::{DateTime, Utc};
+use chrono::{
+    format::{DelayedFormat, StrftimeItems},
+    DateTime, Utc,
+};
 
 /// Tuple of format string and formatted size for time code A.
 ///

src/time/mod.rs

@@ -7,7 +7,6 @@ use core::fmt::{Display, Formatter};
 #[cfg(not(feature = "std"))]
 use num_traits::float::FloatCore;
 
-use crate::time::cuc::CucError;
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
 #[cfg(feature = "std")]
@@ -21,6 +20,7 @@ pub mod cuc;
 
 pub const DAYS_CCSDS_TO_UNIX: i32 = -4383;
 pub const SECONDS_PER_DAY: u32 = 86400;
+pub const MS_PER_DAY: u32 = SECONDS_PER_DAY * 1000;
 
 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
@@ -56,6 +56,7 @@ pub fn ccsds_time_code_from_p_field(pfield: u8) -> Result<CcsdsTimeCodes, u8> {
 
 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+#[non_exhaustive]
 pub enum TimestampError {
     /// Contains tuple where first value is the expected time code and the second
     /// value is the found raw value
@@ -63,6 +64,7 @@ pub enum TimestampError {
     ByteConversionError(ByteConversionError),
     CdsError(cds::CdsError),
     CucError(cuc::CucError),
+    DateBeforeCcsdsEpoch(DateTime<Utc>),
     CustomEpochNotSupported,
 }
 
@@ -73,7 +75,7 @@ impl From<cds::CdsError> for TimestampError {
 }
 
 impl From<cuc::CucError> for TimestampError {
-    fn from(e: CucError) -> Self {
+    fn from(e: cuc::CucError) -> Self {
         TimestampError::CucError(e)
     }
 }
@@ -119,6 +121,9 @@ impl Display for TimestampError {
             TimestampError::ByteConversionError(e) => {
                 write!(f, "byte conversion error {}", e)
             }
+            TimestampError::DateBeforeCcsdsEpoch(e) => {
+                write!(f, "datetime with date before ccsds epoch: {}", e)
+            }
             TimestampError::CustomEpochNotSupported => {
                 write!(f, "custom epochs are not supported")
             }
@@ -163,6 +168,16 @@ 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: i64) -> i64 {
+    unix_epoch - (DAYS_CCSDS_TO_UNIX as i64 * SECONDS_PER_DAY as i64)
+}
+
+pub const fn ccsds_epoch_to_unix_epoch(ccsds_epoch: i64) -> i64 {
+    ccsds_epoch + (DAYS_CCSDS_TO_UNIX as i64 * SECONDS_PER_DAY as i64)
+}
+
 #[cfg(feature = "std")]
 #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 pub fn ms_of_day_using_sysclock() -> u32 {
@@ -190,6 +205,9 @@ pub trait TimeReader {
 }
 
 /// Trait for generic CCSDS time providers.
+///
+/// The UNIX helper methods and the [Self::date_time] method are not strictly necessary but extremely
+/// practical because they are a very common and simple exchange format for time information.
 pub trait CcsdsTimeProvider {
     fn len_as_bytes(&self) -> usize;
 
@@ -199,10 +217,99 @@ pub trait CcsdsTimeProvider {
     /// in big endian format.
     fn p_field(&self) -> (usize, [u8; 2]);
     fn ccdsd_time_code(&self) -> CcsdsTimeCodes;
+
     fn unix_seconds(&self) -> i64;
+    fn subsecond_millis(&self) -> Option<u16>;
+    fn unix_stamp(&self) -> UnixTimestamp {
+        UnixTimestamp {
+            unix_seconds: self.unix_seconds(),
+            subsecond_millis: self.subsecond_millis(),
+        }
+    }
+
     fn date_time(&self) -> Option<DateTime<Utc>>;
 }
 
+/// UNIX timestamp: Elapsed seconds since 01-01-1970 00:00:00.
+///
+/// Also can optionally include subsecond millisecond for greater accuracy.
+#[derive(Default, Debug, Copy, Clone, PartialEq, Eq)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub struct UnixTimestamp {
+    pub unix_seconds: i64,
+    subsecond_millis: Option<u16>,
+}
+
+impl UnixTimestamp {
+    /// Returns none if the subsecond millisecond value is larger than 999.
+    pub fn new(unix_seconds: i64, subsec_millis: u16) -> Option<Self> {
+        if subsec_millis > 999 {
+            return None;
+        }
+        Some(Self {
+            unix_seconds,
+            subsecond_millis: Some(subsec_millis),
+        })
+    }
+
+    pub const fn const_new(unix_seconds: i64, subsec_millis: u16) -> Self {
+        if subsec_millis > 999 {
+            panic!("subsec milliseconds exceeds 999");
+        }
+        Self {
+            unix_seconds,
+            subsecond_millis: Some(subsec_millis),
+        }
+    }
+
+    pub fn new_only_seconds(unix_seconds: i64) -> Self {
+        Self {
+            unix_seconds,
+            subsecond_millis: None,
+        }
+    }
+
+    pub fn subsecond_millis(&self) -> Option<u16> {
+        self.subsecond_millis
+    }
+
+    #[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();
+        Ok(UnixTimestamp {
+            unix_seconds: epoch as i64,
+            subsecond_millis: Some(now.subsec_millis() as u16),
+        })
+    }
+
+    #[inline]
+    pub fn unix_seconds_f64(&self) -> f64 {
+        let mut secs = self.unix_seconds as f64;
+        if let Some(subsec_millis) = self.subsecond_millis {
+            secs += subsec_millis as f64 / 1000.0;
+        }
+        secs
+    }
+
+    pub fn as_date_time(&self) -> LocalResult<DateTime<Utc>> {
+        Utc.timestamp_opt(
+            self.unix_seconds,
+            self.subsecond_millis.unwrap_or(0) as u32 * 10_u32.pow(6),
+        )
+    }
+}
+
+impl From<DateTime<Utc>> for UnixTimestamp {
+    fn from(value: DateTime<Utc>) -> Self {
+        Self {
+            unix_seconds: value.timestamp(),
+            subsecond_millis: Some(value.timestamp_subsec_millis() as u16),
+        }
+    }
+}
+
 #[cfg(all(test, feature = "std"))]
 mod tests {
     use super::*;
@@ -218,4 +325,37 @@ mod tests {
         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() as i64) as u64;
+        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);
+    }
+
+    #[test]
+    fn basic_unix_stamp_test() {
+        let stamp = UnixTimestamp::new_only_seconds(-200);
+        assert_eq!(stamp.unix_seconds, -200);
+        assert!(stamp.subsecond_millis().is_none());
+        let stamp = UnixTimestamp::new_only_seconds(250);
+        assert_eq!(stamp.unix_seconds, 250);
+        assert!(stamp.subsecond_millis().is_none());
+    }
+
+    #[test]
+    fn basic_float_unix_stamp_test() {
+        let stamp = UnixTimestamp::new(500, 600).unwrap();
+        assert!(stamp.subsecond_millis.is_some());
+        assert_eq!(stamp.unix_seconds, 500);
+        let subsec_millis = stamp.subsecond_millis().unwrap();
+        assert_eq!(subsec_millis, 600);
+        assert!((500.6 - stamp.unix_seconds_f64()).abs() < 0.0001);
+    }
 }

src/tm.rs

@@ -48,7 +48,7 @@ pub mod zc {
 
     pub struct PusTmSecHeader<'slice> {
         pub(crate) zc_header: PusTmSecHeaderWithoutTimestamp,
-        pub(crate) timestamp: &'slice [u8],
+        pub(crate) timestamp: Option<&'slice [u8]>,
     }
 
     impl TryFrom<crate::tm::PusTmSecondaryHeader<'_>> for PusTmSecHeaderWithoutTimestamp {
@@ -108,27 +108,24 @@ pub mod zc {
 
 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
-pub struct PusTmSecondaryHeader<'slice> {
+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 timestamp: Option<&'stamp [u8]>,
 }
 
-impl<'slice> PusTmSecondaryHeader<'slice> {
-    pub fn new_simple(service: u8, subservice: u8, time_stamp: &'slice [u8]) -> Self {
-        PusTmSecondaryHeader {
-            pus_version: PusVersion::PusC,
-            sc_time_ref_status: 0,
-            service,
-            subservice,
-            msg_counter: 0,
-            dest_id: 0,
-            time_stamp,
-        }
+impl<'stamp> PusTmSecondaryHeader<'stamp> {
+    pub fn new_simple(service: u8, subservice: u8, timestamp: &'stamp [u8]) -> Self {
+        Self::new(service, subservice, 0, 0, Some(timestamp))
+    }
+
+    /// Like [Self::new_simple] but without a timestamp.
+    pub fn new_simple_no_timestamp(service: u8, subservice: u8) -> Self {
+        Self::new(service, subservice, 0, 0, None)
     }
 
     pub fn new(
@@ -136,7 +133,7 @@ impl<'slice> PusTmSecondaryHeader<'slice> {
         subservice: u8,
         msg_counter: u16,
         dest_id: u16,
-        time_stamp: &'slice [u8],
+        timestamp: Option<&'stamp [u8]>,
     ) -> Self {
         PusTmSecondaryHeader {
             pus_version: PusVersion::PusC,
@@ -145,7 +142,7 @@ impl<'slice> PusTmSecondaryHeader<'slice> {
             subservice,
             msg_counter,
             dest_id,
-            time_stamp,
+            timestamp,
         }
     }
 }
@@ -187,7 +184,7 @@ impl<'slice> TryFrom<zc::PusTmSecHeader<'slice>> for PusTmSecondaryHeader<'slice
             subservice: sec_header.zc_header.subservice(),
             msg_counter: sec_header.zc_header.msg_counter(),
             dest_id: sec_header.zc_header.dest_id(),
-            time_stamp: sec_header.timestamp,
+            timestamp: sec_header.timestamp,
         })
     }
 }
@@ -201,21 +198,26 @@ impl<'slice> TryFrom<zc::PusTmSecHeader<'slice>> for PusTmSecondaryHeader<'slice
 /// provider like [postcard](https://docs.rs/postcard/latest/postcard/).
 ///
 /// There is no spare bytes support yet.
+///
+/// # 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<'slice> {
+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,
     #[cfg_attr(feature = "serde", serde(skip))]
-    raw_data: Option<&'slice [u8]>,
-    source_data: Option<&'slice [u8]>,
+    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
@@ -230,8 +232,8 @@ 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);
@@ -252,18 +254,20 @@ impl<'slice> PusTm<'slice> {
 
     pub fn len_packed(&self) -> usize {
         let mut length = PUS_TM_MIN_LEN_WITHOUT_SOURCE_DATA;
-        length += self.sec_header.time_stamp.len();
+        if let Some(timestamp) = self.sec_header.timestamp {
+            length += timestamp.len();
+        }
         if let Some(src_data) = self.source_data {
             length += src_data.len();
         }
         length
     }
 
-    pub fn time_stamp(&self) -> &'slice [u8] {
-        self.sec_header.time_stamp
+    pub fn timestamp(&self) -> Option<&'src_data [u8]> {
+        self.sec_header.timestamp
     }
 
-    pub fn source_data(&self) -> Option<&'slice [u8]> {
+    pub fn source_data(&self) -> Option<&'src_data [u8]> {
         self.source_data
     }
 
@@ -299,7 +303,9 @@ impl<'slice> PusTm<'slice> {
         digest.update(sph_zc.as_bytes());
         let pus_tc_header = zc::PusTmSecHeaderWithoutTimestamp::try_from(self.sec_header).unwrap();
         digest.update(pus_tc_header.as_bytes());
-        digest.update(self.sec_header.time_stamp);
+        if let Some(stamp) = self.sec_header.timestamp {
+            digest.update(stamp);
+        }
         if let Some(src_data) = self.source_data {
             digest.update(src_data);
         }
@@ -332,9 +338,11 @@ impl<'slice> PusTm<'slice> {
             .write_to_bytes(&mut slice[curr_idx..curr_idx + sec_header_len])
             .ok_or(ByteConversionError::ZeroCopyToError)?;
         curr_idx += sec_header_len;
-        let timestamp_len = self.sec_header.time_stamp.len();
-        slice[curr_idx..curr_idx + timestamp_len].copy_from_slice(self.sec_header.time_stamp);
-        curr_idx += timestamp_len;
+        if let Some(timestamp) = self.sec_header.timestamp {
+            let timestamp_len = timestamp.len();
+            slice[curr_idx..curr_idx + timestamp_len].copy_from_slice(timestamp);
+            curr_idx += timestamp_len;
+        }
         if let Some(src_data) = self.source_data {
             slice[curr_idx..curr_idx + src_data.len()].copy_from_slice(src_data);
             curr_idx += src_data.len();
@@ -356,8 +364,10 @@ impl<'slice> PusTm<'slice> {
     #[cfg_attr(doc_cfg, doc(cfg(feature = "alloc")))]
     pub fn append_to_vec(&self, vec: &mut Vec<u8>) -> Result<usize, PusError> {
         let sph_zc = crate::zc::SpHeader::from(self.sp_header);
-        let mut appended_len =
-            PUS_TM_MIN_LEN_WITHOUT_SOURCE_DATA + self.sec_header.time_stamp.len();
+        let mut appended_len = PUS_TM_MIN_LEN_WITHOUT_SOURCE_DATA;
+        if let Some(timestamp) = self.sec_header.timestamp {
+            appended_len += timestamp.len();
+        }
         if let Some(src_data) = self.source_data {
             appended_len += src_data.len();
         };
@@ -369,8 +379,10 @@ impl<'slice> PusTm<'slice> {
         let sec_header = zc::PusTmSecHeaderWithoutTimestamp::try_from(self.sec_header).unwrap();
         vec.extend_from_slice(sec_header.as_bytes());
         ser_len += sec_header.as_bytes().len();
-        vec.extend_from_slice(self.sec_header.time_stamp);
-        ser_len += self.sec_header.time_stamp.len();
+        if let Some(timestamp) = self.sec_header.timestamp {
+            ser_len += timestamp.len();
+            vec.extend_from_slice(timestamp);
+        }
         if let Some(src_data) = self.source_data {
             vec.extend_from_slice(src_data);
             ser_len += src_data.len();
@@ -390,7 +402,7 @@ 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();
@@ -409,9 +421,13 @@ impl<'slice> PusTm<'slice> {
         )
         .ok_or(ByteConversionError::ZeroCopyFromError)?;
         current_idx += PUC_TM_MIN_SEC_HEADER_LEN;
+        let mut timestamp = None;
+        if timestamp_len > 0 {
+            timestamp = Some(&slice[current_idx..current_idx + timestamp_len]);
+        }
         let zc_sec_header_wrapper = zc::PusTmSecHeader {
             zc_header: sec_header_zc,
-            timestamp: &slice[current_idx..current_idx + timestamp_len],
+            timestamp,
         };
         current_idx += timestamp_len;
         let raw_data = &slice[0..total_len];
@@ -468,33 +484,33 @@ mod tests {
     use crate::ecss::PusVersion::PusC;
     use crate::SpHeader;
 
-    fn base_ping_reply_full_ctor(time_stamp: &[u8]) -> PusTm {
+    fn base_ping_reply_full_ctor(timestamp: &[u8]) -> PusTm {
         let mut sph = SpHeader::tm_unseg(0x123, 0x234, 0).unwrap();
-        let tc_header = PusTmSecondaryHeader::new_simple(17, 2, &time_stamp);
+        let tc_header = PusTmSecondaryHeader::new_simple(17, 2, &timestamp);
         PusTm::new(&mut sph, tc_header, None, true)
     }
 
-    fn base_hk_reply<'a>(time_stamp: &'a [u8], src_data: &'a [u8]) -> PusTm<'a> {
+    fn base_hk_reply<'a>(timestamp: &'a [u8], src_data: &'a [u8]) -> PusTm<'a> {
         let mut sph = SpHeader::tm_unseg(0x123, 0x234, 0).unwrap();
-        let tc_header = PusTmSecondaryHeader::new_simple(3, 5, &time_stamp);
+        let tc_header = PusTmSecondaryHeader::new_simple(3, 5, &timestamp);
         PusTm::new(&mut sph, tc_header, Some(src_data), true)
     }
 
-    fn dummy_time_stamp() -> &'static [u8] {
+    fn dummy_timestamp() -> &'static [u8] {
         return &[0, 1, 2, 3, 4, 5, 6];
     }
 
     #[test]
     fn test_basic() {
-        let time_stamp = dummy_time_stamp();
-        let pus_tm = base_ping_reply_full_ctor(&time_stamp);
-        verify_ping_reply(&pus_tm, false, 22, dummy_time_stamp());
+        let timestamp = dummy_timestamp();
+        let pus_tm = base_ping_reply_full_ctor(&timestamp);
+        verify_ping_reply(&pus_tm, false, 22, dummy_timestamp());
     }
 
     #[test]
     fn test_serialization_no_source_data() {
-        let time_stamp = dummy_time_stamp();
-        let pus_tm = base_ping_reply_full_ctor(&time_stamp);
+        let timestamp = dummy_timestamp();
+        let pus_tm = base_ping_reply_full_ctor(&timestamp);
         let mut buf: [u8; 32] = [0; 32];
         let ser_len = pus_tm
             .write_to_bytes(&mut buf)
@@ -506,7 +522,7 @@ mod tests {
     #[test]
     fn test_serialization_with_source_data() {
         let src_data = [1, 2, 3];
-        let hk_reply = base_hk_reply(dummy_time_stamp(), &src_data);
+        let hk_reply = base_hk_reply(dummy_timestamp(), &src_data);
         let mut buf: [u8; 32] = [0; 32];
         let ser_len = hk_reply
             .write_to_bytes(&mut buf)
@@ -519,8 +535,8 @@ mod tests {
 
     #[test]
     fn test_setters() {
-        let time_stamp = dummy_time_stamp();
-        let mut pus_tm = base_ping_reply_full_ctor(&time_stamp);
+        let timestamp = dummy_timestamp();
+        let mut pus_tm = base_ping_reply_full_ctor(&timestamp);
         pus_tm.set_sc_time_ref_status(0b1010);
         pus_tm.set_dest_id(0x7fff);
         pus_tm.set_msg_counter(0x1f1f);
@@ -533,8 +549,8 @@ mod tests {
 
     #[test]
     fn test_deserialization_no_source_data() {
-        let time_stamp = dummy_time_stamp();
-        let pus_tm = base_ping_reply_full_ctor(&time_stamp);
+        let timestamp = dummy_timestamp();
+        let pus_tm = base_ping_reply_full_ctor(&timestamp);
         let mut buf: [u8; 32] = [0; 32];
         let ser_len = pus_tm
             .write_to_bytes(&mut buf)
@@ -542,13 +558,13 @@ mod tests {
         assert_eq!(ser_len, 22);
         let (tm_deserialized, size) = PusTm::from_bytes(&buf, 7).expect("Deserialization failed");
         assert_eq!(ser_len, size);
-        verify_ping_reply(&tm_deserialized, false, 22, dummy_time_stamp());
+        verify_ping_reply(&tm_deserialized, false, 22, dummy_timestamp());
     }
 
     #[test]
     fn test_manual_field_update() {
         let mut sph = SpHeader::tm_unseg(0x123, 0x234, 0).unwrap();
-        let tc_header = PusTmSecondaryHeader::new_simple(17, 2, dummy_time_stamp());
+        let tc_header = PusTmSecondaryHeader::new_simple(17, 2, dummy_timestamp());
         let mut tm = PusTm::new(&mut sph, tc_header, None, false);
         tm.calc_crc_on_serialization = false;
         assert_eq!(tm.data_len(), 0x00);
@@ -568,8 +584,8 @@ mod tests {
 
     #[test]
     fn test_target_buf_too_small() {
-        let time_stamp = dummy_time_stamp();
-        let pus_tm = base_ping_reply_full_ctor(&time_stamp);
+        let timestamp = dummy_timestamp();
+        let pus_tm = base_ping_reply_full_ctor(&timestamp);
         let mut buf: [u8; 16] = [0; 16];
         let res = pus_tm.write_to_bytes(&mut buf);
         assert!(res.is_err());
@@ -592,8 +608,8 @@ mod tests {
     #[test]
     #[cfg(feature = "alloc")]
     fn test_append_to_vec() {
-        let time_stamp = dummy_time_stamp();
-        let pus_tm = base_ping_reply_full_ctor(&time_stamp);
+        let timestamp = dummy_timestamp();
+        let pus_tm = base_ping_reply_full_ctor(&timestamp);
         let mut vec = Vec::new();
         let res = pus_tm.append_to_vec(&mut vec);
         assert!(res.is_ok());
@@ -605,7 +621,7 @@ mod tests {
     #[cfg(feature = "alloc")]
     fn test_append_to_vec_with_src_data() {
         let src_data = [1, 2, 3];
-        let hk_reply = base_hk_reply(dummy_time_stamp(), &src_data);
+        let hk_reply = base_hk_reply(dummy_timestamp(), &src_data);
         let mut vec = Vec::new();
         vec.push(4);
         let res = hk_reply.append_to_vec(&mut vec);
@@ -634,7 +650,7 @@ mod tests {
         assert_eq!(buf[11], 0x00);
         assert_eq!(buf[12], 0x00);
         // Timestamp
-        assert_eq!(&buf[13..20], dummy_time_stamp());
+        assert_eq!(&buf[13..20], dummy_timestamp());
         let mut digest = CRC_CCITT_FALSE.digest();
         digest.update(&buf[0..20]);
         let crc16 = digest.finalize();
@@ -646,14 +662,14 @@ mod tests {
         tm: &PusTm,
         has_user_data: bool,
         exp_full_len: usize,
-        exp_time_stamp: &[u8],
+        exp_timestamp: &[u8],
     ) {
         assert!(tm.is_tm());
         assert_eq!(PusPacket::service(tm), 17);
         assert_eq!(PusPacket::subservice(tm), 2);
         assert!(tm.sec_header_flag());
         assert_eq!(tm.len_packed(), exp_full_len);
-        assert_eq!(tm.time_stamp(), exp_time_stamp);
+        assert_eq!(tm.timestamp().unwrap(), exp_timestamp);
         if has_user_data {
             assert!(!tm.user_data().is_none());
         }