cargo fmt

Reviewed-on: #4
Reviewed-by: Paul Nehlich <nehlichp@irs.uni-stuttgart.de>

CHANGELOG.md

@@ -8,6 +8,12 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 # [unreleased]
 
+# [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 +25,18 @@ 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 = "0.4.0"
 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

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/cds.rs

@@ -1,4 +1,4 @@
-//! Module to generate or read CDS timestamps as specified in
+//! 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.
@@ -6,7 +6,8 @@ use super::*;
 use crate::private::Sealed;
 use core::fmt::Debug;
 
-const CDS_SHORT_P_FIELD: u8 = (CcsdsTimeCodes::Cds as u8) << 4;
+/// 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
@@ -124,7 +125,7 @@ pub fn precision_from_pfield(pfield: u8) -> SubmillisPrecision {
 ///     assert_eq!(stamp_deserialized.len_as_bytes(), 7);
 /// }
 /// ```
-#[derive(Debug, Copy, Clone, Default, PartialEq, Eq)]
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub struct TimeProvider<DaysLen: ProvidesDaysLength = DaysLen16Bits> {
     pfield: u8,
@@ -338,9 +339,8 @@ impl<ProvidesDaysLen: ProvidesDaysLength> TimeProvider<ProvidesDaysLen> {
             unix_seconds: 0,
             submillis_precision: None,
         };
-        let unix_days_seconds =
-            ccsds_to_unix_days(ccsds_days.into()) as i64 * SECONDS_PER_DAY as i64;
-        provider.setup(unix_days_seconds as i64, ms_of_day.into());
+        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)
     }
 
@@ -392,7 +392,7 @@ impl<ProvidesDaysLen: ProvidesDaysLength> TimeProvider<ProvidesDaysLen> {
         day_seg_len: LengthOfDaySegment,
         submillis_prec: Option<SubmillisPrecision>,
     ) -> u8 {
-        let mut pfield = CDS_SHORT_P_FIELD | ((day_seg_len as u8) << 2);
+        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,
@@ -552,7 +552,7 @@ impl<ProvidesDaysLen: ProvidesDaysLength> CcsdsTimeProvider for TimeProvider<Pro
     }
 
     fn date_time(&self) -> Option<DateTime<Utc>> {
-        self.calc_date_time((self.ms_of_day % 1000) as u32)
+        self.calc_date_time(self.ms_of_day % 1000)
     }
 }
 

src/time/cuc.rs

@@ -1,15 +1,96 @@
+//! 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),
-    InvalidFractionWidth(u8),
+    InvalidFractionResolution(FractionalResolution),
     InvalidCounter(u8, u64),
-    InvalidFractions(u8, u64),
+    InvalidFractions(FractionalResolution, u64),
 }
 
 impl Display for CucError {
@@ -18,14 +99,14 @@ impl Display for CucError {
             CucError::InvalidCounterWidth(w) => {
                 write!(f, "invalid cuc counter byte width {}", w)
             }
-            CucError::InvalidFractionWidth(w) => {
-                write!(f, "invalid cuc fractional part 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)
+                write!(f, "invalid cuc fractional part {} for width {:?}", c, w)
             }
         }
     }
@@ -37,18 +118,51 @@ 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 provider uses the CCSDS epoch. Furthermore the preamble field only has one byte,
-/// which allows a time code representation through the year 2094.
+/// This object is the abstraction for the CCSDS Unsegmented Time Code (CUC) using the CCSDS epoch
+/// and a small preamble field.
 ///
-/// More specifically, only 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.
+/// 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<WidthCounterPair>,
+    fractions: Option<FractionalPart>,
 }
 
 #[inline]
@@ -60,24 +174,162 @@ pub fn pfield_len(pfield: u8) -> usize {
 }
 
 impl TimeProviderCcsdsEpoch {
-    fn build_p_field(counter_width: u8, fractions_width: Option<u8>) -> u8 {
-        let mut pfield = (CcsdsTimeCodes::CucCcsdsEpoch as u8) << 4;
+    /// 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) << 3;
+        pfield |= (counter_width - 1) << 2;
         if let Some(fractions_width) = fractions_width {
-            if !(1..=3).contains(&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",
+                    "invalid fractions width {:?} for cuc timestamp",
                     fractions_width
                 );
             }
-            pfield |= fractions_width;
+            pfield |= fractions_width as u8;
         }
         pfield
     }
@@ -85,14 +337,10 @@ impl TimeProviderCcsdsEpoch {
     fn update_p_field_fractions(&mut self) {
         self.pfield &= !(0b11);
         if let Some(fractions) = self.fractions {
-            self.pfield |= fractions.0;
+            self.pfield |= fractions.0 as u8;
         }
     }
 
-    pub fn len_packed(&self) -> usize {
-        Self::len_packed_from_pfield(self.pfield)
-    }
-
     #[inline]
     pub fn len_cntr_from_pfield(pfield: u8) -> u8 {
         ((pfield >> 2) & 0b11) + 1
@@ -127,8 +375,7 @@ impl TimeProviderCcsdsEpoch {
         base_len
     }
 
-    /// Verifies the raw width parameter and returns the actual length, which is the raw
-    /// value plus 1.
+    /// Verifies the raw width parameter.
     fn verify_counter_width(width: u8) -> Result<(), CucError> {
         if width == 0 || width > 4 {
             return Err(CucError::InvalidCounterWidth(width));
@@ -136,14 +383,14 @@ impl TimeProviderCcsdsEpoch {
         Ok(())
     }
 
-    fn verify_fractions_width(width: u8) -> Result<(), CucError> {
-        if width > 3 {
-            return Err(CucError::InvalidFractionWidth(width));
+    fn verify_fractions_width(width: FractionalResolution) -> Result<(), CucError> {
+        if width as u8 > 3 {
+            return Err(CucError::InvalidFractionResolution(width));
         }
         Ok(())
     }
 
-    fn verify_fractions_value(val: WidthCounterPair) -> Result<(), CucError> {
+    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));
         }
@@ -151,44 +398,6 @@ impl TimeProviderCcsdsEpoch {
     }
 }
 
-impl TimeProviderCcsdsEpoch {
-    pub fn new_default(counter: u32) -> Self {
-        // These values are definitely valid, so it is okay to unwrap here.
-        Self::new(WidthCounterPair(4, counter), None).unwrap()
-    }
-    pub fn new_u16_counter(counter: u16) -> Self {
-        // These values are definitely valid, so it is okay to unwrap here.
-        Self::new(WidthCounterPair(2, counter as u32), None).unwrap()
-    }
-
-    pub fn set_fractions(&mut self, fractions: WidthCounterPair) -> Result<(), CucError> {
-        Self::verify_fractions_width(fractions.0)?;
-        Self::verify_fractions_value(fractions)?;
-        self.fractions = Some(fractions);
-        self.update_p_field_fractions();
-        Ok(())
-    }
-
-    pub fn new(
-        counter: WidthCounterPair,
-        fractions: Option<WidthCounterPair>,
-    ) -> Result<Self, CucError> {
-        Self::verify_counter_width(counter.0)?;
-        if counter.1 > 2u32.pow(counter.0 as u32 * 8) - 1 {
-            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,
-        })
-    }
-}
-
 impl TimeReader for TimeProviderCcsdsEpoch {
     fn from_bytes(buf: &[u8]) -> Result<Self, TimestampError>
     where
@@ -202,6 +411,22 @@ impl TimeReader for TimeProviderCcsdsEpoch {
                 }),
             ));
         }
+        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 {
@@ -219,19 +444,24 @@ impl TimeReader for TimeProviderCcsdsEpoch {
             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) as u32
+                u32::from_be_bytes(tmp_buf)
             }
-            4 => u32::from_be_bytes(buf[current_idx..current_idx + 4].try_into().unwrap()) as u32,
+            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(WidthCounterPair(fractions_len, buf[current_idx] as u32)),
+                1 => {
+                    fractions = Some(FractionalPart(
+                        fractions_len.try_into().unwrap(),
+                        buf[current_idx] as u32,
+                    ))
+                }
                 2 => {
-                    fractions = Some(WidthCounterPair(
-                        fractions_len,
+                    fractions = Some(FractionalPart(
+                        fractions_len.try_into().unwrap(),
                         u16::from_be_bytes(buf[current_idx..current_idx + 2].try_into().unwrap())
                             as u32,
                     ))
@@ -239,15 +469,15 @@ impl TimeReader for TimeProviderCcsdsEpoch {
                 3 => {
                     let mut tmp_buf: [u8; 4] = [0; 4];
                     tmp_buf[1..4].copy_from_slice(&buf[current_idx..current_idx + 3]);
-                    fractions = Some(WidthCounterPair(
-                        fractions_len,
-                        u32::from_be_bytes(tmp_buf) as u32,
+                    fractions = Some(FractionalPart(
+                        fractions_len.try_into().unwrap(),
+                        u32::from_be_bytes(tmp_buf),
                     ))
                 }
                 _ => panic!("unreachable match arm"),
             }
         }
-        let provider = Self::new(WidthCounterPair(cntr_len, counter), fractions)?;
+        let provider = Self::new_generic(WidthCounterPair(cntr_len, counter), fractions)?;
         Ok(provider)
     }
 }
@@ -255,11 +485,11 @@ impl TimeReader for TimeProviderCcsdsEpoch {
 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_packed() {
+        if bytes.len() < self.len_as_bytes() {
             return Err(TimestampError::ByteConversionError(
                 ByteConversionError::ToSliceTooSmall(SizeMissmatch {
                     found: bytes.len(),
-                    expected: self.len_packed(),
+                    expected: self.len_as_bytes(),
                 }),
             ));
         }
@@ -286,10 +516,10 @@ impl TimeWriter for TimeProviderCcsdsEpoch {
         current_idx += self.counter.0 as usize;
         if let Some(fractions) = self.fractions {
             match fractions.0 {
-                1 => bytes[current_idx] = fractions.1 as u8,
-                2 => bytes[current_idx..current_idx + 2]
+                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()),
-                3 => bytes[current_idx..current_idx + 3]
+                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"),
@@ -299,3 +529,422 @@ impl TimeWriter for TimeProviderCcsdsEpoch {
         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

@@ -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")]
@@ -73,7 +72,7 @@ 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)
     }
 }
@@ -163,6 +162,16 @@ 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: 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 {
@@ -218,4 +227,17 @@ 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());
+        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

@@ -108,18 +108,18 @@ 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 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,
@@ -136,7 +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,
@@ -201,21 +201,26 @@ 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 +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);
@@ -259,11 +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
     }
 
@@ -390,7 +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();