Merge branch 'main' of https://egit.irs.uni-stuttgart.de/rust/spacepackets

CHANGELOG.md

@@ -33,6 +33,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
   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.

src/ecss.rs

@@ -264,6 +264,14 @@ pub trait ToBeBytes {
     fn to_be_bytes(&self) -> Self::ByteArray;
 }
 
+impl ToBeBytes for () {
+    type ByteArray = [u8; 0];
+
+    fn to_be_bytes(&self) -> Self::ByteArray {
+        []
+    }
+}
+
 impl ToBeBytes for u8 {
     type ByteArray = [u8; 1];
 

src/time/ascii.rs

@@ -0,0 +1,128 @@
+//! Module to generate the ASCII timecodes specified in
+//! [CCSDS 301.0-B-4](https://public.ccsds.org/Pubs/301x0b4e1.pdf) section 3.5 .
+//! See [chrono::DateTime::format] for a usage example of the generated
+//! [chrono::format::DelayedFormat] structs.
+#[cfg(feature = "alloc")]
+use chrono::format::{DelayedFormat, StrftimeItems};
+use chrono::{DateTime, Utc};
+
+/// Tuple of format string and formatted size for time code A.
+///
+/// Format: YYYY-MM-DDThh:mm:ss.ddd
+///
+/// Three digits are used for the decimal fraction
+pub const FMT_STR_CODE_A_WITH_SIZE: (&str, usize) = ("%FT%T%.3f", 23);
+/// Tuple of format string and formatted size for time code A.
+///
+///  Format: YYYY-MM-DDThh:mm:ss.dddZ
+///
+/// Three digits are used for the decimal fraction and a terminator is added at the end.
+pub const FMT_STR_CODE_A_TERMINATED_WITH_SIZE: (&str, usize) = ("%FT%T%.3fZ", 24);
+
+/// Tuple of format string and formatted size for time code A.
+///
+/// Format: YYYY-DDDThh:mm:ss.ddd
+///
+/// Three digits are used for the decimal fraction
+pub const FMT_STR_CODE_B_WITH_SIZE: (&str, usize) = ("%Y-%jT%T%.3f", 21);
+/// Tuple of format string and formatted size for time code A.
+///
+/// Format: YYYY-DDDThh:mm:ss.dddZ
+///
+/// Three digits are used for the decimal fraction and a terminator is added at the end.
+pub const FMT_STR_CODE_B_TERMINATED_WITH_SIZE: (&str, usize) = ("%Y-%jT%T%.3fZ", 22);
+
+/// Generates a time code formatter using the [FMT_STR_CODE_A_WITH_SIZE] format.
+#[cfg(feature = "alloc")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "alloc")))]
+pub fn generate_time_code_a(date: &DateTime<Utc>) -> DelayedFormat<StrftimeItems<'static>> {
+    date.format(FMT_STR_CODE_A_WITH_SIZE.0)
+}
+
+/// Generates a time code formatter using the [FMT_STR_CODE_A_TERMINATED_WITH_SIZE] format.
+#[cfg(feature = "alloc")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "alloc")))]
+pub fn generate_time_code_a_terminated(
+    date: &DateTime<Utc>,
+) -> DelayedFormat<StrftimeItems<'static>> {
+    date.format(FMT_STR_CODE_A_TERMINATED_WITH_SIZE.0)
+}
+
+/// Generates a time code formatter using the [FMT_STR_CODE_B_WITH_SIZE] format.
+#[cfg(feature = "alloc")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "alloc")))]
+pub fn generate_time_code_b(date: &DateTime<Utc>) -> DelayedFormat<StrftimeItems<'static>> {
+    date.format(FMT_STR_CODE_B_WITH_SIZE.0)
+}
+
+/// Generates a time code formatter using the [FMT_STR_CODE_B_TERMINATED_WITH_SIZE] format.
+#[cfg(feature = "alloc")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "alloc")))]
+pub fn generate_time_code_b_terminated(
+    date: &DateTime<Utc>,
+) -> DelayedFormat<StrftimeItems<'static>> {
+    date.format(FMT_STR_CODE_B_TERMINATED_WITH_SIZE.0)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use chrono::Utc;
+    use std::format;
+
+    #[test]
+    fn test_ascii_timestamp_a_unterminated() {
+        let date = Utc::now();
+        let stamp_formatter = generate_time_code_a(&date);
+        let stamp = format!("{}", stamp_formatter);
+        let t_sep = stamp.find("T");
+        assert!(t_sep.is_some());
+        assert_eq!(t_sep.unwrap(), 10);
+        assert_eq!(stamp.len(), FMT_STR_CODE_A_WITH_SIZE.1);
+    }
+
+    #[test]
+    fn test_ascii_timestamp_a_terminated() {
+        let date = Utc::now();
+        let stamp_formatter = generate_time_code_a_terminated(&date);
+        let stamp = format!("{}", stamp_formatter);
+        let t_sep = stamp.find("T");
+        assert!(t_sep.is_some());
+        assert_eq!(t_sep.unwrap(), 10);
+        let z_terminator = stamp.find("Z");
+        assert!(z_terminator.is_some());
+        assert_eq!(
+            z_terminator.unwrap(),
+            FMT_STR_CODE_A_TERMINATED_WITH_SIZE.1 - 1
+        );
+        assert_eq!(stamp.len(), FMT_STR_CODE_A_TERMINATED_WITH_SIZE.1);
+    }
+
+    #[test]
+    fn test_ascii_timestamp_b_unterminated() {
+        let date = Utc::now();
+        let stamp_formatter = generate_time_code_b(&date);
+        let stamp = format!("{}", stamp_formatter);
+        let t_sep = stamp.find("T");
+        assert!(t_sep.is_some());
+        assert_eq!(t_sep.unwrap(), 8);
+        assert_eq!(stamp.len(), FMT_STR_CODE_B_WITH_SIZE.1);
+    }
+
+    #[test]
+    fn test_ascii_timestamp_b_terminated() {
+        let date = Utc::now();
+        let stamp_formatter = generate_time_code_b_terminated(&date);
+        let stamp = format!("{}", stamp_formatter);
+        let t_sep = stamp.find("T");
+        assert!(t_sep.is_some());
+        assert_eq!(t_sep.unwrap(), 8);
+        let z_terminator = stamp.find("Z");
+        assert!(z_terminator.is_some());
+        assert_eq!(
+            z_terminator.unwrap(),
+            FMT_STR_CODE_B_TERMINATED_WITH_SIZE.1 - 1
+        );
+        assert_eq!(stamp.len(), FMT_STR_CODE_B_TERMINATED_WITH_SIZE.1);
+    }
+}

src/time/cds.rs

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

src/time/cuc.rs

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

src/time/mod.rs

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