added first PusTm impl

src/ecss.rs

@@ -3,6 +3,8 @@ use core::mem::size_of;
 use crc::{Crc, CRC_16_IBM_3740};
 use serde::{Deserialize, Serialize};
 
+pub type CrcType = u16;
+
 /// CRC algorithm used by the PUS standard
 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>();
@@ -13,6 +15,20 @@ pub enum PusVersion {
     EsaPus = 0,
     PusA = 1,
     PusC = 2,
+    Invalid = 0b1111,
+}
+
+impl TryFrom<u8> for PusVersion {
+    type Error = ();
+
+    fn try_from(value: u8) -> Result<Self, Self::Error> {
+        match value {
+            x if x == PusVersion::EsaPus as u8 => Ok(PusVersion::EsaPus),
+            x if x == PusVersion::PusA as u8 => Ok(PusVersion::PusA),
+            x if x == PusVersion::PusC as u8 => Ok(PusVersion::PusC),
+            _ => Err(()),
+        }
+    }
 }
 
 #[derive(Debug, Copy, Clone, PartialEq)]
@@ -29,9 +45,47 @@ pub enum PusError {
 pub trait PusPacket: CcsdsPacket {
     const PUS_VERSION: PusVersion = PusVersion::PusC;
 
+    fn pus_version(&self) -> PusVersion;
     fn service(&self) -> u8;
     fn subservice(&self) -> u8;
 
     fn user_data(&self) -> Option<&[u8]>;
     fn crc16(&self) -> Option<u16>;
 }
+
+pub(crate) fn crc_from_raw_data(raw_data: Option<&[u8]>) -> Result<u16, PusError> {
+    if let Some(raw_data) = raw_data {
+        if raw_data.len() < 2 {
+            return Err(PusError::RawDataTooShort(raw_data.len()));
+        }
+        return Ok(u16::from_be_bytes(
+            raw_data[raw_data.len() - 2..raw_data.len()]
+                .try_into()
+                .unwrap(),
+        ));
+    }
+    Err(PusError::NoRawData)
+}
+
+pub(crate) fn calc_pus_crc16(bytes: &[u8]) -> u16 {
+    let mut digest = CRC_CCITT_FALSE.digest();
+    digest.update(bytes);
+    digest.finalize()
+}
+
+pub(crate) fn crc_procedure(
+    calc_on_serialization: bool,
+    cached_crc16: &Option<u16>,
+    curr_idx: usize,
+    slice: &[u8],
+) -> Result<u16, PusError> {
+    let crc16;
+    if calc_on_serialization {
+        crc16 = calc_pus_crc16(&slice[0..curr_idx])
+    } else if cached_crc16.is_none() {
+        return Err(PusError::CrcCalculationMissing);
+    } else {
+        crc16 = cached_crc16.unwrap();
+    }
+    Ok(crc16)
+}