ccsds length field calculation

spacepackets/src/lib.rs

@@ -10,6 +10,8 @@ pub enum PacketError {
     ToBytesSliceTooSmall(usize),
     /// The [zerocopy] library failed to write to bytes
     ToBytesZeroCopyError,
+    /// CRC16 needs to be calculated first
+    CrcCalculationMissing,
 }
 
 #[derive(Serialize, Deserialize, Debug, PartialEq, Copy, Clone)]
@@ -375,17 +377,9 @@ pub mod zc {
             ((self.version_packet_id.get() >> 13) as u8) & 0b111
         }
 
-        fn packet_id_raw(&self) -> u16 {
-            self.version_packet_id.get() & (!VERSION_MASK)
-        }
         fn packet_id(&self) -> PacketId {
             PacketId::from(self.packet_id_raw())
         }
-
-        fn psc_raw(&self) -> u16 {
-            self.psc.get()
-        }
-
         fn psc(&self) -> PacketSequenceCtrl {
             PacketSequenceCtrl::from(self.psc_raw())
         }
@@ -394,6 +388,14 @@ pub mod zc {
         fn data_len(&self) -> u16 {
             self.data_len.get()
         }
+
+        fn packet_id_raw(&self) -> u16 {
+            self.version_packet_id.get() & (!VERSION_MASK)
+        }
+
+        fn psc_raw(&self) -> u16 {
+            self.psc.get()
+        }
     }
 
     impl CcsdsPrimaryHeader for SpHeader {

spacepackets/src/tc.rs

@@ -1,7 +1,10 @@
 use std::mem::size_of;
 
+type CrcType = u16;
+/// PUS C secondary header length is fixed
+pub const PUC_TC_SECONDARY_HEADER_LEN: usize = size_of::<zc::PusTcDataFieldHeader>();
 pub const PUS_TC_MIN_LEN_WITHOUT_APP_DATA: usize =
-    size_of::<crate::zc::SpHeader>() + size_of::<zc::PusTcDataFieldHeader>();
+    size_of::<crate::zc::SpHeader>() + PUC_TC_SECONDARY_HEADER_LEN + size_of::<CrcType>();
 
 pub mod zc {
     use crate::ecss::{PusError, PusVersion};
@@ -95,10 +98,47 @@ pub mod srd {
             }
         }
 
+        pub fn len(&self) -> usize {
+            let mut length = super::PUS_TC_MIN_LEN_WITHOUT_APP_DATA;
+            if let Some(app_data) = self.app_data {
+                length += app_data.len();
+            }
+            length
+        }
+
+        /// Calculate the CCSDS space packet data length field and sets it
+        pub fn set_ccsds_data_len(&mut self) {
+            self.sph.data_len = self.len() as u16 - size_of::<crate::zc::SpHeader>() as u16 - 1;
+        }
+
+        pub fn calc_crc16(&mut self) {
+            let mut digest = CRC_CCITT_FALSE.digest();
+            let sph_zc = crate::zc::SpHeader::from(self.sph);
+            digest.update(sph_zc.as_bytes());
+            let pus_tc_header =
+                super::zc::PusTcDataFieldHeader::try_from(self.data_field_header).unwrap();
+            digest.update(pus_tc_header.as_bytes());
+            if let Some(app_data) = self.app_data {
+                digest.update(app_data);
+            }
+            self.crc16 = Some(digest.finalize())
+        }
+
+        /// This function updates two important internal fields: The CCSDS packet length in the
+        /// space packet header and the CRC16 field. This function should be called before
+        /// the TC packet is serialized
+        pub fn update_packet_fields(&mut self) {
+            self.set_ccsds_data_len();
+            self.calc_crc16();
+        }
+
         pub fn copy_to_buf(
-            &mut self,
+            &self,
             slice: &mut (impl AsMut<[u8]> + ?Sized),
         ) -> Result<usize, PacketError> {
+            if self.crc16.is_none() {
+                return Err(PacketError::CrcCalculationMissing);
+            }
             let mut_slice = slice.as_mut();
             let mut curr_idx = 0;
             let sph_zc = crate::zc::SpHeader::from(self.sph);
@@ -126,10 +166,16 @@ pub mod srd {
                 mut_slice[curr_idx..curr_idx + app_data.len()].copy_from_slice(app_data);
                 curr_idx += app_data.len();
             }
+            mut_slice[curr_idx..curr_idx + 2]
+                .copy_from_slice(self.crc16.unwrap().to_ne_bytes().as_slice());
+            curr_idx += 2;
             Ok(curr_idx)
         }
 
-        pub fn append_to_vec(&mut self, vec: &mut Vec<u8>) -> Result<usize, PacketError> {
+        pub fn append_to_vec(&self, vec: &mut Vec<u8>) -> Result<usize, PacketError> {
+            if self.crc16.is_none() {
+                return Err(PacketError::CrcCalculationMissing);
+            }
             let sph_zc = crate::zc::SpHeader::from(self.sph);
             let mut appended_len = super::PUS_TC_MIN_LEN_WITHOUT_APP_DATA;
             if let Some(app_data) = self.app_data {
@@ -143,6 +189,7 @@ pub mod srd {
             if let Some(app_data) = self.app_data {
                 vec.extend_from_slice(app_data);
             }
+            vec.extend_from_slice(self.crc16.unwrap().to_ne_bytes().as_slice());
             Ok(appended_len)
         }
     }
@@ -213,19 +260,19 @@ mod tests {
     fn test_tc() {
         let mut sph = SpHeader::tc(0x42, 12).unwrap();
         let mut pus_tc = PusTc::new(&mut sph, 1, 1, None);
-        let out = to_stdvec(&pus_tc).unwrap();
+        let _out = to_stdvec(&pus_tc).unwrap();
-        println!("Vector {:#04x?} with length {}", out, out.len());
-
         let mut test_buf = [0; 32];
+        pus_tc.update_packet_fields();
+        assert_eq!(pus_tc.len(), 13);
         let size = pus_tc
             .copy_to_buf(test_buf.as_mut_slice())
             .expect("Error writing TC to buffer");
-        println!("Test buffer: {:?} with {size} written bytes", test_buf);
+        println!("Test buffer: {:02x?} with {size} written bytes", test_buf);
 
         let mut test_vec = Vec::new();
         let size = pus_tc
             .append_to_vec(&mut test_vec)
             .expect("Error writing TC to vector");
-        println!("Test Vector: {:?} with {size} written bytes", test_vec);
+        println!("Test Vector: {:02x?} with {size} written bytes", test_vec);
     }
 }