code.octet-stream.net Git - m17rt/blob - m17core/src/decode.rs

   1 use crate::{
   2     bits::BitsMut,
   3     fec::{self, p_1, p_2, p_3},
   4     interleave::interleave,
   5     protocol::{
   6         BERT_SYNC, END_OF_TRANSMISSION, LSF_SYNC, LsfFrame, PACKET_SYNC, PREAMBLE, PacketFrame,
   7         PacketFrameCounter, STREAM_SYNC, StreamFrame,
   8     },
   9     random::random_xor,
  10 };
  11 use log::debug;
  12
  13 const PLUS_THREE: [u8; 2] = [0, 1];
  14 const PLUS_ONE: [u8; 2] = [0, 0];
  15 const MINUS_ONE: [u8; 2] = [1, 0];
  16 const MINUS_THREE: [u8; 2] = [1, 1];
  17
  18 fn decode_sample(sample: f32) -> [u8; 2] {
  19     if sample > 0.667 {
  20         PLUS_THREE
  21     } else if sample > 0.0 {
  22         PLUS_ONE
  23     } else if sample > -0.667 {
  24         MINUS_ONE
  25     } else {
  26         MINUS_THREE
  27     }
  28 }
  29
  30 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
  31 pub(crate) enum SyncBurst {
  32     Lsf,
  33     Bert,
  34     Stream,
  35     Packet,
  36     Preamble,
  37     EndOfTransmission,
  38 }
  39
  40 impl SyncBurst {
  41     pub(crate) fn target(&self) -> [i8; 8] {
  42         match self {
  43             Self::Lsf => LSF_SYNC,
  44             Self::Bert => BERT_SYNC,
  45             Self::Stream => STREAM_SYNC,
  46             Self::Packet => PACKET_SYNC,
  47             Self::Preamble => PREAMBLE,
  48             Self::EndOfTransmission => END_OF_TRANSMISSION,
  49         }
  50     }
  51 }
  52
  53 const SYNC_MIN_GAIN: f32 = 16.0;
  54 const SYNC_BIT_THRESHOLD: f32 = 0.3;
  55 pub const SYNC_THRESHOLD: f32 = 100.0;
  56
  57 pub(crate) fn sync_burst_correlation(target: [i8; 8], samples: &[f32]) -> (f32, f32, f32) {
  58     let mut pos_max: f32 = f32::MIN;
  59     let mut neg_max: f32 = f32::MAX;
  60     for i in 0..8 {
  61         pos_max = pos_max.max(samples[i]);
  62         neg_max = neg_max.min(samples[i]);
  63     }
  64     let gain = (pos_max - neg_max) / 2.0;
  65     let shift = pos_max + neg_max;
  66     if gain < SYNC_MIN_GAIN {
  67         return (f32::MAX, gain, shift);
  68     }
  69
  70     let mut diff = 0.0;
  71     for i in 0..8 {
  72         let sym_diff = (((samples[i] - shift) / gain) - target[i] as f32).abs();
  73         if sym_diff > SYNC_BIT_THRESHOLD {
  74             return (f32::MAX, gain, shift);
  75         }
  76         diff += sym_diff;
  77     }
  78     (diff, gain, shift)
  79 }
  80
  81 /// Decode frame and return contents after the sync burst
  82 pub(crate) fn frame_initial_decode(frame: &[f32] /* length 192 */) -> [u8; 46] {
  83     let mut decoded = [0u8; 48];
  84     let mut decoded_bits = BitsMut::new(&mut decoded);
  85     for (idx, s) in frame.iter().enumerate() {
  86         let dibits = decode_sample(*s);
  87         decoded_bits.set_bit(idx * 2, dibits[0]);
  88         decoded_bits.set_bit(idx * 2 + 1, dibits[1]);
  89     }
  90     random_xor(&mut decoded[2..]);
  91     interleave(&decoded[2..])
  92 }
  93
  94 pub(crate) fn parse_lsf(frame: &[f32] /* length 192 */) -> Option<(LsfFrame, u8)> {
  95     let deinterleaved = frame_initial_decode(frame);
  96     debug!("deinterleaved: {:?}", deinterleaved);
  97     let (lsf, errors) = match fec::decode(&deinterleaved, 240, p_1) {
  98         Some((lsf, errors)) => (LsfFrame(lsf), errors),
  99         None => return None,
 100     };
 101     debug!("full lsf: {:?}", lsf.0);
 102     let crc = lsf.check_crc();
 103     debug!("recv crc: {:04X}", crc);
 104     debug!("destination: {:?}", lsf.destination());
 105     debug!("source: {:?}", lsf.source());
 106     debug!("mode: {:?}", lsf.mode());
 107     debug!("data type: {:?}", lsf.data_type());
 108     debug!("encryption type: {:?}", lsf.encryption_type());
 109     debug!("can: {}", lsf.channel_access_number());
 110     debug!("meta: {:?}", lsf.meta());
 111     Some((lsf, errors))
 112 }
 113
 114 pub(crate) fn parse_stream(frame: &[f32] /* length 192 */) -> Option<(StreamFrame, u8)> {
 115     let deinterleaved = frame_initial_decode(frame);
 116     let stream_part = &deinterleaved[12..];
 117     let (stream, errors) = fec::decode(stream_part, 144, p_2)?;
 118     let frame_num = u16::from_be_bytes([stream[0], stream[1]]);
 119     let eos = (frame_num & 0x8000) > 0;
 120     let frame_num = frame_num & 0x7fff; // higher layer has to handle wraparound
 121     debug!("frame number: {frame_num}, codec2: {:?}", &stream[2..18]);
 122
 123     if let Some((counter, part)) = decode_lich(&deinterleaved[0..12]) {
 124         debug!(
 125             "LICH: received part {counter} part {part:?} from raw {:?}",
 126             &deinterleaved[0..12]
 127         );
 128         Some((
 129             StreamFrame {
 130                 lich_idx: counter,
 131                 lich_part: part,
 132                 frame_number: frame_num,
 133                 end_of_stream: eos,
 134                 stream_data: stream[2..18].try_into().unwrap(),
 135             },
 136             errors,
 137         ))
 138     } else {
 139         None
 140     }
 141 }
 142
 143 pub(crate) fn parse_packet(frame: &[f32] /* length 192 */) -> Option<(PacketFrame, u8)> {
 144     let deinterleaved = frame_initial_decode(frame);
 145     let (packet, errors) = fec::decode(&deinterleaved, 206, p_3)?;
 146     let final_frame = (packet[25] & 0x80) > 0;
 147     let number = (packet[25] >> 2) & 0x1f;
 148     let counter = if final_frame {
 149         PacketFrameCounter::FinalFrame {
 150             payload_len: number as usize,
 151         }
 152     } else {
 153         PacketFrameCounter::Frame {
 154             index: number as usize,
 155         }
 156     };
 157     Some((
 158         PacketFrame {
 159             payload: packet[0..25].try_into().unwrap(),
 160             counter,
 161         },
 162         errors,
 163     ))
 164 }
 165
 166 pub(crate) fn decode_lich(type2_bits: &[u8]) -> Option<(u8, [u8; 5])> {
 167     let mut decoded = 0u64;
 168     for (input_idx, input_bytes) in type2_bits.chunks(3).enumerate() {
 169         let mut input: u32 = 0;
 170         for (idx, byte) in input_bytes.iter().enumerate() {
 171             input |= (*byte as u32) << (16 - (8 * idx));
 172         }
 173         let (val, _dist) = cai_golay::extended::decode(input)?;
 174         decoded |= (val as u64) << ((3 - input_idx) * 12);
 175     }
 176     let b = decoded.to_be_bytes();
 177     Some((b[7] >> 5, [b[2], b[3], b[4], b[5], b[6]]))
 178 }
 179
 180 #[cfg(test)]
 181 mod tests {
 182     use super::*;
 183
 184     #[test]
 185     fn test_lich_decode() {
 186         let input = [221, 82, 162, 16, 85, 200, 5, 14, 254, 4, 13, 153];
 187         let expected_counter = 2;
 188         let expected_part = [221, 81, 5, 5, 0];
 189         assert_eq!(decode_lich(&input), Some((expected_counter, expected_part)));
 190     }
 191 }