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         LsfFrame, PacketFrame, PacketFrameCounter, StreamFrame, BERT_SYNC, LSF_SYNC, PACKET_SYNC,
   7         STREAM_SYNC,
   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 }
  37
  38 impl SyncBurst {
  39     pub(crate) fn target(&self) -> [i8; 8] {
  40         match self {
  41             Self::Lsf => LSF_SYNC,
  42             Self::Bert => BERT_SYNC,
  43             Self::Stream => STREAM_SYNC,
  44             Self::Packet => PACKET_SYNC,
  45         }
  46     }
  47 }
  48
  49 const SYNC_MIN_GAIN: f32 = 16.0;
  50 const SYNC_BIT_THRESHOLD: f32 = 0.3;
  51 pub const SYNC_THRESHOLD: f32 = 100.0;
  52
  53 pub(crate) fn sync_burst_correlation(target: [i8; 8], samples: &[f32]) -> (f32, f32, f32) {
  54     let mut pos_max: f32 = f32::MIN;
  55     let mut neg_max: f32 = f32::MAX;
  56     for i in 0..8 {
  57         pos_max = pos_max.max(samples[i * 10]);
  58         neg_max = neg_max.min(samples[i * 10]);
  59     }
  60     let gain = (pos_max - neg_max) / 2.0;
  61     let shift = pos_max + neg_max;
  62     if gain < SYNC_MIN_GAIN {
  63         return (f32::MAX, gain, shift);
  64     }
  65     let mut diff = 0.0;
  66     for i in 0..8 {
  67         let sym_diff = (((samples[i * 10] - shift) / gain) - target[i] as f32).abs();
  68         if sym_diff > SYNC_BIT_THRESHOLD {
  69             return (f32::MAX, gain, shift);
  70         }
  71         diff += sym_diff;
  72     }
  73     (diff, gain, shift)
  74 }
  75
  76 /// Decode frame and return contents after the sync burst
  77 pub(crate) fn frame_initial_decode(frame: &[f32] /* length 192 */) -> [u8; 46] {
  78     let mut decoded = [0u8; 48];
  79     let mut decoded_bits = BitsMut::new(&mut decoded);
  80     for (idx, s) in frame.iter().enumerate() {
  81         let dibits = decode_sample(*s);
  82         decoded_bits.set_bit(idx * 2, dibits[0]);
  83         decoded_bits.set_bit(idx * 2 + 1, dibits[1]);
  84     }
  85     random_xor(&mut decoded[2..]);
  86     interleave(&decoded[2..])
  87 }
  88
  89 pub(crate) fn parse_lsf(frame: &[f32] /* length 192 */) -> Option<LsfFrame> {
  90     let deinterleaved = frame_initial_decode(frame);
  91     let lsf = match fec::decode(&deinterleaved, 240, p_1) {
  92         Some(lsf) => LsfFrame(lsf),
  93         None => return None,
  94     };
  95     debug!("full lsf: {:?}", lsf.0);
  96     let crc = lsf.crc();
  97     debug!("recv crc: {:04X}", crc);
  98     debug!("destination: {:?}", lsf.destination());
  99     debug!("source: {:?}", lsf.source());
 100     debug!("mode: {:?}", lsf.mode());
 101     debug!("data type: {:?}", lsf.data_type());
 102     debug!("encryption type: {:?}", lsf.encryption_type());
 103     debug!("can: {}", lsf.channel_access_number());
 104     debug!("meta: {:?}", lsf.meta());
 105     Some(lsf)
 106 }
 107
 108 pub(crate) fn try_lich_decode(type2_bits: &[u8]) -> Option<(u8, [u8; 5])> {
 109     let mut decoded = 0u64;
 110     for (input_idx, input_bytes) in type2_bits.chunks(3).enumerate() {
 111         let mut input: u32 = 0;
 112         for (idx, byte) in input_bytes.iter().enumerate() {
 113             input |= (*byte as u32) << (16 - (8 * idx));
 114         }
 115         let (val, _dist) = cai_golay::extended::decode(input)?;
 116         decoded |= (val as u64) << ((3 - input_idx) * 12);
 117     }
 118     let b = decoded.to_be_bytes();
 119     Some((b[7] >> 5, [b[2], b[3], b[4], b[5], b[6]]))
 120 }
 121
 122 pub(crate) fn parse_stream(frame: &[f32] /* length 192 */) -> Option<StreamFrame> {
 123     let deinterleaved = frame_initial_decode(frame);
 124     let stream_part = &deinterleaved[12..];
 125     let stream = match fec::decode(stream_part, 144, p_2) {
 126         Some(stream) => stream,
 127         None => return None,
 128     };
 129     let frame_num = u16::from_be_bytes([stream[0], stream[1]]);
 130     let eos = (frame_num & 0x8000) > 0;
 131     let frame_num = frame_num & 0x7fff; // higher layer has to handle wraparound
 132     debug!("frame number: {frame_num}, codec2: {:?}", &stream[2..18]);
 133
 134     if let Some((counter, part)) = try_lich_decode(&deinterleaved[0..12]) {
 135         debug!("LICH: received part {counter}");
 136         Some(StreamFrame {
 137             lich_idx: counter,
 138             lich_part: part,
 139             frame_number: frame_num,
 140             end_of_stream: eos,
 141             stream_data: stream[2..18].try_into().unwrap(),
 142         })
 143     } else {
 144         None
 145     }
 146 }
 147
 148 pub(crate) fn parse_packet(frame: &[f32] /* length 192 */) -> Option<PacketFrame> {
 149     let deinterleaved = frame_initial_decode(frame);
 150     let packet = match fec::decode(&deinterleaved, 206, p_3) {
 151         Some(packet) => packet,
 152         None => return None,
 153     };
 154     let final_frame = (packet[25] & 0x80) > 0;
 155     let number = (packet[25] >> 2) & 0x01f;
 156     let counter = if final_frame {
 157         PacketFrameCounter::FinalFrame {
 158             payload_len: number as usize,
 159         }
 160     } else {
 161         PacketFrameCounter::Frame {
 162             index: number as usize,
 163         }
 164     };
 165     Some(PacketFrame {
 166         payload: packet[0..25].try_into().unwrap(),
 167         counter,
 168     })
 169 }