dsd-fme/src/m17.c

/*-------------------------------------------------------------------------------
 * m17.c
 * M17 Decoder (WIP)
 *
 * m17_scramble Bit Array from SDR++
 * CRC16 from M17-Implementations (thanks again, sp5wwp)
 *
 * LWVMOBILE
 * 2023-07 DSD-FME Florida Man Edition
 *-----------------------------------------------------------------------------*/
#include "dsd.h"

//try to find a fancy lfsr or calculation for this and not an array if possible
uint8_t m17_scramble[369] = { 
1, 1, 0, 1, 0, 1, 1, 0, 1, 0, 1, 1, 0, 1, 0, 1,
1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0,
1, 0, 0, 0, 0, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1,
1, 0, 0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 1, 0,
1, 0, 1, 1, 1, 0, 1, 0, 0, 1, 0, 0, 1, 1, 1, 0,
1, 0, 0, 1, 0, 1, 1, 0, 1, 0, 0, 1, 0, 0, 0, 0,
1, 1, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0,
1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1,
0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0,
0, 1, 0, 1, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1,
1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 1, 1, 0, 1,
1, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 1, 1, 1, 0,
0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 1, 1, 1,
0, 0, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 1, 0, 1, 0,
0, 0, 0, 1, 0, 1, 0, 0, 1, 1, 1, 0, 1, 0, 1, 0,
1, 1, 0, 0, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 1, 0,
0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 1, 1, 0, 1,
1, 1, 0, 1, 0, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0,
1, 1, 0, 1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 1,
1, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 1, 1,
0, 1, 0, 1, 0, 1, 1, 1, 0, 0, 0, 1, 1, 0, 0, 0,
0, 0, 1, 0, 1, 1, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1,
0, 1, 1, 1, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1 
};

char b40[] = " ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-/.";

uint8_t p1[62] = {
1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1,
1, 0, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1,
0, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1
};

//from M17_Implementations -- sp5wwp -- should have just looked here to begin with
//this setup looks very similar to the OP25 variant of crc16, but with a few differences (uses packed bytes)
uint16_t crc16m17(const uint8_t *in, const uint16_t len)
{
  uint32_t crc = 0xFFFF; //init val
  uint16_t poly = 0x5935;
  for(uint16_t i=0; i<len; i++)
  {
    crc^=in[i]<<8;
    for(uint8_t j=0; j<8; j++)
    {
      crc<<=1;
      if(crc&0x10000)
        crc=(crc^poly)&0xFFFF;
    }
  }

  return crc&(0xFFFF);
}

void M17decodeCSD(dsd_state * state, unsigned long long int dst, unsigned long long int src)
{
  //evaluate dst and src, and determine if they need to be converted to calsign
  int i, j;
  char c;
  unsigned long long int value;

  if (dst == 0xFFFFFFFFFFFF) 
    fprintf (stderr, " DST: BROADCAST");
  else if (dst == 0)
    fprintf (stderr, " DST: RESERVED %012llx", dst);
  else if (dst >= 0xEE6B28000000)
    fprintf (stderr, " DST: RESERVED %012llx", dst);
  else
  {
    fprintf (stderr, " DST: ");
    for (i = 0; i < 9; i++)
    {
      c = b40[dst % 40];
      state->m17_dst_csd[i] = c;
      fprintf (stderr, "%c", c);
      dst = dst / 40;
    }
    //assign completed CSD to a more useful string instead
    sprintf (state->m17_dst_str, "%c%c%c%c%c%c%c%c%c", 
    state->m17_dst_csd[0], state->m17_dst_csd[1], state->m17_dst_csd[2], state->m17_dst_csd[3], 
    state->m17_dst_csd[4], state->m17_dst_csd[5], state->m17_dst_csd[6], state->m17_dst_csd[7], state->m17_dst_csd[8]);

    //debug
    // fprintf (stderr, "DT: %s", state->m17_dst_str);
  }

  if (src == 0xFFFFFFFFFFFF) 
    fprintf (stderr, " SRC:  UNKNOWN FFFFFFFFFFFF");
  else if (src == 0)
    fprintf (stderr, " SRC: RESERVED %012llx", src);
  else if (src >= 0xEE6B28000000)
    fprintf (stderr, " SRC: RESERVED %012llx", src);
  else
  {
    fprintf (stderr, " SRC: ");
    for (i = 0; i < 9; i++)
    {
      c = b40[src % 40];
      state->m17_src_csd[i] = c;
      fprintf (stderr, "%c", c);
      src = src / 40;
    }
    //assign completed CSD to a more useful string instead
    sprintf (state->m17_src_str, "%c%c%c%c%c%c%c%c%c", 
    state->m17_src_csd[0], state->m17_src_csd[1], state->m17_src_csd[2], state->m17_src_csd[3], 
    state->m17_src_csd[4], state->m17_src_csd[5], state->m17_src_csd[6], state->m17_src_csd[7], state->m17_src_csd[8]);

    //debug
    // fprintf (stderr, "ST: %s", state->m17_src_str);
  }

  //debug
  // fprintf (stderr, " DST: %012llX SRC: %012llX", state->m17_dst, state->m17_src);

}

void M17decodeLSF(dsd_state * state)
{
  int i;
  
  unsigned long long int lsf_dst = (unsigned long long int)ConvertBitIntoBytes(&state->m17_lsf[0], 48);
  unsigned long long int lsf_src = (unsigned long long int)ConvertBitIntoBytes(&state->m17_lsf[48], 48);
  uint16_t lsf_type = (uint16_t)ConvertBitIntoBytes(&state->m17_lsf[96], 16);

  //this is the way the manual/code expects you to read these bits
  uint8_t lsf_ps = (lsf_type >> 0) & 0x1;
  uint8_t lsf_dt = (lsf_type >> 1) & 0x3;
  uint8_t lsf_et = (lsf_type >> 3) & 0x3;
  uint8_t lsf_es = (lsf_type >> 5) & 0x3;
  uint8_t lsf_cn = (lsf_type >> 7) & 0xF;
  uint8_t lsf_rs = (lsf_type >> 11) & 0x1F;

  //store this so we can reference it for playing voice and/or decoding data, dst/src etc
  state->m17_str_dt = lsf_dt;
  state->m17_dst = lsf_dst;
  state->m17_src = lsf_src;

  fprintf (stderr, "\n");

  //packet or stream
  if (lsf_ps == 0) fprintf (stderr, " P-");
  if (lsf_ps == 1) fprintf (stderr, " S-");

  fprintf (stderr, " CAN: %d", lsf_cn);
  M17decodeCSD(state, lsf_dst, lsf_src);

  if (lsf_et != 0) fprintf (stderr, " ENC");
  
  if (lsf_dt == 0) fprintf (stderr, " Reserved");
  if (lsf_dt == 1) fprintf (stderr, " Data");
  if (lsf_dt == 2) fprintf (stderr, " Voice (3200bps)");
  if (lsf_dt == 3) fprintf (stderr, " Voice + Data");

  if (lsf_rs != 0) fprintf (stderr, " RS: %02X", lsf_rs);

  if (lsf_et == 1) fprintf (stderr, " AES-CTR");
  if (lsf_et == 2) fprintf (stderr, " Scrambler - %d", lsf_es);

  state->m17_enc = lsf_et;
  state->m17_enc_st = lsf_es;

  //pack meta bits into 14 bytes
  for (i = 0; i < 14; i++)
    state->m17_meta[i] = (uint8_t)ConvertBitIntoBytes(&state->m17_lsf[(i*8)+112], 8);

  //Examine the Meta data
  if (lsf_et == 0 && state->m17_meta[0] != 0) //not sure if this applies universally, or just to text data byte 0 for null data
  {
    fprintf (stderr,  " Meta:");
    if (lsf_es == 0) fprintf (stderr, " Text Data");
    if (lsf_es == 1) fprintf (stderr, " GNSS Pos");
    if (lsf_es == 2) fprintf (stderr, " Extended CSD");
    if (lsf_es == 3) fprintf (stderr, " Reserved");
  }
  
  if (lsf_et == 1)
  {
    fprintf (stderr, " IV: ");
    for (i = 0; i < 14; i++)
      fprintf (stderr, "%02X", state->m17_meta[i]);
  }
  
}

int M17processLICH(dsd_state * state, dsd_opts * opts, uint8_t lich_bits[96])
{
  int i, j, err;
  err = 0;

  uint8_t lich[4][24];
  uint8_t lich_decoded[48];
  uint8_t temp[96];
  bool g[4];

  //for testing bit arrangement vs the crc code
  uint8_t bs[240];
  memset(bs, 1, sizeof(bs));

  uint16_t crc_cmp = 0;
  uint16_t crc_ext = 0;
  uint8_t crc_err = 0;

  memset(lich, 0, sizeof(lich));
  memset(lich_decoded, 0, sizeof(lich_decoded));
  memset(temp, 0, sizeof(temp));

  //execute golay 24,12 or 4 24-bit chunks and reorder into 4 12-bit chunks
  for (i = 0; i < 4; i++)
  {
    g[i] = TRUE;

    for (j = 0; j < 24; j++)
      lich[i][j] = lich_bits[(i*24)+j];

    g[i] = Golay_24_12_decode(lich[i]);
    if(g[i] == FALSE) err = -1;

    for (j = 0; j < 12; j++)
    lich_decoded[i*12+j] = lich[i][j];

  }

  uint8_t lich_counter = (uint8_t)ConvertBitIntoBytes(&lich_decoded[40], 3); //lich_cunt
  uint8_t lich_reserve = (uint8_t)ConvertBitIntoBytes(&lich_decoded[43], 5); //lich_reserved

  if (err == 0)
    fprintf (stderr, "LC: %d/6 ", lich_counter+1);
  else fprintf (stderr, "LICH G24 ERR");

  if (err = 0 && lich_reserve != 0) fprintf(stderr, " LRS: %d", lich_reserve);

  //transfer to storage
  for (i = 0; i < 40; i++)
    state->m17_lsf[lich_counter*40+i] = lich_decoded[i];

  if (opts->payload == 1)
  {
    fprintf (stderr, " LICH: ");
    for (i = 0; i < 6; i++)
      fprintf (stderr, "[%02X]", (uint8_t)ConvertBitIntoBytes(&lich_decoded[i*8], 8)); 
  }

  uint8_t lsf_packed[30];
  memset (lsf_packed, 0, sizeof(lsf_packed));

  if (lich_counter == 5)
  {

    //need to pack bytes for the sw5wwp variant of the crc (might as well, may be useful in the future)
    for (i = 0; i < 30; i++)
      lsf_packed[i] = (uint8_t)ConvertBitIntoBytes(&state->m17_lsf[i*8], 8);

    crc_cmp = crc16m17(lsf_packed, 28);
    crc_ext = (uint16_t)ConvertBitIntoBytes(&state->m17_lsf[224], 16);

    if (crc_cmp != crc_ext) crc_err = 1;

    if (crc_err == 0)
      M17decodeLSF(state);

    if (opts->payload == 1)
    {
      fprintf (stderr, "\n LSF: ");
      for (i = 0; i < 30; i++)
      {
        if (i == 15) fprintf (stderr, "\n      ");
        fprintf (stderr, "[%02X]", lsf_packed[i]);
      }
    }

    memset (state->m17_lsf, 1, sizeof(state->m17_lsf));

    //debug
    // fprintf (stderr, " E-%04X; C-%04X (CRC CHK)", crc_ext, crc_cmp);

    if (crc_err == 1) fprintf (stderr, " EMB LSF CRC ERR");
  }

  return err;
}

void M17processCodec2_1600(dsd_opts * opts, dsd_state * state, uint8_t payload[128])
{

  //If payload is the same from the stream in this mode, I suppose we could use this area to parse
  //or send off the remaining data to be handled or decoded , or just print out the raw data bytes

  int i;
  unsigned char voice1[8]; //codec2_bytes_per_frame
  unsigned char voice2[8];

  for (i = 0; i < 8; i++)
  {
    voice1[i] = (unsigned char)ConvertBitIntoBytes(&payload[i*8+0], 8);
    voice2[i] = (unsigned char)ConvertBitIntoBytes(&payload[i*8+64], 8);
  }

  //TODO: Add some decryption methods
  if (state->m17_enc != 0)
  {
    //process scrambler or AES-CTR decryption 
    //(no AES-CTR right now, Scrambler should be easy enough)
  }

  if (opts->payload == 1)
  {
    fprintf (stderr, "\n CODEC2: ");
    for (i = 0; i < 8; i++)
      fprintf (stderr, "%02X", voice1[i]);
    fprintf (stderr, " (1600)");

    fprintf (stderr, "\n LSDATA: "); //low speed data
    for (i = 0; i < 8; i++)
      fprintf (stderr, "%02X", voice2[i]);
  }
  
  #ifdef USE_CODEC2
  size_t nsam;
  nsam = 320; //codec2_samples_per_frame(state->codec2_1600);

  short samp1[nsam];
  // short samp2[nsam];
  memset (samp1, 0, sizeof(samp1));
  // memset (samp2, 0, sizeof(samp2));


  codec2_decode(state->codec2_1600, samp1, voice1);
  // codec2_decode(state->codec2_1600, samp2, voice2);


  if (opts->audio_out_type == 0 && state->m17_enc == 0)
  {
    pa_simple_write(opts->pulse_digi_dev_out, samp1, nsam*2, NULL);
    // pa_simple_write(opts->pulse_digi_dev_out, samp2, nsam*2, NULL);
  }
    
  if (opts->audio_out_type == 5 && state->m17_enc == 0)
  {
    write (opts->audio_out_fd, samp1, nsam*2);
    // write (opts->audio_out_fd, samp2, nsam*2);
  }

  //WIP: Wav file saving -- still need a way to open/close/label wav files similar to call history
  if(opts->wav_out_f != NULL && state->m17_enc == 0)
  {
    sf_write_short(opts->wav_out_f, samp1, nsam);
    // sf_write_short(opts->wav_out_f, samp2, nsam);
  }

  //TODO: Codec2 Raw file saving
  // if(mbe_out_dir)
  // {

  // }

  #endif

}

void M17processCodec2_3200(dsd_opts * opts, dsd_state * state, uint8_t payload[128])
{
  int i;
  unsigned char voice1[8]; //codec2_bytes_per_frame
  unsigned char voice2[8];

  for (i = 0; i < 8; i++)
  {
    voice1[i] = (unsigned char)ConvertBitIntoBytes(&payload[i*8+0], 8);
    voice2[i] = (unsigned char)ConvertBitIntoBytes(&payload[i*8+64], 8);
  }

  //TODO: Add some decryption methods
  if (state->m17_enc != 0)
  {
    //process scrambler or AES-CTR decryption 
    //(no AES-CTR right now, Scrambler should be easy enough)
  }

  if (opts->payload == 1)
  {
    fprintf (stderr, "\n CODEC2: ");
    for (i = 0; i < 8; i++)
      fprintf (stderr, "%02X", voice1[i]);
    fprintf (stderr, " (3200)");

    fprintf (stderr, "\n CODEC2: ");
    for (i = 0; i < 8; i++)
      fprintf (stderr, "%02X", voice2[i]);
    fprintf (stderr, " (3200)");
  }
  
  #ifdef USE_CODEC2
  size_t nsam;
  nsam = 160; //codec2_samples_per_frame(state->codec2_3200);

  short samp1[nsam];
  short samp2[nsam];
  memset (samp1, 0, sizeof(samp1));
  memset (samp2, 0, sizeof(samp2));


  codec2_decode(state->codec2_3200, samp1, voice1);
  codec2_decode(state->codec2_3200, samp2, voice2);


  if (opts->audio_out_type == 0 && state->m17_enc == 0)
  {
    pa_simple_write(opts->pulse_digi_dev_out, samp1, nsam*2, NULL);
    pa_simple_write(opts->pulse_digi_dev_out, samp2, nsam*2, NULL);
  }
    
  if (opts->audio_out_type == 5 && state->m17_enc == 0)
  {
    write (opts->audio_out_fd, samp1, nsam*2);
    write (opts->audio_out_fd, samp2, nsam*2);
  }

  //WIP: Wav file saving -- still need a way to open/close/label wav files similar to call history
  if(opts->wav_out_f != NULL && state->m17_enc == 0)
  {
    sf_write_short(opts->wav_out_f, samp1, nsam);
    sf_write_short(opts->wav_out_f, samp2, nsam);
  }

  //TODO: Codec2 Raw file saving
  // if(mbe_out_dir)
  // {

  // }

  #endif

}

void M17prepareStream(dsd_opts * opts, dsd_state * state, uint8_t m17_bits[368])
{

  int i, j, k, x; 
  uint8_t m17_punc[310]; //25 * 11 = 275
  memset (m17_punc, 0, sizeof(m17_punc));
  for (i = 0; i < 272; i++)
    m17_punc[i] = m17_bits[i+96];

  //depuncture the bits
  uint8_t m17_depunc[310]; //25 * 12 = 300
  memset (m17_depunc, 0, sizeof(m17_depunc));
  k = 0; x = 0;
  for (i = 0; i < 25; i++)
  {
    m17_depunc[k++] = m17_punc[x++];
    m17_depunc[k++] = m17_punc[x++];
    m17_depunc[k++] = m17_punc[x++];
    m17_depunc[k++] = m17_punc[x++];
    m17_depunc[k++] = m17_punc[x++];
    m17_depunc[k++] = m17_punc[x++];
    m17_depunc[k++] = m17_punc[x++];
    m17_depunc[k++] = m17_punc[x++];
    m17_depunc[k++] = m17_punc[x++];
    m17_depunc[k++] = m17_punc[x++];
    m17_depunc[k++] = m17_punc[x++];
    m17_depunc[k++] = 0; 
  }

  //setup the convolutional decoder
  uint8_t temp[300];
  uint8_t s0;
  uint8_t s1;
  uint8_t m_data[28];
  uint8_t trellis_buf[400];
  memset (trellis_buf, 0, sizeof(trellis_buf));
  memset (temp, 0, sizeof (temp));
  memset (m_data, 0, sizeof (m_data));

  for (i = 0; i < 296; i++)
    temp[i] = m17_depunc[i] << 1; 

  CNXDNConvolution_start();
  for (i = 0; i < 148; i++)
  {
    s0 = temp[(2*i)];
    s1 = temp[(2*i)+1];

    CNXDNConvolution_decode(s0, s1);
  }

  CNXDNConvolution_chainback(m_data, 144);

  //144/8 = 18, last 4 (144-148) are trailing zeroes
  for(i = 0; i < 18; i++)
  {
    trellis_buf[(i*8)+0] = (m_data[i] >> 7) & 1;
    trellis_buf[(i*8)+1] = (m_data[i] >> 6) & 1;
    trellis_buf[(i*8)+2] = (m_data[i] >> 5) & 1;
    trellis_buf[(i*8)+3] = (m_data[i] >> 4) & 1;
    trellis_buf[(i*8)+4] = (m_data[i] >> 3) & 1;
    trellis_buf[(i*8)+5] = (m_data[i] >> 2) & 1;
    trellis_buf[(i*8)+6] = (m_data[i] >> 1) & 1;
    trellis_buf[(i*8)+7] = (m_data[i] >> 0) & 1;
  }

  //load m_data into bits for either data packets or voice packets
  uint8_t payload[128];
  uint8_t end = 9;
  uint16_t fn = 0;
  memset (payload, 0, sizeof(payload));

  end = trellis_buf[0];
  fn = (uint16_t)ConvertBitIntoBytes(&trellis_buf[1], 15);

  if (opts->payload == 1)
    fprintf (stderr, " FSN: %05d", fn);

  if (end == 1)
    fprintf (stderr, " END;");

  for (i = 0; i < 128; i++)
    payload[i] = trellis_buf[i+16];

  if (state->m17_str_dt == 2)
    M17processCodec2_3200(opts, state, payload);
  else if (state->m17_str_dt == 3)
    M17processCodec2_1600(opts, state, payload);
  else if (state->m17_str_dt == 1) fprintf (stderr, " DATA;");
  else if (state->m17_str_dt == 0) fprintf (stderr, "  RES;");
  // else                             fprintf (stderr, "  UNK;");

  if (opts->payload == 1 && state->m17_str_dt < 2)
  {
    fprintf (stderr, "\n STREAM: ");
    for (i = 0; i < 18; i++) 
      fprintf (stderr, "[%02X]", (uint8_t)ConvertBitIntoBytes(&trellis_buf[i*8], 8));
  }

}

void processM17STR(dsd_opts * opts, dsd_state * state)
{

  int i, x;

  //NOTE: adding more space for dbuf seems to fix the memory issue, but I don't think this is
  //the culprit, not entirely sure what is going on here, but the issue with Cygwin (32-bit)
  //not working at all with this also is fixed by this and I can't seem to figure out why
  //its probably something really dumb that I am completely blind on seeing here for some reason

  
  uint8_t dbuf[384]; //384-bit frame - 16-bit (8 symbol) sync pattern (184 dibits)
  uint8_t m17_rnd_bits[368]; //368 bits that are still scrambled (randomized)
  uint8_t m17_int_bits[368]; //368 bits that are still interleaved
  uint8_t m17_bits[368]; //368 bits that have been de-interleaved and de-scramble
  uint8_t lich_bits[96];
  int lich_err = -1;

  memset (dbuf, 0, sizeof(dbuf));
  memset (m17_rnd_bits, 0, sizeof(m17_rnd_bits));
  memset (m17_int_bits, 0, sizeof(m17_int_bits));
  memset (m17_bits, 0, sizeof(m17_bits));
  memset (lich_bits, 0, sizeof(lich_bits));

  //load dibits into dibit buffer
  for (i = 0; i < 184; i++)
    dbuf[i] = (uint8_t) getDibit(opts, state);

  //convert dbuf into a bit array
  for (i = 0; i < 184; i++)
  {
    m17_rnd_bits[i*2+0] = (dbuf[i] >> 1) & 1;
    m17_rnd_bits[i*2+1] = (dbuf[i] >> 0) & 1;
  }

  //descramble the frame
  for (i = 0; i < 368; i++)
    m17_int_bits[i] = (m17_rnd_bits[i] ^ m17_scramble[i]) & 1;

  //deinterleave the bit array using Quadratic Permutation Polynomial
  //function π(x) = (45x + 92x^2 ) mod 368
  for (i = 0; i < 368; i++)
  {
    x = ((45*i)+(92*i*i)) % 368;
    m17_bits[i] = m17_int_bits[x];
  }

  for (i = 0; i < 96; i++)
    lich_bits[i] = m17_bits[i];

  //check lich first, and handle LSF chunk and completed LSF
  lich_err = M17processLICH(state, opts, lich_bits);

  if (lich_err == 0)
    M17prepareStream(opts, state, m17_bits);

  // if (lich_err != 0) state->lastsynctype = -1; //disable

  //ending linebreak
  fprintf (stderr, "\n");

} //end processM17STR

void processM17LSF(dsd_opts * opts, dsd_state * state)
{

  //NOTE1: Pretty sure the flow here is all correct, but the initial (and only)
  //LSF frame is demodulated incorrectly, so more than likely, this frame will
  //always be bad since there is only one sent before STR

  //NOTE2: Even with the preamble detection and LSF sync, we still get bad decode on this

  int i, j, k, x;
  uint8_t dbuf[384]; //384-bit frame - 16-bit (8 symbol) sync pattern (184 dibits)
  uint8_t m17_rnd_bits[500]; //368 bits that are still scrambled (randomized)
  uint8_t m17_int_bits[500]; //368 bits that are still interleaved
  uint8_t m17_bits[500]; //368 bits that have been de-interleaved and de-scramble
  uint8_t m17_depunc[500]; //488 bits after depuncturing

  memset (dbuf, 0, sizeof(dbuf));
  memset (m17_rnd_bits, 0, sizeof(m17_rnd_bits));
  memset (m17_int_bits, 0, sizeof(m17_int_bits));
  memset (m17_bits, 0, sizeof(m17_bits));
  memset (m17_depunc, 0, sizeof(m17_depunc));

  //load dibits into dibit buffer
  for (i = 0; i < 184; i++)
    dbuf[i] = (uint8_t) getDibit(opts, state);

  //convert dbuf into a bit array
  for (i = 0; i < 184; i++)
  {
    m17_rnd_bits[i*2+0] = (dbuf[i] >> 1) & 1;
    m17_rnd_bits[i*2+1] = (dbuf[i] >> 0) & 1;
  }

  //descramble the frame
  for (i = 0; i < 368; i++)
    m17_int_bits[i] = (m17_rnd_bits[i] ^ m17_scramble[i]) & 1;

  //deinterleave the bit array using Quadratic Permutation Polynomial
  //function π(x) = (45x + 92x^2 ) mod 368
  for (i = 0; i < 368; i++)
  {
    x = ((45*i)+(92*i*i)) % 368;
    m17_bits[i] = m17_int_bits[x];
  }

  j = 0; k = 0; x = 0;

  // P1 Depuncture
  for (i = 0; i < 488; i++)
  {
    if (p1[k++] == 1) m17_depunc[x++] = m17_bits[j++];
    else m17_depunc[x++] = 1;

    if (k == 61) k = 0; //61 -- should reset 8 times againt the array

  }

  //debug -- values seem okay at end of run
  // fprintf (stderr, "K = %d; J = %d; X = %d", k, j, x);

  //setup the convolutional decoder
  uint8_t temp[500];
  uint8_t s0;
  uint8_t s1;
  uint8_t m_data[32];
  uint8_t trellis_buf[400];
  memset (trellis_buf, 0, sizeof(trellis_buf));
  memset (temp, 0, sizeof (temp));
  memset (m_data, 0, sizeof (m_data));

  for (i = 0; i < 488; i++)
    temp[i] = m17_depunc[i] << 1; 

  CNXDNConvolution_start();
  for (i = 0; i < 244; i++)
  {
    s0 = temp[(2*i)];
    s1 = temp[(2*i)+1];

    CNXDNConvolution_decode(s0, s1);
  }

  CNXDNConvolution_chainback(m_data, 240);

  //244/8 = 30, last 4 (244-248) are trailing zeroes
  for(i = 0; i < 30; i++)
  {
    trellis_buf[(i*8)+0] = (m_data[i] >> 7) & 1;
    trellis_buf[(i*8)+1] = (m_data[i] >> 6) & 1;
    trellis_buf[(i*8)+2] = (m_data[i] >> 5) & 1;
    trellis_buf[(i*8)+3] = (m_data[i] >> 4) & 1;
    trellis_buf[(i*8)+4] = (m_data[i] >> 3) & 1;
    trellis_buf[(i*8)+5] = (m_data[i] >> 2) & 1;
    trellis_buf[(i*8)+6] = (m_data[i] >> 1) & 1;
    trellis_buf[(i*8)+7] = (m_data[i] >> 0) & 1;
  }

  memset (state->m17_lsf, 0, sizeof(state->m17_lsf));
  memcpy (state->m17_lsf, trellis_buf, 240);

  uint8_t lsf_packed[30];
  memset (lsf_packed, 0, sizeof(lsf_packed));

  //need to pack bytes for the sw5wwp variant of the crc (might as well, may be useful in the future)
  for (i = 0; i < 30; i++)
    lsf_packed[i] = (uint8_t)ConvertBitIntoBytes(&state->m17_lsf[i*8], 8);

  uint16_t crc_cmp = crc16m17(lsf_packed, 28);
  uint16_t crc_ext = (uint16_t)ConvertBitIntoBytes(&state->m17_lsf[224], 16);
  int crc_err = 0;

  if (crc_cmp != crc_ext) crc_err = 1;

  if (crc_err == 0)
    M17decodeLSF(state);

  if (opts->payload == 1)
  {
    fprintf (stderr, "\n LSF: ");
    for (i = 0; i < 30; i++)
    {
      if (i == 15) fprintf (stderr, "\n      ");
      fprintf (stderr, "[%02X]", lsf_packed[i]);
    }
  }

  //debug
  // fprintf (stderr, " E-%04X; C-%04X (CRC CHK)", crc_ext, crc_cmp);

  if (crc_err == 1) fprintf (stderr, " CRC ERR");

  //ending linebreak
  fprintf (stderr, "\n");

} //end processM17LSF