// decode header and re-configure payload decoder
void gmskframesync_decode_header(gmskframesync _q)
{
// pack each 1-bit header symbols into 8-bit bytes
unsigned int num_written;
liquid_pack_bytes(_q->header_mod, GMSKFRAME_H_SYM,
_q->header_enc, GMSKFRAME_H_ENC,
&num_written);
assert(num_written==GMSKFRAME_H_ENC);
// unscramble data
unscramble_data(_q->header_enc, GMSKFRAME_H_ENC);
// run packet decoder
_q->header_valid = packetizer_decode(_q->p_header, _q->header_enc, _q->header_dec);
#if DEBUG_GMSKFRAMESYNC_PRINT
printf("****** header extracted [%s]\n", _q->header_valid ? "valid" : "INVALID!");
#endif
if (!_q->header_valid)
return;
unsigned int n = GMSKFRAME_H_USER;
// first byte is for expansion/version validation
if (_q->header_dec[n+0] != GMSKFRAME_VERSION) {
fprintf(stderr,"warning: gmskframesync_decode_header(), invalid framing version\n");
_q->header_valid = 0;
return;
}
// strip off payload length
unsigned int payload_dec_len = (_q->header_dec[n+1] << 8) | (_q->header_dec[n+2]);
// strip off CRC, forward error-correction schemes
// CRC : most-significant 3 bits of [n+3]
// fec0 : least-significant 5 bits of [n+3]
// fec1 : least-significant 5 bits of [n+4]
unsigned int check = (_q->header_dec[n+3] >> 5 ) & 0x07;
unsigned int fec0 = (_q->header_dec[n+3] ) & 0x1f;
unsigned int fec1 = (_q->header_dec[n+4] ) & 0x1f;
// validate properties
if (check >= LIQUID_CRC_NUM_SCHEMES) {
fprintf(stderr,"warning: gmskframesync_decode_header(), decoded CRC exceeds available\n");
check = LIQUID_CRC_UNKNOWN;
_q->header_valid = 0;
}
if (fec0 >= LIQUID_FEC_NUM_SCHEMES) {
fprintf(stderr,"warning: gmskframesync_decode_header(), decoded FEC (inner) exceeds available\n");
fec0 = LIQUID_FEC_UNKNOWN;
_q->header_valid = 0;
}
if (fec1 >= LIQUID_FEC_NUM_SCHEMES) {
fprintf(stderr,"warning: gmskframesync_decode_header(), decoded FEC (outer) exceeds available\n");
fec1 = LIQUID_FEC_UNKNOWN;
_q->header_valid = 0;
}
// print results
#if DEBUG_GMSKFRAMESYNC_PRINT
printf(" properties:\n");
printf(" * fec (inner) : %s\n", fec_scheme_str[fec0][1]);
printf(" * fec (outer) : %s\n", fec_scheme_str[fec1][1]);
printf(" * CRC scheme : %s\n", crc_scheme_str[check][1]);
printf(" * payload length : %u bytes\n", payload_dec_len);
#endif
// configure payload receiver
if (_q->header_valid) {
// set new packetizer properties
_q->payload_dec_len = payload_dec_len;
_q->check = check;
_q->fec0 = fec0;
_q->fec1 = fec1;
// recreate packetizer object
_q->p_payload = packetizer_recreate(_q->p_payload,
_q->payload_dec_len,
_q->check,
_q->fec0,
_q->fec1);
// re-compute payload encoded message length
_q->payload_enc_len = packetizer_get_enc_msg_len(_q->p_payload);
#if DEBUG_GMSKFRAMESYNC_PRINT
printf(" * payload encoded : %u bytes\n", _q->payload_enc_len);
#endif
// re-allocate buffers accordingly
_q->payload_enc = (unsigned char*) realloc(_q->payload_enc, _q->payload_enc_len*sizeof(unsigned char));
_q->payload_dec = (unsigned char*) realloc(_q->payload_dec, _q->payload_dec_len*sizeof(unsigned char));
}
//
}
// decode header
void flexframesync_decode_header(flexframesync _q)
{
#if DEMOD_HEADER_SOFT
// soft decoding operates on 'header_mod' array directly;
// no need to pack bits
#else
// pack 256 1-bit header symbols into 32 8-bit bytes
unsigned int num_written;
liquid_pack_bytes(_q->header_mod, FLEXFRAME_H_SYM,
_q->header_enc, FLEXFRAME_H_ENC,
&num_written);
assert(num_written==FLEXFRAME_H_ENC);
#endif
#if DEBUG_FLEXFRAMESYNC_PRINT
unsigned int i;
// print header (encoded)
printf("header rx (enc) : ");
for (i=0; i<FLEXFRAME_H_ENC; i++)
printf("%.2X ", _q->header_enc[i]);
printf("\n");
#endif
// unscramble header and run packet decoder
#if DEMOD_HEADER_SOFT
// soft demodulation operates on header_mod directly
unscramble_data_soft(_q->header_mod, FLEXFRAME_H_ENC);
_q->header_valid =
packetizer_decode_soft(_q->p_header, _q->header_mod, _q->header);
#else
unscramble_data(_q->header_enc, FLEXFRAME_H_ENC);
_q->header_valid =
packetizer_decode(_q->p_header, _q->header_enc, _q->header);
#endif
// return if header is invalid
if (!_q->header_valid)
return;
// first several bytes of header are user-defined
unsigned int n = FLEXFRAME_H_USER;
// first byte is for expansion/version validation
if (_q->header[n+0] != FLEXFRAME_VERSION) {
fprintf(stderr,"warning: flexframesync_decode_header(), invalid framing version\n");
_q->header_valid = 0;
return;
}
// strip off payload length
unsigned int payload_dec_len = (_q->header[n+1] << 8) | (_q->header[n+2]);
_q->payload_dec_len = payload_dec_len;
// strip off modulation scheme/depth
unsigned int mod_scheme = _q->header[n+3];
// strip off CRC, forward error-correction schemes
// CRC : most-significant 3 bits of [n+4]
// fec0 : least-significant 5 bits of [n+4]
// fec1 : least-significant 5 bits of [n+5]
unsigned int check = (_q->header[n+4] >> 5 ) & 0x07;
unsigned int fec0 = (_q->header[n+4] ) & 0x1f;
unsigned int fec1 = (_q->header[n+5] ) & 0x1f;
// validate properties
if (mod_scheme == 0 || mod_scheme >= LIQUID_MODEM_NUM_SCHEMES) {
fprintf(stderr,"warning: flexframesync_decode_header(), invalid modulation scheme\n");
_q->header_valid = 0;
return;
}
if (check >= LIQUID_CRC_NUM_SCHEMES) {
fprintf(stderr,"warning: flexframesync_decode_header(), decoded CRC exceeds available\n");
_q->header_valid = 0;
return;
}
if (fec0 >= LIQUID_FEC_NUM_SCHEMES) {
fprintf(stderr,"warning: flexframesync_decode_header(), decoded FEC (inner) exceeds available\n");
_q->header_valid = 0;
return;
}
if (fec1 >= LIQUID_FEC_NUM_SCHEMES) {
fprintf(stderr,"warning: flexframesync_decode_header(), decoded FEC (outer) exceeds available\n");
_q->header_valid = 0;
return;
}
// configure payload receiver
if (_q->header_valid) {
// recreate modem
_q->ms_payload = mod_scheme;
_q->bps_payload = modulation_types[mod_scheme].bps;
_q->demod_payload = modem_recreate(_q->demod_payload, _q->ms_payload);
// set new packetizer properties
_q->check = check;
_q->fec0 = fec0;
_q->fec1 = fec1;
// recreate packetizer object
_q->p_payload = packetizer_recreate(_q->p_payload,
_q->payload_dec_len,
_q->check,
_q->fec0,
_q->fec1);
// re-compute payload encoded message length
_q->payload_enc_len = packetizer_get_enc_msg_len(_q->p_payload);
// re-compute number of modulated payload symbols
div_t d = div(8*_q->payload_enc_len, _q->bps_payload);
_q->payload_mod_len = d.quot + (d.rem ? 1 : 0);
// re-allocate buffers accordingly
// (give encoded a few extra bytes to compensate for repacking)
_q->payload_mod = (unsigned char*) realloc(_q->payload_mod, (_q->payload_mod_len )*sizeof(unsigned char));
_q->payload_enc = (unsigned char*) realloc(_q->payload_enc, (_q->payload_enc_len+8)*sizeof(unsigned char));
_q->payload_dec = (unsigned char*) realloc(_q->payload_dec, (_q->payload_dec_len )*sizeof(unsigned char));
if (_q->payload_mod == NULL || _q->payload_enc == NULL || _q->payload_dec == NULL) {
fprintf(stderr,"error: flexframesync_decode_header(), could not re-allocate payload arrays\n");
_q->header_valid = 0;
return;
}
}
#if DEBUG_FLEXFRAMESYNC_PRINT
// print results
printf("flexframesync_decode_header():\n");
printf(" header crc : %s\n", _q->header_valid ? "pass" : "FAIL");
printf(" check : %s\n", crc_scheme_str[check][1]);
printf(" fec (inner) : %s\n", fec_scheme_str[fec0][1]);
printf(" fec (outer) : %s\n", fec_scheme_str[fec1][1]);
printf(" mod scheme : %s\n", modulation_types[mod_scheme].name);
printf(" payload dec len : %u\n", _q->payload_dec_len);
printf(" payload enc len : %u\n", _q->payload_enc_len);
printf(" payload mod len : %u\n", _q->payload_mod_len);
printf(" user data :");
for (i=0; i<FLEXFRAME_H_USER; i++)
printf(" %.2x", _q->header[i]);
printf("\n");
#endif
}
