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Add CRC calculation for IL2P #572

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Add CRC calculation for IL2P
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@leventelist
leventelist committed Jun 2, 2025
commit 19596fac12f9a749b6a481665064af38a661970d
1 change: 1 addition & 0 deletions src/audio.h
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Expand Up @@ -208,6 +208,7 @@ struct audio_s {
int il2p_max_fec; // 1 for max FEC length, 0 for automatic based on size.

int il2p_invert_polarity; // 1 means invert on transmit. Receive handles either automatically.
enum il2p_use_crc_t { IL2P_NOCRC = 0, IL2P_USECRC } il2p_use_crc;

enum v26_e { V26_UNSPECIFIED=0, V26_A, V26_B } v26_alternative;

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11 changes: 10 additions & 1 deletion src/config.c
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Expand Up @@ -791,6 +791,7 @@ void config_init (char *fname, struct audio_s *p_audio_config,
p_audio_config->achan[channel].layer2_xmit = LAYER2_AX25;
p_audio_config->achan[channel].il2p_max_fec = 1;
p_audio_config->achan[channel].il2p_invert_polarity = 0;
p_audio_config->achan[channel].il2p_use_crc = IL2P_USECRC;

p_audio_config->achan[channel].fix_bits = DEFAULT_FIX_BITS;
p_audio_config->achan[channel].sanity_test = SANITY_APRS;
Expand Down Expand Up @@ -2625,13 +2626,15 @@ void config_init (char *fname, struct audio_s *p_audio_config,
}

/*
* IL2PTX [ + - ] [ 0 1 ] - Enable IL2P transmission. Default off.
* IL2PTX [ + - ] [ 0 1 ] [ C ] - Enable IL2P transmission. Default off.
* "+" means normal polarity. Redundant since it is the default.
* (command line -I for first channel)
* "-" means inverted polarity. Do not use for 1200 bps.
* (command line -i for first channel)
* "0" means weak FEC. Not recommended.
* "1" means stronger FEC. "Max FEC." Default if not specified.
* "C" means check CRC. Default is not to check CRC.
* Note, that it'll always generate CRC for the frame.
*/

else if (strcasecmp(t, "IL2PTX") == 0) {
Expand All @@ -2644,6 +2647,7 @@ void config_init (char *fname, struct audio_s *p_audio_config,
p_audio_config->achan[channel].layer2_xmit = LAYER2_IL2P;
p_audio_config->achan[channel].il2p_max_fec = 1;
p_audio_config->achan[channel].il2p_invert_polarity = 0;
p_audio_config->achan[channel].il2p_use_crc = IL2P_NOCRC; // Default is no CRC.

while ((t = split(NULL,0)) != NULL) {
for (char *c = t; *c != '\0'; c++) {
Expand All @@ -2659,6 +2663,11 @@ void config_init (char *fname, struct audio_s *p_audio_config,
break;
case '1':
p_audio_config->achan[channel].il2p_max_fec = 1;
break;
case 'C':
case 'c':
p_audio_config->achan[channel].il2p_use_crc = IL2P_USECRC;
dw_printf ("Line %d: IL2P transmission will use CRC.\n", line);
break;
default:
text_color_set(DW_COLOR_ERROR);
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2 changes: 1 addition & 1 deletion src/hdlc_rec.c
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Expand Up @@ -504,7 +504,7 @@ void hdlc_rec_bit_new (int chan, int subchan, int slice, int raw, int is_scrambl

if (g_audio_p->achan[chan].modem_type != MODEM_AIS) {
fx25_rec_bit (chan, subchan, slice, dbit);
il2p_rec_bit (chan, subchan, slice, raw); // Note: skip NRZI.
il2p_rec_bit (chan, subchan, slice, raw, g_audio_p->achan[chan].il2p_use_crc); // Note: skip NRZI.
}

/*
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9 changes: 5 additions & 4 deletions src/il2p.h
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Expand Up @@ -19,6 +19,7 @@

#define IL2P_MAX_PACKET_SIZE (IL2P_SYNC_WORD_SIZE + IL2P_HEADER_SIZE + IL2P_HEADER_PARITY + IL2P_MAX_ENCODED_PAYLOAD_SIZE)

#define IL2P_CODED_CRC_LENGTH 4

///////////////////////////////////////////////////////////////////////////////
//
Expand Down Expand Up @@ -52,7 +53,7 @@ extern void il2p_set_debug(int debug);

// Receives a bit stream from demodulator.

extern void il2p_rec_bit (int chan, int subchan, int slice, int dbit);
extern void il2p_rec_bit (int chan, int subchan, int slice, int dbit, int use_crc);



Expand Down Expand Up @@ -81,9 +82,9 @@ int il2p_send_frame (int chan, packet_t pp, int max_fec, int polarity);

extern int il2p_encode_frame (packet_t pp, int max_fec, unsigned char *iout);

packet_t il2p_decode_frame (unsigned char *irec);
packet_t il2p_decode_frame (unsigned char *irec, int use_crc);

packet_t il2p_decode_header_payload (unsigned char* uhdr, unsigned char *epayload, int *symbols_corrected);
packet_t il2p_decode_header_payload (unsigned char* uhdr, unsigned char *epayload, int *symbols_corrected, int use_crc);



Expand Down Expand Up @@ -138,7 +139,7 @@ extern int il2p_payload_compute (il2p_payload_properties_t *p, int payload_size,

extern int il2p_encode_payload (unsigned char *payload, int payload_size, int max_fec, unsigned char *enc);

extern int il2p_decode_payload (unsigned char *received, int payload_size, int max_fec, unsigned char *payload_out, int *symbols_corrected);
extern int il2p_decode_payload (unsigned char *received, int payload_size, int max_fec, unsigned char *payload_out, int *symbols_corrected, unsigned char **next_hdr);

extern int il2p_get_header_attributes (unsigned char *hdr, int *hdr_type, int *max_fec);

Expand Down
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