Amateurfunk
/
hamnet70
2
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

Add CRC8 to the header 

This should prevent wrong decodings of modcod and packet length, which may disrupt decoding of directly following packets.
This commit is contained in:
Thomas Kolb 2024-01-07 00:02:26 +01:00
parent 16aa2ce92c
commit 07555edfdf
2 changed files with 13 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
impl/src/layer1/packet_mod.c
View File

@ -173,7 +173,7 @@ result_t packet_mod_add_header(packet_mod_ctx_t *ctx)
}
// build the header. All field are transferred in network byte order (big endian).
uint8_t header[4];
uint8_t header[5];
// set length
header[0] = (ctx->raw_data_len >> 8) & 0x07;
@ -183,6 +183,9 @@ result_t packet_mod_add_header(packet_mod_ctx_t *ctx)
header[2] = (ctx->raw_data_crc >> 8) & 0xFF;
header[3] = (ctx->raw_data_crc >> 0) & 0xFF;
// append an 8-bit CRC to the header
crc_append_key(LIQUID_CRC_8, header, 4);
// note: the header is coded and modulated differently than the data.
// encode the header

10
impl/src/layer1/rx.c
View File

@ -15,7 +15,7 @@
#define SYMBOL_BUFFER_SIZE 16384
#define HEADER_SIZE_BYTES 4
#define HEADER_SIZE_BYTES 5 // including CRC
#define FREQ_EST_L 24
#define AGC_BW_ACQUISITION 5e-2f
@ -239,6 +239,14 @@ result_t layer1_rx_process(layer1_rx_t *rx, const float complex *samples, size_t
break;
}
// CRC check
if(crc_check_key(LIQUID_CRC_8, header, HEADER_SIZE_BYTES-1) != LIQUID_OK) {
DEBUG_LOG("Header CRC check failed!\n");
rx->state = RX_STATE_ACQUISITION;
rx->callback(RX_EVT_HEADER_ERROR, NULL, 0);
break;
}
rx->payload_len_bytes = (((uint16_t)header[0] << 8) | header[1]) & 0x07FF;
rx->payload_crc = ((uint16_t)header[2] << 8) | header[3];
rx->modcod = header[0] >> 3;