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Bypass the FEC if the packet has a valid CRC

This commit is contained in:
Philip Heron 2016-04-04 00:28:25 +01:00
parent fc3f3f2dff
commit e6a3cfbe42
2 changed files with 56 additions and 17 deletions
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68
ssdv.c
View File

@ -1300,19 +1300,50 @@ char ssdv_dec_is_packet(uint8_t *packet, int *errors)
memcpy(pkt, packet, SSDV_PKT_SIZE);
pkt[0] = 0x55;
type = SSDV_TYPE_INVALID;
if(pkt[1] == 0x66 + SSDV_TYPE_NOFEC)
{
type = SSDV_TYPE_NOFEC;
/* Test for a valid NOFEC packet */
pkt_size_payload = SSDV_PKT_SIZE - SSDV_PKT_SIZE_HEADER - SSDV_PKT_SIZE_CRC;
pkt_size_crcdata = SSDV_PKT_SIZE_HEADER + pkt_size_payload - 1;
/* No FEC scan */
if(errors) *errors = 0;
}
else
{
type = SSDV_TYPE_NORMAL;
/* Test the checksum */
x = crc32(&pkt[1], pkt_size_crcdata);
i = 1 + pkt_size_crcdata;
if(x == (pkt[i + 3] | (pkt[i + 2] << 8) | (pkt[i + 1] << 16) | (pkt[i] << 24)))
{
/* Valid, set the type and continue */
type = SSDV_TYPE_NOFEC;
}
}
else if(pkt[1] == 0x66 + SSDV_TYPE_NORMAL)
{
/* Test for a valid NORMAL packet */
pkt_size_payload = SSDV_PKT_SIZE - SSDV_PKT_SIZE_HEADER - SSDV_PKT_SIZE_CRC - SSDV_PKT_SIZE_RSCODES;
pkt_size_crcdata = SSDV_PKT_SIZE_HEADER + pkt_size_payload - 1;
/* No FEC scan */
if(errors) *errors = 0;
/* Test the checksum */
x = crc32(&pkt[1], pkt_size_crcdata);
i = 1 + pkt_size_crcdata;
if(x == (pkt[i + 3] | (pkt[i + 2] << 8) | (pkt[i + 1] << 16) | (pkt[i] << 24)))
{
/* Valid, set the type and continue */
type = SSDV_TYPE_NORMAL;
}
}
if(type == SSDV_TYPE_INVALID)
{
/* Test for a valid NORMAL packet with correctable errors */
pkt_size_payload = SSDV_PKT_SIZE - SSDV_PKT_SIZE_HEADER - SSDV_PKT_SIZE_CRC - SSDV_PKT_SIZE_RSCODES;
pkt_size_crcdata = SSDV_PKT_SIZE_HEADER + pkt_size_payload - 1;
@ -1322,6 +1353,22 @@ char ssdv_dec_is_packet(uint8_t *packet, int *errors)
if(i < 0) return(-1); /* Reed-solomon decoder failed */
if(errors) *errors = i;
/* Test the checksum */
x = crc32(&pkt[1], pkt_size_crcdata);
i = 1 + pkt_size_crcdata;
if(x == (pkt[i + 3] | (pkt[i + 2] << 8) | (pkt[i + 1] << 16) | (pkt[i] << 24)))
{
/* Valid, set the type and continue */
type = SSDV_TYPE_NORMAL;
}
}
if(type == SSDV_TYPE_INVALID)
{
/* All attempts to read the packet have failed */
return(-1);
}
/* Sanity checks */
@ -1335,15 +1382,6 @@ char ssdv_dec_is_packet(uint8_t *packet, int *errors)
if(p.mcu_offset >= pkt_size_payload) return(-1);
}
/* Test the checksum */
x = crc32(&pkt[1], pkt_size_crcdata);
i = 1 + pkt_size_crcdata;
if(pkt[i++] != ((x >> 24) & 0xFF)) return(-1);
if(pkt[i++] != ((x >> 16) & 0xFF)) return(-1);
if(pkt[i++] != ((x >> 8) & 0xFF)) return(-1);
if(pkt[i++] != (x & 0xFF)) return(-1);
/* Appears to be a valid packet! Copy it back */
memcpy(packet, pkt, SSDV_PKT_SIZE);

5
ssdv.h
View File

@ -42,8 +42,9 @@ extern "C" {
#define SSDV_MAX_CALLSIGN (6) /* Maximum number of characters in a callsign */
#define SSDV_TYPE_NORMAL (0)
#define SSDV_TYPE_NOFEC (1)
#define SSDV_TYPE_INVALID (0xFF)
#define SSDV_TYPE_NORMAL (0x00)
#define SSDV_TYPE_NOFEC (0x01)
typedef struct
{