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Increase CRC size to 32-bits. This breaks backwards compatibility.

This commit is contained in:
Philip Heron 2012-09-16 12:32:53 +01:00
parent d3bc9dca2d
commit 662629e501
2 changed files with 27 additions and 19 deletions
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43
ssdv.c
View File

@ -153,21 +153,24 @@ static void *dtblcpy(ssdv_t *s, const void *src, size_t n)
return(r);
}
#ifndef crc_xmodem_update
uint16_t crc_xmodem_update(uint16_t crc, uint8_t data)
static uint32_t crc32(void *data, size_t length)
{
int i;
uint32_t crc, x;
uint8_t i, *d;
crc = crc ^ ((uint16_t) data << 8);
for(i = 0; i < 8; i++)
for(d = data, crc = 0xFFFFFFFF; length; length--)
{
if(crc & 0x8000) crc = (crc << 1) ^ 0x1021;
else crc <<= 1;
x = (crc ^ *(d++)) & 0xFF;
for(i = 8; i > 0; i--)
{
if(x & 1) x = (x >> 1) ^ 0xEDB88320;
else x >>= 1;
}
crc = (crc >> 8) ^ x;
}
return(crc);
return(crc ^ 0xFFFFFFFF);
}
#endif
static uint32_t encode_callsign(char *callsign)
{
@ -920,8 +923,8 @@ char ssdv_enc_get_packet(ssdv_t *s)
if(r == SSDV_BUFFER_FULL || r == SSDV_EOI)
{
uint16_t mcu_id = s->packet_mcu_id;
uint8_t mcu_offset = s->packet_mcu_offset;
uint16_t i, x;
uint8_t i, mcu_offset = s->packet_mcu_offset;
uint32_t x;
if(mcu_offset != 0xFF && mcu_offset >= SSDV_PKT_SIZE_PAYLOAD)
{
@ -958,10 +961,12 @@ char ssdv_enc_get_packet(ssdv_t *s)
if(s->out_len > 0) ssdv_memset_prng(s->outp, s->out_len);
/* Calculate the CRC codes */
for(i = 1, x = 0xFFFF; i < SSDV_PKT_SIZE - SSDV_PKT_SIZE_RSCODES - SSDV_PKT_SIZE_CRC; i++)
x = crc_xmodem_update(x, s->out[i]);
x = crc32(&s->out[1], SSDV_PKT_SIZE_CRCDATA);
s->out[i++] = x >> 8;
i = 1 + SSDV_PKT_SIZE_CRCDATA;
s->out[i++] = (x >> 24) & 0xFF;
s->out[i++] = (x >> 16) & 0xFF;
s->out[i++] = (x >> 8) & 0xFF;
s->out[i++] = x & 0xFF;
/* Generate the RS codes */
@ -1259,7 +1264,7 @@ char ssdv_dec_is_packet(uint8_t *packet, int *errors)
{
uint8_t pkt[SSDV_PKT_SIZE];
ssdv_packet_info_t p;
uint16_t x;
uint32_t x;
int i;
/* Testing is destructive, work on a copy */
@ -1284,10 +1289,12 @@ char ssdv_dec_is_packet(uint8_t *packet, int *errors)
}
/* Test the checksum */
for(i = 1, x = 0xFFFF; i < SSDV_PKT_SIZE - SSDV_PKT_SIZE_RSCODES - SSDV_PKT_SIZE_CRC; i++)
x = crc_xmodem_update(x, pkt[i]);
x = crc32(&pkt[1], SSDV_PKT_SIZE_CRCDATA);
if(pkt[i++] != (x >> 8)) return(-1);
i = 1 + SSDV_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 */

3
ssdv.h
View File

@ -34,9 +34,10 @@ extern "C" {
/* Packet details */
#define SSDV_PKT_SIZE (0x100)
#define SSDV_PKT_SIZE_HEADER (0x0F)
#define SSDV_PKT_SIZE_CRC (0x02)
#define SSDV_PKT_SIZE_CRC (0x04)
#define SSDV_PKT_SIZE_RSCODES (0x20)
#define SSDV_PKT_SIZE_PAYLOAD (SSDV_PKT_SIZE - SSDV_PKT_SIZE_HEADER - SSDV_PKT_SIZE_CRC - SSDV_PKT_SIZE_RSCODES)
#define SSDV_PKT_SIZE_CRCDATA (SSDV_PKT_SIZE_HEADER + SSDV_PKT_SIZE_PAYLOAD - 1)
#define TBL_LEN (546) /* Maximum size of the DQT and DHT tables */
#define HBUFF_LEN (16) /* Extra space for reading marker data */