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AMPS: Add option to be more tollerant to sync detection

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Also it detects more false syncs, but this is ignored if decoding fails.
This commit is contained in:
Andreas Eversberg
2016-10-29 09:15:00 +02:00
parent 42ddd3320e
commit bb92a1f3b0
5 changed files with 41 additions and 10 deletions
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30
src/amps/dsp.c
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@@ -125,6 +125,8 @@ static double sat_freq[5] = {
static int dsp_sine_sat[256];
static uint8_t dsp_sync_check[0x800];
/* global init for FSK */
void dsp_init(void)
{
@@ -136,6 +138,17 @@ void dsp_init(void)
s = sin((double)i / 256.0 * 2.0 * PI);
dsp_sine_sat[i] = (int)(s * SAT_DEVIATION);
}
/* sync checker */
for (i = 0; i < 0x800; i++) {
dsp_sync_check[i] = 0xff; /* no sync */
}
for (i = 0; i < 11; i++) {
dsp_sync_check[0x712 ^ (1 << i)] = 0x01; /* one bit error */
dsp_sync_check[0x0ed ^ (1 << i)] = 0x81; /* one bit error */
}
dsp_sync_check[0x712] = 0x00; /* no bit error */
dsp_sync_check[0x0ed] = 0x80; /* no bit error */
}
static void dsp_init_ramp(amps_t *amps)
@@ -160,7 +173,7 @@ static void dsp_init_ramp(amps_t *amps)
static void sat_reset(amps_t *amps, const char *reason);
/* Init FSK of transceiver */
int dsp_init_sender(amps_t *amps, int high_pass)
int dsp_init_sender(amps_t *amps, int high_pass, int tolerant)
{
double coeff;
int16_t *spl;
@@ -240,6 +253,9 @@ int dsp_init_sender(amps_t *amps, int high_pass)
amps->highpass_factor = RC / (RC + dt);
}
/* be more tolerant when syncing */
amps->fsk_rx_sync_tolerant = tolerant;
return 0;
error:
@@ -508,7 +524,11 @@ static void fsk_rx_bit(amps_t *amps, int16_t *spl, int len, int pos, int begin,
if (amps->fsk_rx_sync != FSK_SYNC_POSITIVE && amps->fsk_rx_sync != FSK_SYNC_NEGATIVE) {
amps->fsk_rx_sync_register = (amps->fsk_rx_sync_register << 1) | bit;
/* check if we received a sync */
if ((amps->fsk_rx_sync_register & 0x7ff) == 0x712) {
switch (dsp_sync_check[amps->fsk_rx_sync_register & 0x7ff]) {
case 0x01:
if (!amps->fsk_rx_sync_tolerant)
break;
case 0x00:
#ifdef DEBUG_DECODER
printf("Sync word detected (positive)\n");
#endif
@@ -520,8 +540,10 @@ prepare_frame:
amps->fsk_rx_sync_register = 0x555;
amps->when_received = get_time() - (21.0 / (double)BITRATE);
return;
}
if ((amps->fsk_rx_sync_register & 0x7ff) == 0x0ed) {
case 0x81:
if (!amps->fsk_rx_sync_tolerant)
break;
case 0x80:
#ifdef DEBUG_DECODER
printf("Sync word detected (negative)\n");
#endif