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minor fixes for FSK demod

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works better with EM4x03 and t55x7 tags (in theory)...
This commit is contained in:
marshmellow42 2017-02-17 12:59:35 -05:00
commit c85858f524
2 changed files with 34 additions and 10 deletions
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4
armsrc/lfops.c
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@ -1656,10 +1656,10 @@ void EM4xWriteWord(uint32_t flag, uint32_t Data, uint32_t Pwd) {
SendForward(fwd_bit_count);
//Wait for write to complete
//SpinDelay(5);
SpinDelayUs(8000);
//Capture response if one exists
DoAcquisition_default(30, TRUE);
DoAcquisition_default(20, TRUE);
FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF); // field off
LED_A_OFF();

40
common/lfdemod.c
View file

@ -487,19 +487,42 @@ size_t fsk_wave_demod(uint8_t * dest, size_t size, uint8_t fchigh, uint8_t fclow
size_t preLastSample = 0;
size_t LastSample = 0;
size_t currSample = 0;
// sync to first lo-hi transition, and threshold
if ( size < 1024 ) return 0; // not enough samples
// jump to modulating data by finding the first 4 threshold crossings (or first 2 waves)
// in case you have junk or noise at the beginning of the trace...
uint8_t thresholdCnt = 0;
size_t waveSizeCnt = 0;
bool isAboveThreshold = dest[idx] >= threshold_value;
for (; idx < size-20; idx++ ) {
if(dest[idx] < threshold_value && isAboveThreshold) {
thresholdCnt++;
if (thresholdCnt > 4 && waveSizeCnt < fchigh+1) break;
isAboveThreshold = false;
waveSizeCnt = 0;
} else if (dest[idx] >= threshold_value && !isAboveThreshold) {
thresholdCnt++;
if (thresholdCnt > 4 && waveSizeCnt < fchigh+1) break;
isAboveThreshold = true;
waveSizeCnt = 0;
} else {
waveSizeCnt++;
}
if (thresholdCnt > 10) break;
}
if (g_debugMode == 2) prnt("threshold Count reached at %u",idx);
// Need to threshold first sample
// skip 160 samples to allow antenna/samples to settle
if(dest[160] < threshold_value) dest[0] = 0;
if(dest[idx] < threshold_value) dest[0] = 0;
else dest[0] = 1;
idx++;
size_t numBits = 0;
// count cycles between consecutive lo-hi transitions, there should be either 8 (fc/8)
// or 10 (fc/10) cycles but in practice due to noise etc we may end up with anywhere
// between 7 to 11 cycles so fuzz it by treat anything <9 as 8 and anything else as 10
// (could also be fc/5 && fc/7 for fsk1 = 4-9)
for(idx = 161; idx < size-20; idx++) {
for(; idx < size-20; idx++) {
// threshold current value
if (dest[idx] < threshold_value) dest[idx] = 0;
@ -514,13 +537,14 @@ size_t fsk_wave_demod(uint8_t * dest, size_t size, uint8_t fchigh, uint8_t fclow
//do nothing with extra garbage
} else if (currSample < (fchigh-1)) { //6-8 = 8 sample waves (or 3-6 = 5)
//correct previous 9 wave surrounded by 8 waves (or 6 surrounded by 5)
if (LastSample > (fchigh-2) && (preLastSample < (fchigh-1) || preLastSample == 0 )){
if (LastSample > (fchigh-2) && (preLastSample < (fchigh-1))){
dest[numBits-1]=1;
}
dest[numBits++]=1;
} else if (currSample > (fchigh) && !numBits) { //12 + and first bit = unusable garbage
//do nothing with beginning garbage
} else if (currSample > (fchigh+1) && numBits < 3) { //12 + and first two bit = unusable garbage
//do nothing with beginning garbage and reset.. should be rare..
numBits = 0;
} else if (currSample == (fclow+1) && LastSample == (fclow-1)) { // had a 7 then a 9 should be two 8's (or 4 then a 6 should be two 5's)
dest[numBits++]=1;
} else { //9+ = 10 sample waves (or 6+ = 7)