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ISO15693 device side improvements (#652)

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* ISO15693 device side improvements
* increase accuracy by doubling the sample frequency (hi_read_rx_xcorr.v)
* adjust armsrc/iso15693.c and client/cmdhf15.c accordingly
* use more accurate approximation for sqrt(ci^2 + cq^2)
* improve EOF detection (was often mistaken for Logic0, resulting in "error, uneven octet! (extra bits!)")
* hi_read_r_xcorr.v: avoid overflows during accumulation and truncation
* explicitely cast unsigned ADC samples to signed
This commit is contained in:
pwpiwi 2018-08-15 14:03:20 +02:00 • committed by GitHub
commit 315e18e66c
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4 changed files with 174 additions and 130 deletions
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120
armsrc/iso15693.c
View file

@ -81,7 +81,10 @@
#define AddCrc(data,datalen) Iso15693AddCrc(data,datalen) #define AddCrc(data,datalen) Iso15693AddCrc(data,datalen)
#define sprintUID(target,uid) Iso15693sprintUID(target,uid) #define sprintUID(target,uid) Iso15693sprintUID(target,uid)
int DEBUG=0; // approximate amplitude=sqrt(ci^2+cq^2)
#define AMPLITUDE(ci, cq) (MAX(ABS(ci), ABS(cq)) + (MIN(ABS(ci), ABS(cq))>>1))
static int DEBUG = 0;
// --------------------------- // ---------------------------
@ -303,13 +306,9 @@ static int GetIso15693AnswerFromTag(uint8_t *receivedResponse, int maxLen, int *
// NOW READ RESPONSE // NOW READ RESPONSE
FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_RX_XCORR); FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_RX_XCORR);
//spindelay(60); // greg - experiment to get rid of some of the 0 byte/failed reads
c = 0; c = 0;
getNext = false; getNext = false;
for(;;) { for(;;) {
if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
AT91C_BASE_SSC->SSC_THR = 0x43;
}
if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) { if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
int8_t b; int8_t b;
b = (int8_t)AT91C_BASE_SSC->SSC_RHR; b = (int8_t)AT91C_BASE_SSC->SSC_RHR;
@ -319,11 +318,11 @@ static int GetIso15693AnswerFromTag(uint8_t *receivedResponse, int maxLen, int *
// every other is Q. We just want power, so abs(I) + abs(Q) is // every other is Q. We just want power, so abs(I) + abs(Q) is
// close to what we want. // close to what we want.
if(getNext) { if(getNext) {
uint8_t r = ABS(b) + ABS(prev); uint8_t r = AMPLITUDE(b, prev);
dest[c++] = (uint8_t)r; dest[c++] = r;
if(c >= 2000) { if(c >= 4000) {
break; break;
} }
} else { } else {
@ -341,12 +340,10 @@ static int GetIso15693AnswerFromTag(uint8_t *receivedResponse, int maxLen, int *
int i, j; int i, j;
int max = 0, maxPos=0; int max = 0, maxPos=0;
int skip = 4; int skip = 2;
// if(GraphTraceLen < 1000) return; // THIS CHECKS FOR A BUFFER TO SMALL
// First, correlate for SOF // First, correlate for SOF
for(i = 0; i < 100; i++) { for(i = 0; i < 200; i++) { // usually, SOF is found around i = 60
int corr = 0; int corr = 0;
for(j = 0; j < arraylen(FrameSOF); j += skip) { for(j = 0; j < arraylen(FrameSOF); j += skip) {
corr += FrameSOF[j]*dest[i+(j/skip)]; corr += FrameSOF[j]*dest[i+(j/skip)];
@ -356,7 +353,7 @@ static int GetIso15693AnswerFromTag(uint8_t *receivedResponse, int maxLen, int *
maxPos = i; maxPos = i;
} }
} }
// Dbprintf("SOF at %d, correlation %d", maxPos,max/(arraylen(FrameSOF)/skip)); if (DEBUG) Dbprintf("SOF at %d, correlation %d", maxPos, max/(arraylen(FrameSOF)/skip));
int k = 0; // this will be our return value int k = 0; // this will be our return value
@ -370,10 +367,15 @@ static int GetIso15693AnswerFromTag(uint8_t *receivedResponse, int maxLen, int *
memset(outBuf, 0, sizeof(outBuf)); memset(outBuf, 0, sizeof(outBuf));
uint8_t mask = 0x01; uint8_t mask = 0x01;
for(;;) { for(;;) {
int corr0 = 0, corr1 = 0, corrEOF = 0; int corr0 = 0, corr00 = 0, corr01 = 0, corr1 = 0, corrEOF = 0;
for(j = 0; j < arraylen(Logic0); j += skip) { for(j = 0; j < arraylen(Logic0); j += skip) {
corr0 += Logic0[j]*dest[i+(j/skip)]; corr0 += Logic0[j]*dest[i+(j/skip)];
} }
corr01 = corr00 = corr0;
for(j = 0; j < arraylen(Logic0); j += skip) {
corr00 += Logic0[j]*dest[i+arraylen(Logic0)/skip+(j/skip)];
corr01 += Logic1[j]*dest[i+arraylen(Logic0)/skip+(j/skip)];
}
for(j = 0; j < arraylen(Logic1); j += skip) { for(j = 0; j < arraylen(Logic1); j += skip) {
corr1 += Logic1[j]*dest[i+(j/skip)]; corr1 += Logic1[j]*dest[i+(j/skip)];
} }
@ -381,11 +383,14 @@ static int GetIso15693AnswerFromTag(uint8_t *receivedResponse, int maxLen, int *
corrEOF += FrameEOF[j]*dest[i+(j/skip)]; corrEOF += FrameEOF[j]*dest[i+(j/skip)];
} }
// Even things out by the length of the target waveform. // Even things out by the length of the target waveform.
corr00 *= 2;
corr01 *= 2;
corr0 *= 4; corr0 *= 4;
corr1 *= 4; corr1 *= 4;
if(corrEOF > corr1 && corrEOF > corr0) { if(corrEOF > corr1 && corrEOF > corr00 && corrEOF > corr01) {
// Dbprintf("EOF at %d", i); if (DEBUG) Dbprintf("EOF at %d, correlation %d (corr01: %d, corr00: %d, corr1: %d, corr0: %d)",
i, corrEOF, corr01, corr00, corr1, corr0);
break; break;
} else if(corr1 > corr0) { } else if(corr1 > corr0) {
i += arraylen(Logic1)/skip; i += arraylen(Logic1)/skip;
@ -398,7 +403,7 @@ static int GetIso15693AnswerFromTag(uint8_t *receivedResponse, int maxLen, int *
k++; k++;
mask = 0x01; mask = 0x01;
} }
if((i+(int)arraylen(FrameEOF)) >= 2000) { if((i+(int)arraylen(FrameEOF)/skip) >= 4000) {
DbpString("ran off end!"); DbpString("ran off end!");
break; break;
} }
@ -446,9 +451,6 @@ static int GetIso15693AnswerFromSniff(uint8_t *receivedResponse, int maxLen, int
c = 0; c = 0;
getNext = false; getNext = false;
for(;;) { for(;;) {
if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
AT91C_BASE_SSC->SSC_THR = 0x43;
}
if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) { if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
int8_t b = (int8_t)AT91C_BASE_SSC->SSC_RHR; int8_t b = (int8_t)AT91C_BASE_SSC->SSC_RHR;
@ -457,11 +459,11 @@ static int GetIso15693AnswerFromSniff(uint8_t *receivedResponse, int maxLen, int
// every other is Q. We just want power, so abs(I) + abs(Q) is // every other is Q. We just want power, so abs(I) + abs(Q) is
// close to what we want. // close to what we want.
if(getNext) { if(getNext) {
uint8_t r = ABS(b) + ABS(prev); uint8_t r = AMPLITUDE(b, prev);
dest[c++] = (uint8_t)r; dest[c++] = r;
if(c >= 20000) { if(c >= BIGBUF_SIZE) {
break; break;
} }
} else { } else {
@ -479,12 +481,10 @@ static int GetIso15693AnswerFromSniff(uint8_t *receivedResponse, int maxLen, int
int i, j; int i, j;
int max = 0, maxPos=0; int max = 0, maxPos=0;
int skip = 4; int skip = 2;
// if(GraphTraceLen < 1000) return; // THIS CHECKS FOR A BUFFER TO SMALL
// First, correlate for SOF // First, correlate for SOF
for(i = 0; i < 19000; i++) { for(i = 0; i < 38000; i++) {
int corr = 0; int corr = 0;
for(j = 0; j < arraylen(FrameSOF); j += skip) { for(j = 0; j < arraylen(FrameSOF); j += skip) {
corr += FrameSOF[j]*dest[i+(j/skip)]; corr += FrameSOF[j]*dest[i+(j/skip)];
@ -494,7 +494,7 @@ static int GetIso15693AnswerFromSniff(uint8_t *receivedResponse, int maxLen, int
maxPos = i; maxPos = i;
} }
} }
// DbpString("SOF at %d, correlation %d", maxPos,max/(arraylen(FrameSOF)/skip)); if (DEBUG) Dbprintf("SOF at %d, correlation %d", maxPos,max/(arraylen(FrameSOF)/skip));
int k = 0; // this will be our return value int k = 0; // this will be our return value
@ -508,10 +508,15 @@ static int GetIso15693AnswerFromSniff(uint8_t *receivedResponse, int maxLen, int
memset(outBuf, 0, sizeof(outBuf)); memset(outBuf, 0, sizeof(outBuf));
uint8_t mask = 0x01; uint8_t mask = 0x01;
for(;;) { for(;;) {
int corr0 = 0, corr1 = 0, corrEOF = 0; int corr0 = 0, corr00 = 0, corr01 = 0, corr1 = 0, corrEOF = 0;
for(j = 0; j < arraylen(Logic0); j += skip) { for(j = 0; j < arraylen(Logic0); j += skip) {
corr0 += Logic0[j]*dest[i+(j/skip)]; corr0 += Logic0[j]*dest[i+(j/skip)];
} }
corr01 = corr00 = corr0;
for(j = 0; j < arraylen(Logic0); j += skip) {
corr00 += Logic0[j]*dest[i+arraylen(Logic0)/skip+(j/skip)];
corr01 += Logic1[j]*dest[i+arraylen(Logic0)/skip+(j/skip)];
}
for(j = 0; j < arraylen(Logic1); j += skip) { for(j = 0; j < arraylen(Logic1); j += skip) {
corr1 += Logic1[j]*dest[i+(j/skip)]; corr1 += Logic1[j]*dest[i+(j/skip)];
} }
@ -519,11 +524,14 @@ static int GetIso15693AnswerFromSniff(uint8_t *receivedResponse, int maxLen, int
corrEOF += FrameEOF[j]*dest[i+(j/skip)]; corrEOF += FrameEOF[j]*dest[i+(j/skip)];
} }
// Even things out by the length of the target waveform. // Even things out by the length of the target waveform.
corr00 *= 2;
corr01 *= 2;
corr0 *= 4; corr0 *= 4;
corr1 *= 4; corr1 *= 4;
if(corrEOF > corr1 && corrEOF > corr0) { if(corrEOF > corr1 && corrEOF > corr00 && corrEOF > corr01) {
// DbpString("EOF at %d", i); if (DEBUG) Dbprintf("EOF at %d, correlation %d (corr01: %d, corr00: %d, corr1: %d, corr0: %d)",
i, corrEOF, corr01, corr00, corr1, corr0);
break; break;
} else if(corr1 > corr0) { } else if(corr1 > corr0) {
i += arraylen(Logic1)/skip; i += arraylen(Logic1)/skip;
@ -536,7 +544,7 @@ static int GetIso15693AnswerFromSniff(uint8_t *receivedResponse, int maxLen, int
k++; k++;
mask = 0x01; mask = 0x01;
} }
if((i+(int)arraylen(FrameEOF)) >= 2000) { if((i+(int)arraylen(FrameEOF)/skip) >= BIGBUF_SIZE) {
DbpString("ran off end!"); DbpString("ran off end!");
break; break;
} }
@ -602,10 +610,6 @@ void AcquireRawAdcSamplesIso15693(void)
break; break;
} }
} }
if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
volatile uint32_t r = AT91C_BASE_SSC->SSC_RHR;
(void)r;
}
WDT_HIT(); WDT_HIT();
} }
@ -614,9 +618,6 @@ void AcquireRawAdcSamplesIso15693(void)
c = 0; c = 0;
getNext = false; getNext = false;
for(;;) { for(;;) {
if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
AT91C_BASE_SSC->SSC_THR = 0x43;
}
if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) { if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
int8_t b; int8_t b;
b = (int8_t)AT91C_BASE_SSC->SSC_RHR; b = (int8_t)AT91C_BASE_SSC->SSC_RHR;
@ -626,11 +627,11 @@ void AcquireRawAdcSamplesIso15693(void)
// every other is Q. We just want power, so abs(I) + abs(Q) is // every other is Q. We just want power, so abs(I) + abs(Q) is
// close to what we want. // close to what we want.
if(getNext) { if(getNext) {
uint8_t r = ABS(b) + ABS(prev); uint8_t r = AMPLITUDE(b, prev);
dest[c++] = (uint8_t)r; dest[c++] = r;
if(c >= 2000) { if(c >= 4000) {
break; break;
} }
} else { } else {
@ -668,9 +669,6 @@ void RecordRawAdcSamplesIso15693(void)
c = 0; c = 0;
getNext = false; getNext = false;
for(;;) { for(;;) {
if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
AT91C_BASE_SSC->SSC_THR = 0x43;
}
if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) { if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
int8_t b; int8_t b;
b = (int8_t)AT91C_BASE_SSC->SSC_RHR; b = (int8_t)AT91C_BASE_SSC->SSC_RHR;
@ -680,11 +678,11 @@ void RecordRawAdcSamplesIso15693(void)
// every other is Q. We just want power, so abs(I) + abs(Q) is // every other is Q. We just want power, so abs(I) + abs(Q) is
// close to what we want. // close to what we want.
if(getNext) { if(getNext) {
uint8_t r = ABS(b) + ABS(prev); uint8_t r = AMPLITUDE(b, prev);
dest[c++] = (uint8_t)r; dest[c++] = r;
if(c >= 7000) { if(c >= 14000) {
break; break;
} }
} else { } else {
@ -836,7 +834,7 @@ int SendDataTag(uint8_t *send, int sendlen, int init, int speed, uint8_t **recv)
if (init) Iso15693InitReader(); if (init) Iso15693InitReader();
int answerLen=0; int answerLen=0;
uint8_t *answer = BigBuf_get_addr() + 3660; uint8_t *answer = BigBuf_get_addr() + 4000;
if (recv != NULL) memset(answer, 0, 100); if (recv != NULL) memset(answer, 0, 100);
if (!speed) { if (!speed) {
@ -957,7 +955,7 @@ void ReaderIso15693(uint32_t parameter)
int answerLen1 = 0; int answerLen1 = 0;
int answerLen2 = 0; int answerLen2 = 0;
int answerLen3 = 0; // int answerLen3 = 0;
int i = 0; int i = 0;
int samples = 0; int samples = 0;
int tsamples = 0; int tsamples = 0;
@ -967,11 +965,11 @@ void ReaderIso15693(uint32_t parameter)
FpgaDownloadAndGo(FPGA_BITSTREAM_HF); FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
uint8_t *answer1 = BigBuf_get_addr() + 3660; uint8_t *answer1 = BigBuf_get_addr() + 4000;
uint8_t *answer2 = BigBuf_get_addr() + 3760; uint8_t *answer2 = BigBuf_get_addr() + 4100;
uint8_t *answer3 = BigBuf_get_addr() + 3860; // uint8_t *answer3 = BigBuf_get_addr() + 4200;
// Blank arrays // Blank arrays
memset(answer1, 0x00, 300); memset(answer1, 0x00, 200);
SetAdcMuxFor(GPIO_MUXSEL_HIPKD); SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
// Setup SSC // Setup SSC
@ -1025,13 +1023,13 @@ void ReaderIso15693(uint32_t parameter)
TagUID[3],TagUID[2],TagUID[1],TagUID[0]); TagUID[3],TagUID[2],TagUID[1],TagUID[0]);
Dbprintf("%d octets read from SELECT request:", answerLen2); // Dbprintf("%d octets read from SELECT request:", answerLen2);
DbdecodeIso15693Answer(answerLen2,answer2); // DbdecodeIso15693Answer(answerLen2,answer2);
Dbhexdump(answerLen2,answer2,true); // Dbhexdump(answerLen2,answer2,true);
Dbprintf("%d octets read from XXX request:", answerLen3); // Dbprintf("%d octets read from XXX request:", answerLen3);
DbdecodeIso15693Answer(answerLen3,answer3); // DbdecodeIso15693Answer(answerLen3,answer3);
Dbhexdump(answerLen3,answer3,true); // Dbhexdump(answerLen3,answer3,true);
// read all pages // read all pages
if (answerLen1>=12 && DEBUG) { if (answerLen1>=12 && DEBUG) {
@ -1073,7 +1071,7 @@ void SimTagIso15693(uint32_t parameter, uint8_t *uid)
FpgaDownloadAndGo(FPGA_BITSTREAM_HF); FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
uint8_t *buf = BigBuf_get_addr() + 3660; uint8_t *buf = BigBuf_get_addr() + 4000;
memset(buf, 0x00, 100); memset(buf, 0x00, 100);
SetAdcMuxFor(GPIO_MUXSEL_HIPKD); SetAdcMuxFor(GPIO_MUXSEL_HIPKD);

31
client/cmdhf15.c
View file

@ -268,7 +268,7 @@ static char* TagErrorStr(uint8_t error) {
case 0x02: return "The command is not recognised"; case 0x02: return "The command is not recognised";
case 0x03: return "The option is not supported."; case 0x03: return "The option is not supported.";
case 0x0f: return "Unknown error."; case 0x0f: return "Unknown error.";
case 0x10: return "The specified block is not available (doesn’t exist)."; case 0x10: return "The specified block is not available (doesn't exist).";
case 0x11: return "The specified block is already -locked and thus cannot be locked again"; case 0x11: return "The specified block is already -locked and thus cannot be locked again";
case 0x12: return "The specified block is locked and its content cannot be changed."; case 0x12: return "The specified block is locked and its content cannot be changed.";
case 0x13: return "The specified block was not successfully programmed."; case 0x13: return "The specified block was not successfully programmed.";
@ -286,12 +286,12 @@ int CmdHF15Demod(const char *Cmd)
int i, j; int i, j;
int max = 0, maxPos = 0; int max = 0, maxPos = 0;
int skip = 4; int skip = 2;
if (GraphTraceLen < 1000) return 0; if (GraphTraceLen < 2000) return 0;
// First, correlate for SOF // First, correlate for SOF
for (i = 0; i < 100; i++) { for (i = 0; i < 200; i++) {
int corr = 0; int corr = 0;
for (j = 0; j < arraylen(FrameSOF); j += skip) { for (j = 0; j < arraylen(FrameSOF); j += skip) {
corr += FrameSOF[j] * GraphBuffer[i + (j / skip)]; corr += FrameSOF[j] * GraphBuffer[i + (j / skip)];
@ -310,21 +310,28 @@ int CmdHF15Demod(const char *Cmd)
memset(outBuf, 0, sizeof(outBuf)); memset(outBuf, 0, sizeof(outBuf));
uint8_t mask = 0x01; uint8_t mask = 0x01;
for (;;) { for (;;) {
int corr0 = 0, corr1 = 0, corrEOF = 0; int corr0 = 0, corr00 = 0, corr01 = 0, corr1 = 0, corrEOF = 0;
for (j = 0; j < arraylen(Logic0); j += skip) { for(j = 0; j < arraylen(Logic0); j += skip) {
corr0 += Logic0[j] * GraphBuffer[i + (j / skip)]; corr0 += Logic0[j]*GraphBuffer[i+(j/skip)];
} }
for (j = 0; j < arraylen(Logic1); j += skip) { corr01 = corr00 = corr0;
corr1 += Logic1[j] * GraphBuffer[i + (j / skip)]; for(j = 0; j < arraylen(Logic0); j += skip) {
corr00 += Logic0[j]*GraphBuffer[i+arraylen(Logic0)/skip+(j/skip)];
corr01 += Logic1[j]*GraphBuffer[i+arraylen(Logic0)/skip+(j/skip)];
} }
for (j = 0; j < arraylen(FrameEOF); j += skip) { for(j = 0; j < arraylen(Logic1); j += skip) {
corrEOF += FrameEOF[j] * GraphBuffer[i + (j / skip)]; corr1 += Logic1[j]*GraphBuffer[i+(j/skip)];
}
for(j = 0; j < arraylen(FrameEOF); j += skip) {
corrEOF += FrameEOF[j]*GraphBuffer[i+(j/skip)];
} }
// Even things out by the length of the target waveform. // Even things out by the length of the target waveform.
corr00 *= 2;
corr01 *= 2;
corr0 *= 4; corr0 *= 4;
corr1 *= 4; corr1 *= 4;
if (corrEOF > corr1 && corrEOF > corr0) { if(corrEOF > corr1 && corrEOF > corr00 && corrEOF > corr01) {
PrintAndLog("EOF at %d", i); PrintAndLog("EOF at %d", i);
break; break;
} else if (corr1 > corr0) { } else if (corr1 > corr0) {

BIN
fpga/fpga_hf.bit
View file

Binary file not shown.

119
fpga/hi_read_rx_xcorr.v
View file

@ -27,21 +27,11 @@ assign pwr_hi = ck_1356megb & (~snoop);
assign pwr_oe1 = 1'b0; assign pwr_oe1 = 1'b0;
assign pwr_oe3 = 1'b0; assign pwr_oe3 = 1'b0;
assign pwr_oe4 = 1'b0; assign pwr_oe4 = 1'b0;
// Unused.
assign pwr_lo = 1'b0;
assign pwr_oe2 = 1'b0;
reg [2:0] fc_div; assign adc_clk = ck_1356megb; // sample frequency is 13,56 MHz
always @(negedge ck_1356megb)
fc_div <= fc_div + 1;
(* clock_signal = "yes" *) reg adc_clk; // sample frequency, always 16 * fc
always @(ck_1356megb, xcorr_is_848, xcorr_quarter_freq, fc_div)
if (xcorr_is_848 & ~xcorr_quarter_freq) // fc = 847.5 kHz, standard ISO14443B
adc_clk <= ck_1356megb;
else if (~xcorr_is_848 & ~xcorr_quarter_freq) // fc = 423.75 kHz
adc_clk <= fc_div[0];
else if (xcorr_is_848 & xcorr_quarter_freq) // fc = 211.875 kHz
adc_clk <= fc_div[1];
else // fc = 105.9375 kHz
adc_clk <= fc_div[2];
// When we're a reader, we just need to do the BPSK demod; but when we're an // When we're a reader, we just need to do the BPSK demod; but when we're an
// eavesdropper, we also need to pick out the commands sent by the reader, // eavesdropper, we also need to pick out the commands sent by the reader,
@ -69,15 +59,27 @@ begin
end end
end end
// Let us report a correlation every 4 subcarrier cycles, or 4*16=64 samples,
// so we need a 6-bit counter. // Let us report a correlation every 64 samples. I.e.
// one Q/I pair after 4 subcarrier cycles for the 848kHz subcarrier,
// one Q/I pair after 2 subcarrier cycles for the 424kHz subcarriers,
// one Q/I pair for each subcarrier cyle for the 212kHz subcarrier.
// We need a 6-bit counter for the timing.
reg [5:0] corr_i_cnt; reg [5:0] corr_i_cnt;
// And a couple of registers in which to accumulate the correlations. always @(negedge adc_clk)
// We would add at most 32 times the difference between unmodulated and modulated signal. It should begin
corr_i_cnt <= corr_i_cnt + 1;
end
// And a couple of registers in which to accumulate the correlations. From the 64 samples
// we would add at most 32 times the difference between unmodulated and modulated signal. It should
// be safe to assume that a tag will not be able to modulate the carrier signal by more than 25%. // be safe to assume that a tag will not be able to modulate the carrier signal by more than 25%.
// 32 * 255 * 0,25 = 2040, which can be held in 11 bits. Add 1 bit for sign. // 32 * 255 * 0,25 = 2040, which can be held in 11 bits. Add 1 bit for sign.
reg signed [11:0] corr_i_accum; // Temporary we might need more bits. For the 212kHz subcarrier we could possible add 32 times the
reg signed [11:0] corr_q_accum; // maximum signal value before a first subtraction would occur. 32 * 255 = 8160 can be held in 13 bits.
// Add one bit for sign -> need 14 bit registers but final result will fit into 12 bits.
reg signed [13:0] corr_i_accum;
reg signed [13:0] corr_q_accum;
// we will report maximum 8 significant bits // we will report maximum 8 significant bits
reg signed [7:0] corr_i_out; reg signed [7:0] corr_i_out;
reg signed [7:0] corr_q_out; reg signed [7:0] corr_q_out;
@ -86,11 +88,28 @@ reg ssp_clk;
reg ssp_frame; reg ssp_frame;
always @(negedge adc_clk) // The subcarrier reference signals
begin reg subcarrier_I;
corr_i_cnt <= corr_i_cnt + 1; reg subcarrier_Q;
end
always @(corr_i_cnt or xcorr_is_848 or xcorr_quarter_freq)
begin
if (xcorr_is_848 & ~xcorr_quarter_freq) // 848 kHz
begin
subcarrier_I = ~corr_i_cnt[3];
subcarrier_Q = ~(corr_i_cnt[3] ^ corr_i_cnt[2]);
end
else if (xcorr_is_848 & xcorr_quarter_freq) // 212 kHz
begin
subcarrier_I = ~corr_i_cnt[5];
subcarrier_Q = ~(corr_i_cnt[5] ^ corr_i_cnt[4]);
end
else
begin // 424 kHz
subcarrier_I = ~corr_i_cnt[4];
subcarrier_Q = ~(corr_i_cnt[4] ^ corr_i_cnt[3]);
end
end
// ADC data appears on the rising edge, so sample it on the falling edge // ADC data appears on the rising edge, so sample it on the falling edge
always @(negedge adc_clk) always @(negedge adc_clk)
@ -103,36 +122,60 @@ begin
if(snoop) if(snoop)
begin begin
// Send 7 most significant bits of tag signal (signed), plus 1 bit reader signal // Send 7 most significant bits of tag signal (signed), plus 1 bit reader signal
if (corr_i_accum[13:11] == 3'b000 || corr_i_accum[13:11] == 3'b111)
corr_i_out <= {corr_i_accum[11:5], after_hysteresis_prev_prev}; corr_i_out <= {corr_i_accum[11:5], after_hysteresis_prev_prev};
else // truncate to maximum value
if (corr_i_accum[13] == 1'b0)
corr_i_out <= {7'b0111111, after_hysteresis_prev_prev};
else
corr_i_out <= {7'b1000000, after_hysteresis_prev_prev};
if (corr_q_accum[13:11] == 3'b000 || corr_q_accum[13:11] == 3'b111)
corr_q_out <= {corr_q_accum[11:5], after_hysteresis_prev}; corr_q_out <= {corr_q_accum[11:5], after_hysteresis_prev};
else // truncate to maximum value
if (corr_q_accum[13] == 1'b0)
corr_q_out <= {7'b0111111, after_hysteresis_prev};
else
corr_q_out <= {7'b1000000, after_hysteresis_prev};
after_hysteresis_prev_prev <= after_hysteresis; after_hysteresis_prev_prev <= after_hysteresis;
end end
else else
begin begin
// 8 bits of tag signal // Send 8 bits of tag signal
if (corr_i_accum[13:11] == 3'b000 || corr_i_accum[13:11] == 3'b111)
corr_i_out <= corr_i_accum[11:4]; corr_i_out <= corr_i_accum[11:4];
else // truncate to maximum value
if (corr_i_accum[13] == 1'b0)
corr_i_out <= 8'b01111111;
else
corr_i_out <= 8'b10000000;
if (corr_q_accum[13:11] == 3'b000 || corr_q_accum[13:11] == 3'b111)
corr_q_out <= corr_q_accum[11:4]; corr_q_out <= corr_q_accum[11:4];
else // truncate to maximum value
if (corr_q_accum[13] == 1'b0)
corr_q_out <= 8'b01111111;
else
corr_q_out <= 8'b10000000;
end end
// Initialize next correlation.
corr_i_accum <= adc_d; // Both I and Q reference signals are high when corr_i_nct == 0. Therefore need to accumulate.
corr_q_accum <= adc_d; corr_i_accum <= $signed({1'b0,adc_d});
corr_q_accum <= $signed({1'b0,adc_d});
end end
else else
begin begin
if(corr_i_cnt[3]) if (subcarrier_I)
corr_i_accum <= corr_i_accum - adc_d; corr_i_accum <= corr_i_accum + $signed({1'b0,adc_d});
else else
corr_i_accum <= corr_i_accum + adc_d; corr_i_accum <= corr_i_accum - $signed({1'b0,adc_d});
if(corr_i_cnt[3] == corr_i_cnt[2]) // phase shifted by pi/2 if (subcarrier_Q)
corr_q_accum <= corr_q_accum + adc_d; corr_q_accum <= corr_q_accum + $signed({1'b0,adc_d});
else else
corr_q_accum <= corr_q_accum - adc_d; corr_q_accum <= corr_q_accum - $signed({1'b0,adc_d});
end end
// The logic in hi_simulate.v reports 4 samples per bit. We report two // for each Q/I pair report two reader signal samples when sniffing
// (I, Q) pairs per bit, so we should do 2 samples per pair.
if(corr_i_cnt == 6'd32) if(corr_i_cnt == 6'd32)
after_hysteresis_prev <= after_hysteresis; after_hysteresis_prev <= after_hysteresis;
@ -167,8 +210,4 @@ assign ssp_din = corr_i_out[7];
assign dbg = corr_i_cnt[3]; assign dbg = corr_i_cnt[3];
// Unused.
assign pwr_lo = 1'b0;
assign pwr_oe2 = 1'b0;
endmodule endmodule