+
+//search for given preamble in given BitStream and return success=1 or fail=0 and startIndex
+uint8_t EMpreambleSearch(uint8_t *BitStream, uint8_t *preamble, size_t pLen, size_t size, size_t *startIdx)
+{
+ // Sanity check. If preamble length is bigger than bitstream length.
+ if ( size <= pLen ) return 0;
+ // em only sends preamble once, so look for it once in the first x bits
+ uint8_t foundCnt = 0;
+ for (int idx = 0; idx < size - pLen; idx++){
+ if (memcmp(BitStream+idx, preamble, pLen) == 0){
+ //first index found
+ foundCnt++;
+ if (foundCnt == 1) {
+ *startIdx = idx;
+ return 1;
+ }
+ }
+ }
+ return 0;
+}
+
+int demodEM4x05resp(uint8_t bitsNeeded) {
+ int ans = 0;
+ bool demodFound = false;
+ DemodBufferLen = 0x00;
+ // skip first two 0 bits as they might have been missed in the demod
+ uint8_t preamble[6] = {0,0,1,0,1,0};
+
+ // test for FSK wave (easiest to 99% ID)
+ if (GetFskClock("", FALSE, FALSE)) {
+ //valid fsk clocks found
+ ans = FSKrawDemod("0 0", false);
+ if (!ans) {
+ if (g_debugMode) PrintAndLog("DEBUG: Error - EM4305: FSK Demod failed");
+ //return -1;
+ } else {
+ // set size to 10 to only test first 4 positions for the preamble
+ size_t size = (10 > DemodBufferLen) ? DemodBufferLen : 10;
+ size_t startIdx = 0;
+
+ if (g_debugMode) PrintAndLog("ANS: %d | %u | %u", ans, startIdx, size);
+
+ uint8_t errChk = !EMpreambleSearch(DemodBuffer, preamble, sizeof(preamble), size, &startIdx);
+ if ( errChk == 0) {
+ if (g_debugMode) PrintAndLog("DEBUG: Error - EM4305 preamble not found :: %d", startIdx);
+ //return -1;
+ } else {
+ //can't test size because the preamble doesn't repeat :(
+ //meaning chances of false positives are high.
+ demodFound = true;
+ }
+ }
+ }
+
+ ans = GetPskClock("", FALSE, FALSE);
+ if (ans>0) {
+ PrintAndLog("PSK response possibly found, run `data rawd p1` to attempt to demod");
+ }
+
+ if (!demodFound) {
+ DemodBufferLen = 0x00;
+ //try biphase
+ ans = ASKbiphaseDemod("0 0 1", FALSE);
+ if (!ans) {
+ if (g_debugMode) PrintAndLog("DEBUG: Error - EM4305: ASK/biphase Demod failed");
+ //return -1;
+ } else {
+ // set size to 10 to only test first 4 positions for the preamble
+ size_t size = (10 > DemodBufferLen) ? DemodBufferLen : 10;
+ size_t startIdx = 0;
+
+ if (g_debugMode) PrintAndLog("ANS: %d | %u | %u", ans, startIdx, size);
+
+ uint8_t errChk = !EMpreambleSearch(DemodBuffer, preamble, sizeof(preamble), size, &startIdx);
+ if ( errChk == 0) {
+ if (g_debugMode) PrintAndLog("DEBUG: Error - EM4305 preamble not found :: %d", startIdx);
+ //return -1;
+ } else {
+ //can't test size because the preamble doesn't repeat :(
+ //meaning chances of false positives are high.
+ demodFound = true;
+ }
+ }
+ }
+
+ if (!demodFound) {
+ DemodBufferLen = 0x00;
+ // try manchester - NOTE: ST only applies to T55x7 tags.
+ ans = ASKDemod_ext("0,0,1", false, false, 1, false);
+ if (!ans) {
+ if (g_debugMode) PrintAndLog("DEBUG: Error - EM4305: ASK/Manchester Demod failed");
+ //return -1;
+ } else {
+ // set size to 10 to only test first 4 positions for the preamble
+ size_t size = (10 > DemodBufferLen) ? DemodBufferLen : 10;
+ size_t startIdx = 0;
+
+ if (g_debugMode) PrintAndLog("ANS: %d | %u | %u", ans, startIdx, size);
+
+ uint8_t errChk = !EMpreambleSearch(DemodBuffer, preamble, sizeof(preamble), size, &startIdx);
+ if ( errChk == 0) {
+ if (g_debugMode) PrintAndLog("DEBUG: Error - EM4305 preamble not found :: %d", startIdx);
+ //return -1;
+ } else {
+ //can't test size because the preamble doesn't repeat :(
+ //meaning chances of false positives are high.
+ demodFound = true;
+ }
+ }
+ }
+
+ if (demodFound && bitsNeeded < DemodBufferLen) {
+ setDemodBuf(DemodBuffer + ans + sizeof(preamble), bitsNeeded, 0);
+ CmdPrintDemodBuff("x");
+ return 1;
+ }
+ return -1;
+}
+