- int i, j, clock, header, rows, bit, hithigh, hitlow, first, bit2idx, high, low;
- int parity[4];
- char id[11];
- int retested = 0;
- uint8_t BitStream[MAX_GRAPH_TRACE_LEN];
- high = low = 0;
-
- /* Detect high and lows and clock */
- for (i = 0; i < GraphTraceLen; i++)
- {
- if (GraphBuffer[i] > high)
- high = GraphBuffer[i];
- else if (GraphBuffer[i] < low)
- low = GraphBuffer[i];
- }
-
- /* get clock */
- clock = GetClock(Cmd, high, 0);
-
- /* parity for our 4 columns */
- parity[0] = parity[1] = parity[2] = parity[3] = 0;
- header = rows = 0;
-
- /* manchester demodulate */
- bit = bit2idx = 0;
- for (i = 0; i < (int)(GraphTraceLen / clock); i++)
- {
- hithigh = 0;
- hitlow = 0;
- first = 1;
-
- /* Find out if we hit both high and low peaks */
- for (j = 0; j < clock; j++)
- {
- if (GraphBuffer[(i * clock) + j] == high)
- hithigh = 1;
- else if (GraphBuffer[(i * clock) + j] == low)
- hitlow = 1;
-
- /* it doesn't count if it's the first part of our read
- because it's really just trailing from the last sequence */
- if (first && (hithigh || hitlow))
- hithigh = hitlow = 0;
- else
- first = 0;
-
- if (hithigh && hitlow)
- break;
- }
-
- /* If we didn't hit both high and low peaks, we had a bit transition */
- if (!hithigh || !hitlow)
- bit ^= 1;
-
- BitStream[bit2idx++] = bit;
- }
-
-retest:
- /* We go till 5 before the graph ends because we'll get that far below */
- for (i = 1; i < bit2idx - 5; i++)
- {
- /* Step 2: We have our header but need our tag ID */
- if (header == 9 && rows < 10)
- {
- /* Confirm parity is correct */
- if ((BitStream[i] ^ BitStream[i+1] ^ BitStream[i+2] ^ BitStream[i+3]) == BitStream[i+4])
- {
- /* Read another byte! */
- sprintf(id+rows, "%x", (8 * BitStream[i]) + (4 * BitStream[i+1]) + (2 * BitStream[i+2]) + (1 * BitStream[i+3]));
- rows++;
-
- /* Keep parity info */
- parity[0] ^= BitStream[i];
- parity[1] ^= BitStream[i+1];
- parity[2] ^= BitStream[i+2];
- parity[3] ^= BitStream[i+3];
-
- /* Move 4 bits ahead */
- i += 4;
- }
-
- /* Damn, something wrong! reset */
- else
- {
- PrintAndLog("Thought we had a valid tag but failed at word %d (i=%d)", rows + 1, i);
-
- /* Start back rows * 5 + 9 header bits, -1 to not start at same place */
- i -= 9 + (5 * rows) - 5;
-
- rows = header = 0;
- }
- }
-
- /* Step 3: Got our 40 bits! confirm column parity */
- else if (rows == 10)
- {
- /* We need to make sure our 4 bits of parity are correct and we have a stop bit */
- if (BitStream[i] == parity[0] && BitStream[i+1] == parity[1] &&
- BitStream[i+2] == parity[2] && BitStream[i+3] == parity[3] &&
- BitStream[i+4] == 0)
- {
- /* Sweet! */
- PrintAndLog("EM410x Tag ID: %s", id);
-
- /* Stop any loops */
- return 1;
- }
-
- /* Crap! Incorrect parity or no stop bit, start all over */
- else
- {
- rows = header = 0;
-
- /* Go back 59 bits (9 header bits + 10 rows at 4+1 parity) */
- i -= 59;
- }
- }
-
- /* Step 1: get our header */
- else if (header < 9)
- {
- /* Need 9 consecutive 1's */
- if (BitStream[i] == 1)
- header++;
-
- /* We don't have a header, not enough consecutive 1 bits */
- else
- header = 0;
- }
- }
-
- /* if we've already retested after flipping bits, return */
- if (retested++)