diff options
Diffstat (limited to 'openpicc')
| -rw-r--r-- | openpicc/application/tc_recv.c | 14 |
1 files changed, 13 insertions, 1 deletions
diff --git a/openpicc/application/tc_recv.c b/openpicc/application/tc_recv.c index fa6b510..b8d7234 100644 --- a/openpicc/application/tc_recv.c +++ b/openpicc/application/tc_recv.c @@ -70,7 +70,19 @@ fiq_buffer_t *tc_sniffer_next_buffer_for_fiq = 0; iso14443_frame rx_frames[TC_RECV_NUMBER_OF_FRAME_BUFFERS]; -#define REAL_FRAME_END 333 +/* The standard defines EOF as a logical 0 followed by 128 carrier cycles without modulation. + * That means that the frame end is either 20+128+128 carrier cycles after the end of the + * last modulation (if there was a 1 bit before the EOF) or 20+64+128 carrier cycles after + * the last modulation. So the correct REAL_FRAME_END setting would be something like + * 276. However, we can detect that the last bit period (that without modulation) is not a + * valid bit much earlier: if the last data bit was 1 there are (ca.) 20 cycles till the start + * of the EOF. Then there are 128 cycles without modulation. The next bit (were it not part of + * the EOF) would have to be either sequence X (for a 1 bit) or sequence Z (for a 0 bit): + * If it were a 0 bit there would be modulation right away, if it were a 1 bit there would be + * modulation after 64 cycles. So the maximum valid time without modulation that is not signalling + * and EOF is 20+128+64. Define REAL_FRAME_END as that value (plus 20 cycles error margin). + */ +#define REAL_FRAME_END (20+128+64+20) static int tc_recv_buffer_overruns = 0; |