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fix hitag demodulation when first positive period is not detected

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This commit is contained in:
Philippe Teuwen 2020-01-15 22:07:49 +01:00
parent b2db893e83
commit da048ea491
1 changed files with 12 additions and 2 deletions
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14
armsrc/hitag2.c
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@ -1436,8 +1436,18 @@ void ReaderHitag(hitag_function htf, hitag_data *htd) {
if (waiting_for_first_edge) { if (waiting_for_first_edge) {
// Just break out of loop after an initial time-out (tag is probably not available) // Just break out of loop after an initial time-out (tag is probably not available)
if (periods == 0) break; if (periods == 0) break;
// Register the number of periods that have passed if (tag_modulation == 0) {
response = t_wait_1 - 64 + periods; // hitag replies always start with 11111 == 1010101010, if we see 0
// it means we missed the first period, e.g. if the signal never crossed 0 since reader signal
// so let's add it:
nrz_samples[nrzs++] = tag_modulation ^ 1;
// Register the number of periods that have passed
// we missed the begin of response but we know it happened one period of 16 earlier
response = t_wait_1 - 64 + periods - 16;
} else {
// Register the number of periods that have passed
response = t_wait_1 - 64 + periods;
}
// Indicate that we have dealt with the first edge // Indicate that we have dealt with the first edge
waiting_for_first_edge = false; waiting_for_first_edge = false;
// The first edge is always a single NRZ bit, force periods on 16 // The first edge is always a single NRZ bit, force periods on 16