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em4x70: clean up check_ack function

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This commit is contained in:
Christian Molson 2020-12-14 00:38:41 -05:00
parent a2c21f1d07
commit afbef5ba73
1 changed files with 10 additions and 23 deletions
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33
armsrc/em4x70.c
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@ -287,30 +287,17 @@ static void em4x70_send_word(const uint16_t word) {
}
static bool check_ack(void) {
// returns true if signal structue corresponds to ACK, anything else is
// counted as NAK (-> false)
uint32_t start_ticks = GetTicks();
while (TICKS_ELAPSED(start_ticks) < (4 * EM4X70_T_TAG_FULL_PERIOD)) {
/*
ACK
64 (48+16)
64 (48+16)
NACK
64 (48+16)
48 (32+16)
*/
if (check_pulse_length(get_pulse_length(FALLING_EDGE), 2 * EM4X70_T_TAG_FULL_PERIOD)) {
// The received signal is either ACK or NAK.
if (check_pulse_length(get_pulse_length(FALLING_EDGE), 2 * EM4X70_T_TAG_FULL_PERIOD)) {
return true;
} else {
// It's NAK -> stop searching
break;
}
}
}
// ACK 64 + 64
// NACK 64 + 48
if (check_pulse_length(get_pulse_length(FALLING_EDGE), 2 * EM4X70_T_TAG_FULL_PERIOD) &&
check_pulse_length(get_pulse_length(FALLING_EDGE), 2 * EM4X70_T_TAG_FULL_PERIOD)) {
// ACK
return true;
}
// Othewise it was a NACK or Listen Window
return false;
}
@ -415,7 +402,7 @@ static int write(const uint16_t word, const uint8_t address) {
// look for ACK sequence
if (check_ack()) {
// now EM4x70 needs T0 * EM4X70_T_TAG_TWEE (EEPROM write time)
// now EM4x70 needs EM4X70_T_TAG_TWEE (EEPROM write time)
// for saving data and should return with ACK
WaitTicks(EM4X70_T_TAG_WEE);
if (check_ack()) {