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rename some constants to increase clarity

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This commit is contained in:
Henry Gabryjelski 2025-03-18 23:06:33 -07:00
commit 8617541660
1 changed files with 9 additions and 7 deletions
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16
armsrc/em4x70.c
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@ -51,7 +51,7 @@ static em4x70_tag_t g_tag = { 0 };
#if 1 // Calculation of ticks for timing functions
// Conversion from Ticks to RF periods
// Nearly every calculation is done in terms of Field Codes (FC) aka RF periods
// 1 us = 1.5 ticks
// 1RF Period = 8us = 12 Ticks
#define TICKS_PER_FC 12
@ -71,10 +71,12 @@ static em4x70_tag_t g_tag = { 0 };
#define EM4X70_T_TAG_TOLERANCE (8 * TICKS_PER_FC) // Tolerance in RF periods for receive/LIW
#define EM4X70_T_TAG_TIMEOUT (4 * EM4X70_T_TAG_FULL_PERIOD) // Timeout if we ever get a pulse longer than this
#define EM4X70_T_WAITING_FOR_LIW 50 // Pulses to wait for listen window
#define EM4X70_T_READ_HEADER_LEN 16 // Read header length (16 bit periods)
#define EM4X70_COMMAND_RETRIES 5 // Attempts to send/read command
#define EM4X70_T_PULSES_TO_SEARCH_FOR_LIW 50 // Pulses to wait for listen window
#define EM4X70_T_PULSES_TO_SEARCH_FOR_HEADER_TRANSITION 16 // Read header length (16 bit periods), wait that many pulses to find transition from the 12x `1` to 4x `0`
#define EM4X70_COMMAND_LIW_SEARCH_RETRIES 5 // Attempts to send/read command
#define EM4X70_MAX_SEND_BITCOUNT 96u // Authentication == CMD(4) + NONCE(56) + DIVERGENCY(7) + FRND(28) == 6 + 56 + 35 == 56 + 41 == 95 bits (NOTE: RM(2) is handled as part of LIW detection)
#define EM4X70_MAX_RECEIVE_BITCOUNT 64u // Maximum bits to receive in response to any command (NOTE: This is EXCLUDING the 16-bit header of 0b1111'1111'1111'0000)
#endif // Calculation of ticks for timing functions
@ -572,7 +574,7 @@ static void bitstream_dump(const em4x70_command_bitstream_t *cmd_bitstream) {
/// @return
static bool send_bitstream_internal(const em4x70_bitstream_t *send) {
// similar to original send_command_and_read, but using provided bitstream
int retries = EM4X70_COMMAND_RETRIES;
int retries = EM4X70_COMMAND_LIW_SEARCH_RETRIES; // only retries finding the LIW ... not the actual command
// TIMING SENSITIVE FUNCTION ... Minimize delays after finding the listen window
while (retries) {
@ -1218,7 +1220,7 @@ static int write(const uint16_t word, const uint8_t address) {
static bool find_listen_window(bool command) {
int cnt = 0;
while (cnt < EM4X70_T_WAITING_FOR_LIW) {
while (cnt < EM4X70_T_PULSES_TO_SEARCH_FOR_LIW) {
/*
80 ( 64 + 16 )
80 ( 64 + 16 )
@ -1361,7 +1363,7 @@ static int em4x70_receive(uint8_t *bits, size_t maximum_bits_to_read) {
WaitTicks(6 * EM4X70_T_TAG_FULL_PERIOD);
// wait until we get the transition from 1's to 0's which is 1.5 full windows
for (int i = 0; i < EM4X70_T_READ_HEADER_LEN; i++) {
for (int i = 0; i < EM4X70_T_PULSES_TO_SEARCH_FOR_HEADER_TRANSITION; i++) {
pl = get_pulse_length(edge);
if (check_pulse_length(pl, 3 * EM4X70_T_TAG_HALF_PERIOD)) {
foundheader = true;