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Fix RFID 125 khz reading #2019

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Fix RFID 125 khz reading #2019

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2ffad45
Fix RFID 125 khz reading
yageek Jan 9, 2026
36f3d3f
Better error handling
yageek Jan 13, 2026
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48 changes: 33 additions & 15 deletions src/modules/rfid/rfid125.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,27 @@
#include "core/sd_functions.h"
#include <globals.h>

#define _HEX_DIGIT_ERROR 0xFF

static uint8_t hex2digit(char ch) {
if (ch >= '0' && ch <= '9') return ch - '0';
if (ch >= 'A' && ch <= 'F') return ch - 'A' + 10;
if (ch >= 'a' && ch <= 'f') return ch - 'a' + 10;
return _HEX_DIGIT_ERROR;
}

static uint8_t hex2int(char *ch) {
uint8_t lnib, rnib, res;
lnib = hex2digit(ch[0]);
if (lnib == _HEX_DIGIT_ERROR) return _HEX_DIGIT_ERROR;

rnib = hex2digit(ch[1]);
if (rnib == _HEX_DIGIT_ERROR) return _HEX_DIGIT_ERROR;

res = ((lnib << 4) | 0x0F) & (rnib | 0xF0);
return res;
}

RFID125::RFID125() {
_initial_state = READ_MODE;
setup();
Expand Down Expand Up @@ -171,8 +192,7 @@ void RFID125::read_card() {

bool RFID125::read_card_data() {
char buff[RFID125_PACKET_SIZE];
uint8_t checksum;
uint32_t tag_id;
uint8_t checksum, check;

if (!_stream) return false;

Expand All @@ -189,21 +209,19 @@ bool RFID125::read_card_data() {

for (int i = 0; i < RFID125_PACKET_SIZE; i++) _tag_data[i] = buff[i];

/* add null and parse checksum */
buff[13] = 0;
checksum = strtol(buff + 11, NULL, 16);
/* add null and parse tag_id */
buff[11] = 0;
tag_id = strtol(buff + 3, NULL, 16);
/* add null and parse version (needs to be xored with checksum) */
buff[3] = 0;
checksum ^= strtol(buff + 1, NULL, 16);
/* We read the provided checksum integer read from UART*/
checksum = hex2int(buff + 11);
if (checksum == _HEX_DIGIT_ERROR) return false;

/* xore the tag_id and validate checksum */
for (uint8_t i = 0; i < 32; i += 8) checksum ^= ((tag_id >> i) & 0xFF);
if (checksum) return false;
/* We compute xor check on payload data */
check = hex2int(&buff[1]);
if (check == _HEX_DIGIT_ERROR) return false;

return true;
for (int i = 3; i < 11; i += 2) {
uint8_t value = hex2int(buff + i);
check ^= value;
}
return check == checksum;
}

void RFID125::clear_stream() {
Expand Down