mfrc522 v0.1.0

MFRC522 13.56 MHz RFID reader over SPI.

Application scenarios

• A MIFARE UID reader.
• An access-control prototype.
• A tag-presence detector.

Contract

uint8_t mfrc522_init(mfrc522_t *reader, mfrc522_port_t port);
uint8_t mfrc522_request(mfrc522_t *reader, uint16_t *atqa);
uint8_t mfrc522_anticoll(mfrc522_t *reader, uint8_t uid[5]);
uint8_t mfrc522_read_uid(mfrc522_t *reader, uint8_t uid[4]);

• init performs a soft reset, antenna setup, and version check.
• request sends REQA and returns ATQA.
• anticoll sends the anticollision command and returns UID + BCC.
• read_uid combines both and checks BCC.
• Returns 1 on success, 0 on timeout, collision, or a bus error.

Parameters

• SPI mode 0, up to 10 MHz.
• 3.3 V supply; the antenna pins are not 5 V tolerant.
• A 13.56 MHz card must be within a few centimeters.

Memory and timing

• 4 bytes; one 25-byte command buffer is not required.
• A transceive waits up to 100 ms; the timer is configured for the MFRC522.

Integration

mfrc522_t reader;
uint8_t uid[4];
mfrc522_init(&reader, board_mfrc522_port());
if (mfrc522_read_uid(&reader, uid)) {
    show_uid(uid);
}

Adapters

• The adapter drives NSS, SCK, MOSI, MISO, and the optional reset pin.
• Reference: LibDriver mfrc522 (MIT) and the NXP MFRC522 datasheet.
• This implementation is original and covers UID reading only.

When not to use

• MIFARE Classic block authentication/read/write; extend the command layer.
• A 125 kHz tag; use an EM4100 reader.

Verification

make test covers the init register sequence, REQA, anticollision, BCC

validation, and a missing card.

void *context;
void (*select)(void *context);
uint8_t (*transfer)(void *context, uint8_t value);
void (*deselect)(void *context);
void (*reset)(void *context, uint8_t level);
void (*delay_ms)(void *context, uint16_t milliseconds);

mfrc522_port_t port;