Type 4 Tag

The Type 4 Tag library implements NFC Type 4 Tag functionality based on the NFC Forum document Type 4 Tag Technical Specification Version 1.0.

Overview 

A Type 4 Tag provides a more sophisticated NFC tag implementation compared to Type 2 Tag. It uses the ISO-DEP (ISO14443-4A) protocol for communication and provides a file system containing Elementary Files (EFs).

For detailed information about the Type 4 Tag protocol, data exchange, and APDU handling, see the Type 4 Tag nrfxlib documentation.

The library supports three different modes of emulation:

Mode	Description
Read-only NDEF	NDEF file cannot be modified. Only field status and read events are signaled.
Read-write NDEF	NDEF file can be modified. Changes to NDEF content are signaled through callback.
Raw ISO-DEP	All APDUs are signaled through the callback. Application handles responses.

Note

Raw ISO-DEP mode is supported by the nrfxlib library but is not implemented in Bare Metal (no sample or application support).

Configuration 

To enable the library, set the CONFIG_NFC_T4T_NRFXLIB Kconfig option.

Usage 

The sequence of initialization functions determines the emulation mode.

NDEF emulation mode 

For read-only or read-write NDEF tag emulation:

Register callback and initialize.

Implement a callback function to handle NFC events and register it using the nfc_t4t_setup() function:

static void nfc_callback(void *context,
                         nfc_t4t_event_t event,
                         const uint8_t *data,
                         size_t data_length,
                         uint32_t flags)
{
    switch (event) {
    case NFC_T4T_EVENT_FIELD_ON:
        /* NFC field detected */
        break;
    case NFC_T4T_EVENT_FIELD_OFF:
        /* NFC field removed */
        break;
    case NFC_T4T_EVENT_NDEF_READ:
        /* NDEF data has been read */
        break;
    case NFC_T4T_EVENT_NDEF_UPDATED:
        /* NDEF content was updated (read-write mode) */
        break;
    default:
        break;
    }
}

int err = nfc_t4t_setup(nfc_callback, NULL);
if (err != 0) {
    /* Handle error */
}

Set NDEF payload.

First encode the NDEF file (see NDEF file) for use as the tag payload. Then pass the resulting buffer to one of the following:

For read-only mode, use the nfc_t4t_ndef_staticpayload_set() function:

static const uint8_t ndef_msg[] = { /* NDEF message data */ };

err = nfc_t4t_ndef_staticpayload_set(ndef_msg, sizeof(ndef_msg));
if (err != 0) {
    /* Handle error */
}

For read-write mode, use the nfc_t4t_ndef_rwpayload_set() function:

static uint8_t ndef_buffer[1024];

/* Initialize ndef_buffer with initial NDEF message */
err = nfc_t4t_ndef_rwpayload_set(ndef_buffer, sizeof(ndef_buffer));
if (err != 0) {
    /* Handle error */
}

Start emulation.

err = nfc_t4t_emulation_start();
if (err != 0) {
    /* Handle error */
}

Events 

The library signals the following events through the registered callback:

Event	Description
`NFC_T4T_EVENT_FIELD_ON`	External reader polling detected
`NFC_T4T_EVENT_FIELD_OFF`	External reader polling ended
`NFC_T4T_EVENT_NDEF_READ`	Reader has read static NDEF data (read-only mode)
`NFC_T4T_EVENT_NDEF_UPDATED`	Reader has written to NDEF data (read-write mode)
`NFC_T4T_EVENT_DATA_TRANSMITTED`	Response PDU sent in raw mode
`NFC_T4T_EVENT_DATA_IND`	APDU fragment received in raw mode

Parameters 

You can configure the following parameters using the nfc_t4t_parameter_set() function:

NFC_T4T_PARAM_FWI - Frame Wait Time parameter. Maximum allowed value is limited by the NFC_T4T_PARAM_FWI_MAX parameter.
NFC_T4T_PARAM_FDT_MIN - Frame Delay Time Min parameter for collision resolution timing.
NFC_T4T_PARAM_SELRES - Protocol bits for SEL_RES packet.
NFC_T4T_PARAM_NFCID1 - NFCID1 value. Data can be 4, 7, or 10 bytes long.
NFC_T4T_PARAM_FWI_MAX - Maximum value for Frame Wait Time Integer (7 for EMV, 8 for NFC specification).

Dependencies 

This library requires the following drivers and libraries:

NFCT driver from nrfx
NFC Platform module
NDEF encoding (for example, NDEF messages and NDEF file)

The NFC: Text record for Type 4 Tag sample demonstrates how to use this library.

API reference 

Header file: nrfxlib/nfc/include/nfc_t4t_lib.h

Library: nrfxlib/nfc/lib/

Type 4 Tag library API reference