Determine the end of an NFC Write?

[CurtisHx]

Is there a way to determine the end of an NFC write besides waiting for the NFC_T4T_EVENT_FIELD_OFF event? We want to update the NDEF message from within firmware after data is written but before the NFC_T4T_EVENT_FIELD_OFF event fires. We tried doing the update on NFC_T4T_EVENT_NDEF_UPDATED when data_length is greater than 0 in nfc_callback, but that doesn't work.

UpdateNdefMessage reads the ndef message that was just written to the device, and then updates the ndef message based on what was written.

Is there a way to determine when a write is finished without relying on NFC_T4T_EVENT_FIELD_OFF?

	static void nfc_callback(
  void          * context     __attribute__((unused)),
	nfc_t4t_event_t event       __attribute__((unused)),
	const uint8_t * data        __attribute__((unused)),
	size_t          dataLength  __attribute__((unused)),
	uint32_t        flags       __attribute__((unused)))
{
	switch (event)
	{
	case NFC_T4T_EVENT_NDEF_READ:
		break;
	case NFC_T4T_EVENT_NDEF_UPDATED:
		if (dataLength > 0)
		{
			UpdateNdefMessage();
		}
		break;
	default:
		break;
	}
}

[CurtisHx]

It's consistent across phones. The NFC Tools doesn't read back the newly written content because the UpdateNdefMessage function writes over the NDEF buffer within the NFC Type 4 library.

[CurtisHx]

We came up with a work-around. We configured a hardware timer to fire its interrupt a few milliseconds after the last NFC_T4T_EVENT_NDEF_UPDATED event, and do all of the NDEF reconfiguration in there. That solved our problem.

[Michal]

Good that your workaround seems to work.

The only issue I can see with using NFC_T4T_EVENT_NDEF_UPDATED is that UpdateNdefMessage might take long to execute and thus prevent from sending R-APDU (response to UpdateBinary) in time. This is because the callback for NFC_T4T_EVENT_NDEF_UPDATED event is called before sending the proper R-APDU. Other than that, I can't see why updating the NDEF content like you did originally, would not work, maybe some sniffer log could tell us more.