NFC hiding events?

RE: NFC hiding events?

Lee Daniel Crocker — Fri, 16 Feb 2018 18:00:22 GMT

Sounds like it may have something to do with how I'm writing, then. On the other side, I'm sending ISO-7816 messages directly, and I'm only sending a single update (0xD6) command, overwriting the old text with one of the same length. I have since changed my firmware to look for the actual changed data so I don't need the callback anymore. If I have some time, I'll trim my firmware down to something uploadable and let you take a look.

RE: NFC hiding events?

Mttrinh — Fri, 16 Feb 2018 15:58:28 GMT

Hi,

The NFC_T4T_EVENT_NDEF_READ is only reported once during one “session” i.e. between NFC_T4T_EVENT_FIELD_ON and NFC_T4T_EVENT_FIELD_OFF events. So if the tag was read, then written (data on the tag was updated), another read will not trigger the READ event, unless FIELD_OFF and/or FIELD_ON event comes. Unfortunately there is no way to change this event’s behavior without modifying the library’s source code. However we plan to release an updated Type 4 Tag library, with a fixed READ event in the next SDK release.

Regarding the NFC_T4T_EVENT_NDEF_UPDATED event, it’s very strange that you don't see these events. They are reported every time the NLEN field (2 most significant bytes of the NDEF file, representing the NDEF message length) is updated. There are typically 2 UPDATE events during a single tag write operation: first the NLEN is set to [0x00, 0x00] to indicate start of the write operation (first UPDATE event), then new data is written, and finally the NLEN is set to the length of the new NDEF message (second UPDATE event). Possible to upload the firmware so we can have a look at it? If this is sensitive code, the case can be turned private.

RE: NFC hiding events?

Lee Daniel Crocker — Tue, 13 Feb 2018 21:29:13 GMT

I tried using raw mode to see what data is being sent/recd, but it makes no sense to me. The first APDU I send is the standard "Application Select", which is 00 A4 04 00 07 D2 76 00 00 85 01 01 00. The DATA_IND events I get show E0 50 (twice), then E0, then 50 00, then a huge 509-byte monster of some kind, none of which resemble what I sent.