Communication problems with NTAG213

We've played with it and were able to get around it by modifying nfc/dev/pn53x.py

The problem was caused by the fact, that for the mentioned commands nfcpy uses
self.chipset.in_data_exchange method, while it should use self.chipset.in_communicate_through

This changed the cmd_code from 0x40 to 0x42 while sending commands line PWD_AUTH or READ_SIG, which fixed the problem.

For now we're selecting the right method basing on the cmd_data value, for the command marked with [2] here: https://www.dropbox.com/s/vsbc0twg10mlz13/Screenshot%202014-10-21%2016.57.46.png?dl=0 (screen from NTAG213 documentation by NXP).

Many thanks for spotting this problem with pn53x based readers. I'll work out an update to use in_communicate_thru for tag reading.

Hello Tomasz,

I think I have the same issue trying to read the signature of NXP NTAG212!
https://answers.launchpad.net/nfcpy/+question/248114

Is it possible to have the updated code of nfc/dev/pn53x.py ?

Thanks again

Hi there,

I've ended up with a quick fix in the command methind inside nfc/dev/acr122.py (I use the ACR122U reader).
Here's the changed definition of this function:

    def command(self, cmd_code, cmd_data=None, timeout=100):
        """Send a chip command and return the chip response."""
        cmd_name = "PN53x "+self.CMD.get(cmd_code, "0x{0:02X}".format(cmd_code))
        log.debug("{0} called with timeout {1} ms".format(cmd_name, timeout))

        if cmd_data is None: cmd_data = ""
 if len(cmd_data) > 1 and bytearray(cmd_data)[1] in [0x1B, 0x3C, 0x60, 0x39]:
   cmd_code = 0x42
   cmd_data = cmd_data[1:]
        frame = bytearray([0xD4, cmd_code]) + bytearray(cmd_data)
 # Temporary fix, nfcpy problem described here: https://answers.launchpad.net/nfcpy/+question/255995
 # Manually overriding cmd_code value to 0x42
 ### end fix
        frame = bytearray([0xFF, 0x00, 0x00, 0x00, len(frame)]) + frame

        frame = self.ccid_xfr_block(frame, timeout)
        if not frame or len(frame) < 4:
            log.error("insufficient data for decoding chip response")
            raise IOError(errno.EIO, os.strerror(errno.EIO))
        if not (frame[0] == 0xD5 and frame[1] == cmd_code + 1):
            log.error("received invalid chip response")
            raise IOError(errno.EIO, os.strerror(errno.EIO))
        if not (frame[-2] == 0x90 and frame[-1] == 0x00):
            log.error("received pseudo apdu with error status")
            raise IOError(errno.EIO, os.strerror(errno.EIO))
        return frame[2:-2]

I manually change the method code to 0x42 if I detect specific NTAG213 (will also work with NTAG212).
This is definitely not the best way to implement this change, but it was enough in my case.

Thank you Tomasz, this solved my problem

A comprehensive fix is on the way. You can try the development version with "bzr branch lp:~stephen-tiedemann/nfcpy/dev-tags", it'll give you improved handling of type 2 tags, authenticate(...) and protect(...) for Ultralight C and NTAG21x plus the signature bytes accessible with just "sig = tag.signature". The tagtool.py got parameters authenticate and protect with password, see the commit message at http://bazaar.launchpad.net/~stephen-tiedemann/nfcpy/dev-tags/revision/232 for some usage explanantion.

Eventually this will merge into trunk but there's still some other tags to do and to test.