Type2Tag.sector_select makes tag unresponsive

[Stephen Tiedemann]

Originally raised as question https://answers.launchpad.net/nfcpy/+question/285533.

With an NXP NTAG I2C, when selecting sector 3 and then reading into the session register pages yields unrecoverable timeout error. Also just selecting sector 3 and then selecting sector 0 yields unrecoverable timeout error, here in the first half of the sector_select(0) call.

[Stephen Tiedemann (stephen-tiedemann)]

Verified with a just received NTAG I2C 1K demo board.

[Stephen Tiedemann (stephen-tiedemann)]

Identified root cause: the Type2Tag.transceive() method makes two retransmissions when a command times out. This is usually the right thing to do but not in case of the obscure "passive ack", aka just don't answer, invented by a drunk engineer. Will add a retries parameter to transceive() so that it can be configured for this special case.

[James (jamescgmatthews)]

If it helps your development I made the following changes to test the fix:

tty2.py:

Line 532: Added an optional 'tries' parameter to the trasceive argument list:

def transceive(self, data, timeout=0.1, tries=3):

Line 549: Use this parameter for the number of retries:

for retry in range(tries):

Line 518 in the sector_select command set the optional parameter to 1:

self.transceive(chr(sector)+"\0\0\0", timeout=0.001, tries=1)

Some simple code to test reading the NXP 1K with the SCL3711:

        resp = tag.sector_select(3)
        print "Sector select: " + str(resp)

        r1 = tag.read(248)

        self.__logger.info("Read registers: " + binascii.hexlify(r1))

Successfully sets the sector to 3 and reads the session registers

For reference the output is:

Read registers: 7d00f848080121000000000000000000

I can confirm that this agrees with reading the tag using the Android application provide by NXP for this eval board.

[Stephen Tiedemann (stephen-tiedemann)]

Fixed in trunk revision 272
http://bazaar.launchpad.net/~stephen-tiedemann/nfcpy/trunk/revision/272