Reading from AS3955

[benkli]

Please answer these questions as part of your new issue.

Which version of Python are you using?

2.7.9

Which OS and version are you running?

Linux raspberrypi 4.4.38-v7+

Is SPI enabled?

yes

Are you trying to read/write a Mifare Classic card? (This is currently unsupported)

I'm trying to read an AMS AS3955 NFC interface tag. This tag acts as an NFC type 2 tag (mifare ultralight)

Hey there! I'm trying to read data from an AMS AS3955 NFC interface tag. When reading and writing from EEPROM data section 0 -> 127 everthing works fine. But when I'm trying to read from the AS3955 extendend memory section (0xfc -> 0xff), I'm getting:

nxppy.ReadError: Nxppy: Protocol Error, response violated protocol from Mifare PAL-Component

According to the AS3955 datasheet, I can access this area via normal read and write commands. Writing to this section works, I can read the written data with the MCU attached to the AS3955. But I can not read the data from this section with nxppy. I've run out of ideas. Thank you in advance for your help!

Yours, Benjamin

[benkli]

Strange! When reading from memory 0xfc alone, an error does not occure. But the returned data is always 0.

Edit 1:

PyObject *Mifare_read_block(Mifare * self, PyObject * args)
{
    uint8_t blockIdx;
    uint8_t bDataBuffer[READ_BUFFER_LEN];

    if (!PyArg_ParseTuple(args, "b", &blockIdx)) {
        return NULL;
    }

    phStatus_t status = 0;

    status = phalMful_Read(&(self->nfcData.salMfc), blockIdx, bDataBuffer);
    if (handle_error(status, ReadError)) return NULL;

    // The read command reads a full 16 bytes, but we only want to return 1 page worth of data for this command.
#if PY_MAJOR_VERSION >= 3
    return Py_BuildValue("y#", bDataBuffer, MFC_BLOCK_DATA_SIZE);
#else
    return Py_BuildValue("s#", bDataBuffer, MFC_BLOCK_DATA_SIZE);
#endif
}

Could changing "MFC_BLOCK_DATA_SIZE" to 16 in this area, solve the problem?

Edit 2:

Ok. I've found the problem for me. I have to change the "MFC_BLOCK_DATA_SIZE" to 16, for reading from this extended data area. Sorry for causing any inconveniences.

Yours Benjamin.

[svvitale]

Was the MFC_BLOCK_DATA_SIZE the only change you made? Any other side effects that you can tell? If not, I'd like to merge your changes into master. Mind filing a pull request?

[benkli]

Hi Scott! I copied the mifare_read(...) function and made a second one named mifare_read16(...). This one had the changed MFC_BLOCK_DATA_SIZE=16 in it. This solution enabled me to interface the AS3955’s buffer. I Couldn’t recognize any side effects.

[svvitale]

Ah, no problem. I'll give it a try using your description and we can go from there. I'll ping you again when I need a guinea pig :). I'll reopen this issue since it is something that needs to be fixed.