SPI read_passive_target timeout not working correctly

[BraindeadBZH]

Hi,

When in SPI mode calling read_passive_target with a timeout, a NFC tag is only detect at the very beginning of the poll. This is not the case with i2c which detects tags through all the duration of the timeout.

[tgikal]

The SPI and I2C interfaces use an entirely different backend. The problem looks like it's occurring in adafruit_pn532/spi.py -> _wait_ready.

I believe it's related to the with self._spi as spi: statement calling the class each iteration of the while loop:

def _wait_ready(self, timeout=1):
    """Poll PN532 if status byte is ready, up to `timeout` seconds"""
    status = bytearray([reverse_bit(_SPI_STATREAD), 0])

    timestamp = time.monotonic()
    while (time.monotonic() - timestamp) < timeout:
        with self._spi as spi:
            time.sleep(0.02)   # required
            spi.write_readinto(status, status) #pylint: disable=no-member
        if reverse_bit(status[1]) == 0x01:  # LSB data is read in MSB
            return True      # Not busy anymore!
        else:
            time.sleep(0.01)  # pause a bit till we ask again
    # We timed out!
    return False

Changing the while loop around a bit seems to have corrected it:

def _wait_ready(self, timeout=1):
    """Poll PN532 if status byte is ready, up to `timeout` seconds"""
    status = bytearray([reverse_bit(_SPI_STATREAD), 0])

    timestamp = time.monotonic()
    with self._spi as spi:
        while (time.monotonic() - timestamp) < timeout:
            time.sleep(0.02)   # required
            spi.write_readinto(status, status) #pylint: disable=no-member
            if reverse_bit(status[1]) == 0x01:  # LSB data is read in MSB
                return True      # Not busy anymore!
            else:
                time.sleep(0.1)  # pause a bit till we ask again
    # We timed out!
    return False

[caternuson]

@BraindeadBZH Please try the 2.0.7 version of the library when it becomes available:
https://github.com/adafruit/Adafruit_CircuitPython_PN532/releases/tag/2.0.7

[BraindeadBZH]

Thank you for fixing the issue. Unfortunately I don't have access to the hardware to test this at the moment. I will let you know if I have the chance to get back to this.

[caternuson]

OK. Closing for now. We can reopen if you continue to have the same issue.