UARTClass.begin -> UARTClass.end -> pinMode fails to change MUX mode back

[celskeggs]

I'm running the UART (Serial1) port for a length of time, then turning it off and trying to use it as an output, but this fails silently. I expect to be able to set the mode to OUTPUT and write values to it after Serial1.end() has been called.

The reason that this fails is that UARTClass::init includes this code:

SET_PIN_MODE(17, UART_MUX_MODE); // Rdx SOC PIN (Arduino header pin 0)
SET_PIN_MODE(16, UART_MUX_MODE); // Txd SOC PIN (Arduino header pin 1)

Notably, this doesn't update ulPinMode in g_APinDescription[0] and g_APinDescription[1].

pinMode() does contain code that is supposed to change the MUX mode back to the correct value:

if (p->ulPinMode != GPIO_MUX_MODE) {
    SET_PIN_MODE(p->ulSocPin, GPIO_MUX_MODE);
    p->ulPinMode = GPIO_MUX_MODE;
}

Unfortunately, this code assumes that ulPinMode is up-to-date. In combination with the missing update in UARTClass::init, this means that pinMode() falsely assumes that it doesn't need to change the MUX mode of the pin.

Expected behavior: pinMode should change the MUX mode of a pin, even if it was previously used by the UART.
Suggested fix, if I understand correctly: Update g_APinDescription[0].ulPinMode and g_APinDescription[1].ulPinMode in UARTClass::init.

[eriknyquist]

Hi @celskeggs, thanks for bringing this to our attention. I'll take a look at this and notify you as soon as it's fixed.