Due bug: Cannot use pin as digital after analogRead

[trickedj]

Once a pin has been used by analogRead it cannot be returned to digital use with pinMode(xxxx, OUTPUT) because analogRead only frees up the pin when another channel is read. pinMode needs to check if the pin is currently selected for the ADC and if so free it up.

A work around is to free up the pin by selecting a spare with analogRead

I discovered this while porting (from a Uno to Due) a TFT+touchpanel screen which shares digital TFT functions with raw touchpanel resistors.

[agdl]

@trickedj I'll open a pull request for this in order to fix it

[agdl]

here the pull request

#2486

[trickedj]

I am not sure that calling "adc_enable_channel" for the input mode is
correct. Input mode is for digital input and enabling the ADC may cause
a conflict. I think the ADC should only be enabled by AnalogRead.

[agdl]

I wasn't sure too, but i tested it and it works. That if that checks if the channel is changed is a problem.

[facchinm]

I've added some thoughts and code on https://groups.google.com/a/arduino.cc/forum/#!topic/developers/IdhTIT0V5GY ,
I'd be very glad to have some discussion before committing any fix 😉