Incorrect mapping of analog pins to ADC channels for ATmega1284/P, ATmega644/A/P/PA

[JChristensen]

For the ATmega1284/P and 644/A/P/PA MCUs, analogRead() uses a hardcoded algorithm that causes it to incorrectly map analog pin numbers to ADC channels for certain popular boards including some of those defined in maniacbug's mighty-1284p core.

Calling analogPinToChannel(), similar to what is already in place for the ATtinyX5 MCUs, would address this issue and allow better flexibility for future boards that may be developed.

Pull request to follow.

[Lauszus]

This was implemented almost a year ago: #1368.

[JChristensen]

Yes, I see that now, I was mis-reading the code. Sorry for the inconvenience. Closing the issue.