Enable digitalRead on output pins, only enable pull-up in digitalWrite if pin is not output

[sandeepmistry]

Resolves #56 and #94.

• pinMode:
  • enable input mode of output pins, to support using digitalRead to read current value (maintains AVR behaviour).
  • disable pull-up on output mode
• digitalWrite:
  • only enable pull-up if pin is not in output mode and HIGH is passed in, disable pull-up if LOW passed in. (This is similar to [samd] fixing issue #28 #41, but it did not set OUT which is needed to enable pull-up - as per table 22-1 in the SAMD21 datasheet).
  • simplify some duplicated code, by using local variables.

If this is merged #41 can be closed.

[sandeepmistry]

@ArduinoBot build this please

[BlackBrix]

digitalWrite: if the pin is in OUTPUT mode, please do not enable/disable/modify the pull-up at all

will it be this way ?

[sandeepmistry]

@dirk67 yes, this is on of the goals of this pull request, in particular see: https://github.com/sandeepmistry/ArduinoCore-samd/blob/digital-read-write-pullup/cores/arduino/wiring_digital.c#L89-L92

[BlackBrix]

is it within the nightly build already ?

[sandeepmistry]

@ArduinoBot build this please

[ArduinoBot]

✅ Build completed.

⬇️ Build URL: http://downloads.arduino.cc/PR/samd/package_samd-b52_index.json

ℹ️ To test this build:

1. Open the Preferences of the Arduino IDE.
2. Add the Build URL above in the Additional Boards Manager URLs field, and click OK.
3. Open the Boards Manager (menu Tools->Board->Board Manager...)
4. Install Arduino SAMD core - Pull Request Enable digitalRead on output pins, only enable pull-up in digitalWrite if pin is not output #101
5. Select one of the boards under SAMD Pull Request Enable digitalRead on output pins, only enable pull-up in digitalWrite if pin is not output #101 in Tools->Board menu
6. Compile/Upload as usual

[sandeepmistry]

@dirk67 this change has not been merged into master yet, see @ArduinoBot's comment above for instructions on how to try out these changes.

[BlackBrix]

(I am formerly @dirk67)
I tested this and get no errors.
I think this should merged into master now.