`-mmcu=` not passed while generating dependencies

[matthijskooijman]

I haven't thoroughly verified this, but arduino/Arduino#4512 (comment) seems to indicate that, while running the preprocessor to collect dependencies, the -mmcu= option is not passed to gcc. You would say that this is not needed for preprocessing, but this also prevents defines like __AVR_ATmega328p__ from being present, which could be used to determine what libraries to use (as happens in this library).

[matthijskooijman]

@cmaglie, I think this is something to fix for the next release.

[cmaglie]

There is a smaller sketch that we can use to reproduce the problem? (sorry I didn't read the full thread yet...)

[matthijskooijman]

I had a closer look, and it seems the problem is that digistup does not define the recipe.preproc.macros value. arduino-builder has a default value for it, but that does not seem to include -mmcu (at least not when combined with the digistump platform.txt.

Looking through the history, the arduino-builder version never had the -mmcu option, and the Arduino version always had it, so I'm not sure what happened there.

I was going to suggest to remove the recipe.preproc.macros entry from Arduino's platform.txt and use the below sketch, but that doesn't seem to break it somehow (-mmcu is still passed). Not sure if that's a problem on my setup (possibly it's using a different platform.txt than I think it is), but no more time to test now. So, here's the sketch:

#if defined(__AVR__)
#include<Wire.h>
#endif

void setup() {
    Wire.begin();
}

void loop() {
}

[per1234]

I think that test sketch doesn't cause the issue because __AVR__ is defined by -DARDUINO_ARCH_{build.arch} which is in the arduino-builder default recipe.preproc.macros. edit: I'm wrong on this, that's not what defines __AVR__

• Comment recipe.preproc.macros in the Arduino AVR Boards platform.txt.
• Tools > Board > Arduino/Genuino Uno
• Compile:

#ifndef __AVR_ATmega328P__
#error
#endif
void setup() {}
void loop() {}

Arduino IDE 1.6.8 2016/02/24 06:33:

sketch_feb28a:2: error: #error 

 #error

  ^

exit status 1
#error 

Note that the arduino-builder default recipe.preproc.includes is also missing -mmcu={build.mcu} which is in Arduino AVR Boards 1.6.9 platform.txt but I haven't found a case where that causes a problem.