@kbumsik Could you confirm that you can register and use several EXTI at the same time on your board please ? I suspect a bug in gpio driver for SAML21 and SAMD21 (see #6904 and #6932 )

@dylad That looks pretty important. I will try and post it on #6932 .

@kbumsik Thanks you ! I'm looking forward to your feedback :)

Thanks for this PR, I also would have spent days trying to figure out why the EXTI was not working. Just posted on #6932 that I did not see a problem with two EXTI on my samd21g18a.

@kbumsik can I suggest we add a #else clause with all entries -1 in it? or a #error clause in it? This will give more meaningful results where the CPU_MODEL is not catered for by this block.

@TomKeddie That's what I was thinking at the beginning. But I ended up with this kind of bug is hard to chatch unless the compiler doesn't explicitly warn about this. Since I am a mere user of RIOT I don't know if a scenario that a matched CPU_MODEL is not listed in that block is normal or can be intentional. If this case cannot be intentional I believe we better refuse compiling so that a future developer would notice this when he/she is porting a new SAMD CPU.
I would like to ask about this to the maintainers.

Or, as the middle point, we might do like this using #warning instead:

#else 
    #warning CPU_MODEL is not matched here. This may lead to malfunctioning EXTI.
     {-1,  -1, -1, -1, ... 
     },
     {-1,  -1, -1, -1, ... 
     },
#endif

By the way, -Werror is enabled by default in RIOT. What do you think?

@kbumsik I think that's a great idea, lets push it to the reviewers and see what they think.

and go!