According to Which pins can be used as external interrupts on the SAMD21? - TechOverflow the samd21 controller should be able to handle external interrupts on all digital pins on the Nano 33 Iot, as the product specification on the store pages confirms.
But as noted in earlier posts, not all (digital) pins generate interrupts.
Can this be an error in the c library of the samd arduino products? I think the hardware should be capable to handle the interrupts.
I would like to use D4 to generate interrupts.
riendenboer:
Can this be an error in the c library of the samd arduino products? I think the hardware should be capable to handle the interrupts.
This is not necessarily an error. If you look at the variant.cpp file, the pin has a setting EXTERNAL_INT_NONE which somewhere probably configure the interrupt settings. So, this has been set deliberately. There might be side effects that would affect other things in Arduino sketches. Arduino set these settings so they would work for many different applications. But, for some it might not.
You can find the file in the following folder.
C:\Users\UserName\AppData\Local\Arduino15\packages\arduino\hardware\samd\1.8.6\variants\nano_33_iot
riendenboer:
I would like to use D4 to generate interrupts.
You need to figure out how to modify the files for your use case. Maybe you can simply steal the EXTERNAL_INT_ from another pin.