How to address the error: cannot open source input file "core_m3.h": No such file or directory?
Make sure that the correct path to the header. Open the "Options for target", go to the C/C++ tab and make sure that the path to the nrf_drv_gpiote.h is added under "Include paths".
for example, see:
devzone.nordicsemi.com/.../184681
Note that this is standard 'C' (and C++) programming stuff - not specific to Keil, or ARM, or embedded.
Perhaps find the file in your system, probably in a CMSIS directory, and then make sure your project actually lists that directory as part of the "Include Paths" so the tools can find the file.
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