The default handlers are pretty useless, and mostly just spin wait.
These are defined in the device startup script (for mbed):
https://github.com/lancaster-university/mbed-classic/blob/genuino/targets/cmsis/TARGET_Atmel/TARGET_SAM_CortexM0P/TARGET_SAMD21/TARGET_GENUINO_G18A/TOOLCHAIN_GCC_ARM/startup_samd21.c#L142
Should be pretty trivial to override as they are weak symbols.
The default handlers are pretty useless, and mostly just spin wait.
These are defined in the device startup script (for mbed):
https://github.com/lancaster-university/mbed-classic/blob/genuino/targets/cmsis/TARGET_Atmel/TARGET_SAM_CortexM0P/TARGET_SAMD21/TARGET_GENUINO_G18A/TOOLCHAIN_GCC_ARM/startup_samd21.c#L142
Should be pretty trivial to override as they are weak symbols.