Locate your interrupt jump vector table. I don't know how you have set yours up, however you might want to look into mcu_init.c.. you can see from the jump table, the names of the different interrupt routines and you can set a breakpoint in the routine you are looking for.
An easier way might be to make a file called isr.c and include your interrupt jump table there as well as all the interrupt service routines you want.
Bud
