Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Atmel/AT91SAM9G20/TC0/IMR1#0x0
Interrupt Mask Register (channel = 1)
Counter Overflow
Load Overrun
RA Compare
RB Compare
RC Compare
RA Loading
RB Loading
External Trigger
https://github.com/cmsis-svd/cmsis-svd-data