PSW.IPL can only be changed in supervisor mode as tasks are always run in user mode. If you implement it as an interrupt handler, it will be in supervisor mode. The interrupt handler can be called using CC-RX's built-in function "int_exception." Interrupt vector numbers 1 to 8 are reserved for RI600V4, so use other numbers.
* In handlers, PSW.IPL should not be lower than when processing starts.