IBM PowerPC 405GP User Manual page 240

7. Software resets the UICO_ER field for the low priority interrupt, disabling it; UICO_ VR contains
OxOOOOOOOO.
8. UICO_CR is reprogrammed to make the low priority interrupt non-critical and UICO_ER is
reprogrammed to re-enable the low priority interrupt; UICO_ VR continues to contain OxOOOOOOOO.
Preliminary Interrupt Controller Operations
10-21