PPT Slide
Interrupt Structure (continued)
- CRA-1 Interrupt Handling - when one of the four types of interrupts occurs the following steps are taken (ref. Table 2.2 for interrupt vector table):
- ipsw <- psw (save current program state)
- psw <- 0 (set to system mode; disable future interrupts)
- ip <- interrupt parameter (if appropriate, e.g. - program error)
- iia <- ia (save current execution address)
- ia <- (interruptNumber * 4) + iva (control passes to the appropriate interrupt routine via the interrupt vector table)
- After the interrupt handler routine is done, it issues the rti instruction, which returns control & state to the point of execution prior to the interrupt
- ia <- iia
- psw <- ipws
- Restore any regs that may have been used