PPT Slide
- Timer Interrupt Handler
- Handles the timer interrupt, used to protect the CPU.
- Book code is similar to JavaSOS code in SOSTimerIntHandler.java:
- Save current process’ state, if there was one
- Invoke Dispatcher()
- Note CRA-1’s SOS use of special instructions to do a block copy of the registers into a special savearea of kernel memory:
- On CRA-1, we save ia, psw, base & bound, all 32 of the general-purpose registers and set up the system stack (r30)
- The assembly code in the Timer Interrupt Handler is the steps needed for half of a context switch between processes; the Dispatcher() will call RunProcess() to perform the other half.