PPT Slide
CRA-1 CPU (continued)
- Processor supports dual-mode operation:
- System mode (bit 0 of psw = 0) - all instructions are legal and all addresses are physical (base and bound are not used)
- User mode (bit 0 of psw = 1) - instructions that modify control registers are illegal; all addresses must be less than bound and have base added to them
- Subset of instructions that are important to OS:
- Table 2.1 - note interesting ones:
- loadAll address ; load all 32 regs in one shot
- storeAll address ; store all 32 regs in one shot
- move rM,rN ; move any reg to any other reg
- syscall ; request sys service via S/W interrupt
- rti ; return from interrupt (restore psw, etc.)