18. Cache Test Mode
A.7 Instruction Fetch, Decode, Issue, Execution, Completion, and Graduation
In general, instructions are fetched, decoded, and graduated in their original program order, but may be issued, executed, and completed out of program order, as shown in Figure A-1.
- Instruction fetching is the process of reading instructions from the instruction cache.
- Instruction decode includes register renaming and initial dependency checks. For branch instructions, the branch path is predicted and the target address is computed.
- An instruction is issued when it is handed over to a functional unit for execution.
- An instruction is complete when its result has been computed and stored in a temporary physical register.
- An instruction graduates when this temporary result is committed as the new state of the processor. An instruction can graduate only after it and all previous instructions have been successfully completed.
Figure A-1 Dynamic Scheduling
Copyright 1996, 1997, MIPS Technologies, Inc. -- 09 DEC 96
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