riscv-verification/RVVI

ISSUE vs. retire

Closed this issue · 4 comments

Silabs-ArjanB commented

https://github.com/riscv-verification/RVVI/tree/main/RVVI-VLG states:

ISSUE

This is the maximum number of instructions that can be retired during a valid event.

Can the signal be renamed to RETIRE if that is what is means?

eroom1966 commented

The purpose of the ISSUE is to dimension the interface to handle the maximum number of instructions that can be issued concurrently. We would therefore expect the number of instructions to RETIRE concurrently to be between 1 to ISSUE.
We currently have implementations using RVVI where the hart has the ability to issue multiple instructions

Silabs-ArjanB commented

This might cause some confusion on the RTL side. For example the existing CV32E40P can only issue one instruction per cycle but it can retire two instructions per cycle (due to its pipeline architecture).

eroom1966 commented

OK, interesting point- so your suggestion is to dimension this on the maximum number of instructions that can retire concurrently. We had not fully considered the fact that two instructions could retire simultaneously, even though only one could be issued.
You could still define the parameter to be value 2, which would allow you to show 2 instructions retiring simultaneously, but you have a valid point that the name does not quite match the meaning
Thanks for raising this

bit-hack commented

I have renamed the signal to RETIRE as suggested and updated the documentation to reflect this. I'll close this ticket, but please re-open if you think there is still more work to do regarding this.