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Has any one created a verification infrastructure with any of RISC-V implementations? The git repository does have a set of tests and benchmarks but could not find any thing more than that.



Check out : https://github.com/ucb-bar/rocket-chip

Last time I complained here about the verification infrastructure of this project, someone gave that link.

I didn't like much of what I could find there.

What exactly are you trying to do?


I want to at the minimum compare the architectural state of the implementation on every retire with the ISA simulator (Spike).

In addition it would be good to have a set of assertions to maintain the sanity (read functional correctness) while experimenting with the design.

How are these implementations verified right now ? All I see are few assertions in chisel and small set of tests.


You can get a commit log (PC, inst, write-back address, write-back data) from Rocket to compare against Spike's commit log. It's not documented because the verification story is still in flux, and the commit log is fairly manual (since there will be many false positives).

Comparing a real CPU against an ISA simulator is VERY HARD. There's counter instructions, there's interrupts, timers will differ, multi-core will exhibit different (correct) answers, Rocket has out-of-order write-back+early commit, floating point registers are 65-bit recoded values, some (required) ambiguity in the spec that can't be reconciled easily (e.g., storing single-precision FP values using FSD puts undefined values in memory, the only requirement being that the value is properly restored by a corresponding FLD).

We also use a torture tester that we'll open source Soon (tm).


Thanks for the information. I understand its a hard problem but an essential one that needs a solution. It needs to be supported both in Chisel and with appropriate infrastructure to test and compare with the golden ISA model. Is there any one in the community who is actively working on the verification story ?


> Is there any one in the community who is actively working on the verification story ?

Not sure. I'd look out for videos to show up at the RISC-V workshop that's ongoing (http://riscv.org/workshop-jan2016.html).

The problem is verification is where the $$$ is, so even amongst people sharing their CPU source code, they're less willing to share the true value-provided of their efforts. A debug spec is being developed and will be added to Rocket-chip to make this problem easier.

With that said, MIT gave a good talk at the RISC-V workshop about their works on verification, and we open sourced our torture tester at (http://riscv.org/workshop-jan2016.html).



Not a lot of verification that I could find.

The tests are not extensive. Just hand written assembly code testing one thing at a time AFAIK. As someone who used to lead ASIC verification projects for a living, I expected a lot more at a minimum.

I don't know what the Chisel stuff checks. Chisel doesn't do anything at the simulation stage I believe.

I guess if you are just playing around with CPU designs, you can use this stuff.

I would never sign off on going to tape out with just this stuff though. Apparently they've taped out over 11 times though!

You want to run the RTL and compare against the ISA simulator? I think you're on your own...




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