Bump Verilator and use TestDriver.v as top

[abejgonzalez]

This removes the need for emulator.cc (a copy of Rocket Chip's emulator.cc only needed for Verilator) and instead uses the TestDriver.v file given by RC (this standardizes the simulator interface between VCS and Verilator). Additionally, this bumps to the newest version of Verilator for misc. bug fixes and perf. improvements. I've verified that the VCD and FST dumped out of this new flow works properly.

Related PRs / Issues:

Type of change:

• Bug fix
• New feature
• Other enhancement

Impact:

• RTL change
• Software change (RISC-V software)
• Build system change
• Other

Contributor Checklist:

• Did you set main as the base branch?
• Is this PR's title suitable for inclusion in the changelog and have you added a changelog:<topic> label?
• Did you state the type-of-change/impact?
• Did you delete any extraneous prints/debugging code?
• Did you mark the PR with a changelog: label?
• (If applicable) Did you update the conda .conda-lock.yml file if you updated the conda requirements file?
• (If applicable) Did you add documentation for the feature?
• (If applicable) Did you add a test demonstrating the PR?

• (If applicable) Did you mark the PR as Please Backport?

[abejgonzalez]

If this PR is fine, we can merge this in pre-release... but otherwise we can wait until after the release.

[jerryz123]

LGTM

[abejgonzalez]

This breaks FireSim. Postponing to after release.

[vighneshiyer]

Is there any performance degradation when using Verilog top vs C++ top with Verilator 5?

[abejgonzalez]

Is there any performance degradation when using Verilog top vs C++ top with Verilator 5?

I'll run a few quick tests. But I can't see anything online about performance regressions

[abejgonzalez]

My extremely scientific setup for performance regressions:

Config: MegaBoomConfig running run-bmark-tests (serially without any Scala compilation):

w/ 5.006 = 37m44s
w/ 4.226 = 41m7s

(Note that the 4.226 version might of had some contention (I was running a Scala compile on another tmux window))

IMO there isn't a large difference between the two so I think it's safe to say performance difference is negligible.