Verilator and Yosys support broken

[zyedidia]

I've been trying to use the microwatt.v and microwatt-verilator targets in the makefile, but it seems like both are broken. The microwatt.v file produced by Yosys generates invalid Verilog, which Yosys itself cannot read back. The issue seems to be caused by Yosys generating a few statements of the form assign "" = "". Should I report this directly to Yosys?

After removing those lines, Yosys can read the file in but Verilator still gives the error:

%Error: microwatt.v:203:3: Cannot find file containing module: 'EHXPLLL'

along with some warnings (LITENDIAN, and PINMISSING) though perhaps these can be ignored.

Are these targets supposed to be working, or are they still in-progress?

I'm using versions built fairly recently from source: Yosys 0.9+3672, Verilator 4.203 devel rev v4.202-56-g1f331bd9, and GHDL 2.0.0-dev (1.0.0.r333.g17ddaa0d).

[umarcor]

@zyedidia it seems that the Yosys -> Verilog -> Verilator -> Simulation workflow is not used/test in CI. The generation of the verilog source is tested only: https://github.com/antonblanchard/microwatt/blob/master/.github/workflows/test.yml#L88.

However, using git blame as a reference (https://github.com/antonblanchard/microwatt/blame/f9654428ff28744dcf1ad4e7fe43604415689f36/Makefile#L196), it seems that @antonblanchard uses verilator, because it was modified some months ago: https://github.com/antonblanchard/microwatt/pull/286/files.

According to https://github.com/antonblanchard/microwatt/commit/df8e1ca2a7a4c59ebaf4fb09a485a641c99c7c80, you need to set FPGA_TARGET=verilator. That would explain why you are having problems with EHXPLL (the default target is the OrangeCrab/ECP5): https://github.com/antonblanchard/microwatt/blob/master/Makefile#L144).

[antonblanchard]

Thanks for investigating @umarcor! You are correct in that FPGA_TARGET=verilator needs to be set. This is confusing, and the Makefile is a bit of a mess, but I had hoped we'd be able to drive ghdl and yosys with fusesoc. Hopefully one day.

We now have a CI test that builds a verilator binary and runs micropython.

[umarcor]

@antonblanchard, precisely microwatt is one of the projects I'm using as a reference for OSVB: Core and when working on the ProjectModel in EDA² (edaa-org.github.io). The Makefile and .core files in this repository are rather challenging, so they are a pretty strong test for any project trying to deal with "HDL and EDA tooling". Very particularly, how you combine GHL + Verilator and GHDL + Yosys + Verilator is very valuable knowledge.

That is also related to VUnit, which was contributed here by @LarsAsplund a few months ago. We are looking into some nicer integration of VUnit with FuseSoc/Edalize. That's actually what the pyCAPI proof-of-concept in OSVB is about.

/cc @Paebbels @olofk