verilator: broken support for Verilog $time system task

[terpstra]

verilator: broken support for Verilog $time system task

[terpstra]

@jackkoenig This issue is actually blocking me right now. Aside from manually hacking this file in my clone of the repository, is there any way I can override this so as to continue to make progress with the unfixed chiseltest? I noticed that, unfortunately, VerilatorSimulator.generateHarness is private. :-/

[terpstra]

It seems that now one is supposed to use timeInc, which would help here, since the simulator state is not a singleton. Not sure how to do this, though.

[terpstra]

verilator/verilator#2660 (comment)

[terpstra]

Find the fix below. I'd push it into a PR, but I don't have commit rights.

From 2d0144262231b807acb3aab8463763d6af7f2d60 Mon Sep 17 00:00:00 2001
From: "Wesley W. Terpstra" <[email protected]>
Date: Thu, 7 Jul 2022 22:32:27 -0700
Subject: [PATCH] verilator: fix $time

We need to set the time on the simulator context.
Otherwise, $time returns 0 all the time.
---
 .../simulator/jna/VerilatorCppJNAHarnessGenerator.scala         | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/main/scala/chiseltest/simulator/jna/VerilatorCppJNAHarnessGenerator.scala b/src/main/scala/chiseltest/simulator/jna/VerilatorCppJNAHarnessGenerator.scala
index 3e32a65..c4016e9 100644
--- a/src/main/scala/chiseltest/simulator/jna/VerilatorCppJNAHarnessGenerator.scala
+++ b/src/main/scala/chiseltest/simulator/jna/VerilatorCppJNAHarnessGenerator.scala
@@ -258,12 +258,14 @@ static sim_state* create_sim_state() {
                          |
                          |static int64_t _step(VERILATED_C* tfp, TOP_CLASS* top, vluint64_t& main_time) {
                          |    $clockLow
+                         |    Verilated::defaultContextp()->time(main_time);
                          |    top->eval();
                          |#if VM_TRACE
                          |    if (tfp) tfp->dump(main_time);
                          |#endif
                          |    main_time++;
                          |    $clockHigh
+                         |    Verilated::defaultContextp()->time(main_time);
                          |    top->eval();
                          |#if VM_TRACE
                          |    if (tfp) tfp->dump(main_time);
-- 
2.27.0

[terpstra]

I tried upgrading the code to use a locally allocated context, but there were too many call sites into the test harness where you did not have a sim_state pointer, so I gave up and took the easy fix.