[ESI Runtime][Verilator] Option to slow down the sim

Add a 'DEBUG_PERIOD' option to slow down the simulation. Useful in
waveform debugging a fast simulation.

lib/Dialect/ESI/runtime/cosim_dpi_server/driver.cpp

@@ -34,6 +34,7 @@
 
 #include "signal.h"
 #include <iostream>
+#include <thread>
 
 vluint64_t timeStamp;
 
@@ -54,6 +55,14 @@ int main(int argc, char **argv) {
   auto &dut = *new CLASSNAME(V, TOP_MODULE)();
   char *waveformFile = getenv("SAVE_WAVE");
 
+  char *periodStr = getenv("DEBUG_PERIOD");
+  unsigned debugPeriod = 0;
+  if (periodStr) {
+    debugPeriod = std::stoi(periodStr);
+    std::cout << "[driver] Setting debug period to " << debugPeriod
+              << std::endl;
+  }
+
   VerilatedVcdC *tfp = nullptr;
   if (waveformFile) {
 #ifdef TRACE
@@ -97,6 +106,8 @@ int main(int argc, char **argv) {
     dut.clk = !dut.clk;
     if (tfp)
       tfp->dump(timeStamp);
+    if (debugPeriod)
+      std::this_thread::sleep_for(std::chrono::milliseconds(debugPeriod));
   }
 
   // Tell the simulator that we're going to exit. This flushes the output(s) and

lib/Dialect/ESI/runtime/cosim_dpi_server/esi-cosim.py

@@ -157,6 +157,8 @@ def run(self, inner_command: str, gui: bool = False) -> int:
       simEnv = Simulator.get_env()
       if self.debug:
         simEnv["COSIM_DEBUG_FILE"] = "cosim_debug.log"
+        # Slow the simulation down to one tick per millisecond.
+        simEnv["DEBUG_PERIOD"] = "1"
       simProc = subprocess.Popen(self.run_command(gui),
                                  stdout=simStdout,
                                  stderr=simStderr,