ROHD Unit Testing Validation in Sequential

[quekyj]

How should I code my unit testing if the expected result is one clock later? Like how am I going to test for flip flop? What if the output is one clock or two clocks later?

[chykon]

Perhaps Simulator.tick() will work for your use case. Here is an example.

You can also use Simulator.registerAction(), but you may need to calculate the required time depending on the current Simulator.time and the clockPeriod parameter of SimpleClockGenerator.

[quekyj]

I see. Thanks for writing the example @chykon! Appreciate it. I wonder if it's possible to merge with dart unit test package: test. Currently, it's hard to trace for errors in Sequential(). Break point can't be set during the Simulation which is a pain for debugging.

[mkorbel1]

Here's an example where you can use await on the edges of the clock to drive stimulus and check values out of the flop.

import 'dart:async';
import 'package:rohd/rohd.dart';
import 'package:test/test.dart';

void main() {
  test('test flop', () async {
    final clk = SimpleClockGenerator(10).clk;
    final input = Logic(width: 8);
    final output = FlipFlop(clk, input).q;

    /// Prints the current state of the flop.
    void printFlop([String message = '']) {
      print('@${Simulator.time}:\t'
          ' input=${input.value}, output=${output.value}\t$message');
    }

    // set a max time in case something goes longer than expected
    Simulator.setMaxSimTime(100);

    // kick off the simulator, but dont wait for it, so we can do other async
    // stuff meanwhile.
    unawaited(Simulator.run());

    await clk.nextPosedge;
    input.put(0);

    // check after posedge sampling that the value matches expectations
    await clk.nextPosedge;
    printFlop('After sampling 0');
    expect(output.value.toInt(), 0);

    // drive a new value onto the flop
    input.put(0xa5);

    printFlop('After driving 0xa5, before posedge sampling');
    await clk.nextPosedge;
    printFlop('After driving 0xa5 and posedge sampling');
    expect(output.value.toInt(), 0xa5);

    // we're done, we can end the simulation
    Simulator.endSimulation();

    await Simulator.simulationEnded;
  });
}

The output of this test looks like this:

@15:	 input=8'h0, output=8'h0	After sampling 0
@15:	 input=8'ha5, output=8'h0	After driving 0xa5, before posedge sampling
@25:	 input=8'ha5, output=8'ha5	After driving 0xa5 and posedge sampling