from migen.fhdl.std import *
from migen.sim.generic import run_simulation

# Our simple counter, which increments at every cycle
# and prints its current value in simulation.
class Counter(Module):
    def __init__(self):
        self.count = Signal(4)

        # At each cycle, increase the value of the count signal.
        # We do it with convertible/synthesizable FHDL code.
        self.sync += self.count.eq(self.count + 1)

    # This function will be called at every cycle.
    def do_simulation(self, selfp):
        # Simply read the count signal and print it.
        # The output is:
        # Count: 0
        # Count: 1
        # Count: 2
        # ...
        print("Count: " + str(selfp.count))

if __name__ == "__main__":
    dut = Counter()
    # Since we do not use StopSimulation, limit the simulation
    # to some number of cycles.
    run_simulation(dut, ncycles=20)