class FrequencyMeasurement(Module, AutoCSR):
    def __init__(self, pulse):
        self._period = CSRStatus(32)

        # # #

        # compute period (unit = sys_clk ticks)
        self.submodules.counter = counter = Counter(32)
        self.comb += [
            counter.ce.eq(1),
            counter.reset.eq(pulse)
        ]
        self.sync += [
            If(counter.reset,
                self._period.status.eq(counter.value)
            )
        ]