class DummyPeripheral(Peripheral, Elaboratable):
    def __init__(self, *, **kwargs):
        super().__init__(**kwargs) # addr_width, data_width, alignment

        self._foo = self.csr(1, "r")
        self._bar = self.csr(1, "rw", addr=0x40)

    def elaborate(self, platform):
        m = Module()
        # ...
        return m