amaranth/tests/test_lib_coding.py

from nmigen.hdl import *
from nmigen.asserts import *
from nmigen.sim import *
from nmigen.lib.coding import *

from .utils import *


class EncoderTestCase(FHDLTestCase):
    def test_basic(self):
        enc = Encoder(4)
        def process():
            self.assertEqual((yield enc.n), 1)
            self.assertEqual((yield enc.o), 0)

            yield enc.i.eq(0b0001)
            yield Settle()
            self.assertEqual((yield enc.n), 0)
            self.assertEqual((yield enc.o), 0)

            yield enc.i.eq(0b0100)
            yield Settle()
            self.assertEqual((yield enc.n), 0)
            self.assertEqual((yield enc.o), 2)

            yield enc.i.eq(0b0110)
            yield Settle()
            self.assertEqual((yield enc.n), 1)
            self.assertEqual((yield enc.o), 0)

        sim = Simulator(enc)
        sim.add_process(process)
        sim.run()


class PriorityEncoderTestCase(FHDLTestCase):
    def test_basic(self):
        enc = PriorityEncoder(4)
        def process():
            self.assertEqual((yield enc.n), 1)
            self.assertEqual((yield enc.o), 0)

            yield enc.i.eq(0b0001)
            yield Settle()
            self.assertEqual((yield enc.n), 0)
            self.assertEqual((yield enc.o), 0)

            yield enc.i.eq(0b0100)
            yield Settle()
            self.assertEqual((yield enc.n), 0)
            self.assertEqual((yield enc.o), 2)

            yield enc.i.eq(0b0110)
            yield Settle()
            self.assertEqual((yield enc.n), 0)
            self.assertEqual((yield enc.o), 1)

        sim = Simulator(enc)
        sim.add_process(process)
        sim.run()


class DecoderTestCase(FHDLTestCase):
    def test_basic(self):
        dec = Decoder(4)
        def process():
            self.assertEqual((yield dec.o), 0b0001)

            yield dec.i.eq(1)
            yield Settle()
            self.assertEqual((yield dec.o), 0b0010)

            yield dec.i.eq(3)
            yield Settle()
            self.assertEqual((yield dec.o), 0b1000)

            yield dec.n.eq(1)
            yield Settle()
            self.assertEqual((yield dec.o), 0b0000)

        sim = Simulator(dec)
        sim.add_process(process)
        sim.run()


class ReversibleSpec(Elaboratable):
    def __init__(self, encoder_cls, decoder_cls, args):
        self.encoder_cls = encoder_cls
        self.decoder_cls = decoder_cls
        self.coder_args  = args

    def elaborate(self, platform):
        m = Module()
        enc, dec = self.encoder_cls(*self.coder_args), self.decoder_cls(*self.coder_args)
        m.submodules += enc, dec
        m.d.comb += [
            dec.i.eq(enc.o),
            Assert(enc.i == dec.o)
        ]
        return m


class HammingDistanceSpec(Elaboratable):
    def __init__(self, distance, encoder_cls, args):
        self.distance    = distance
        self.encoder_cls = encoder_cls
        self.coder_args  = args

    def elaborate(self, platform):
        m = Module()
        enc1, enc2 = self.encoder_cls(*self.coder_args), self.encoder_cls(*self.coder_args)
        m.submodules += enc1, enc2
        m.d.comb += [
            Assume(enc1.i + 1 == enc2.i),
            Assert(sum(enc1.o ^ enc2.o) == self.distance)
        ]
        return m


class GrayCoderTestCase(FHDLTestCase):
    def test_reversible(self):
        spec = ReversibleSpec(encoder_cls=GrayEncoder, decoder_cls=GrayDecoder, args=(16,))
        self.assertFormal(spec, mode="prove")

    def test_distance(self):
        spec = HammingDistanceSpec(distance=1, encoder_cls=GrayEncoder, args=(16,))
        self.assertFormal(spec, mode="prove")