From: whitequark Date: Sun, 20 Jan 2019 02:20:34 +0000 (+0000) Subject: lib.coding: add GrayEncoder and GrayDecoder. X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=4c5ac222e7a1901429d77807265481e6de203be6;p=nmigen.git lib.coding: add GrayEncoder and GrayDecoder. Unlike the Migen ones, these are purely combinatorial. --- diff --git a/nmigen/lib/coding.py b/nmigen/lib/coding.py index 081858b..653882f 100644 --- a/nmigen/lib/coding.py +++ b/nmigen/lib/coding.py @@ -3,6 +3,13 @@ from .. import * +__all__ = [ + "Encoder", "Decoder", + "PriorityEncoder", "PriorityDecoder", + "GrayEncoder", "GrayDecoder", +] + + class Encoder: """Encode one-hot to binary. @@ -121,3 +128,59 @@ class PriorityDecoder(Decoder): Identical to :class:`Decoder`. """ + + +class GrayEncoder: + """Encode binary to Gray code. + + Parameters + ---------- + width : int + Bit width. + + Attributes + ---------- + i : Signal(width), in + Input natural binary. + o : Signal(width), out + Encoded Gray code. + """ + def __init__(self, width): + self.width = width + + self.i = Signal(width) + self.o = Signal(width) + + def get_fragment(self, platform): + m = Module() + m.d.comb += self.o.eq(self.i ^ self.i[1:]) + return m.lower(platform) + + +class GrayDecoder: + """Decode Gray code to binary. + + Parameters + ---------- + width : int + Bit width. + + Attributes + ---------- + i : Signal(width), in + Input Gray code. + o : Signal(width), out + Decoded natural binary. + """ + def __init__(self, width): + self.width = width + + self.i = Signal(width) + self.o = Signal(width) + + def get_fragment(self, platform): + m = Module() + m.d.comb += self.o[-1].eq(self.i[-1]) + for i in reversed(range(self.width - 1)): + m.d.comb += self.o[i].eq(self.o[i + 1] ^ self.i[i]) + return m.lower(platform) diff --git a/nmigen/test/test_lib_coding.py b/nmigen/test/test_lib_coding.py index c535c79..53f2b8b 100644 --- a/nmigen/test/test_lib_coding.py +++ b/nmigen/test/test_lib_coding.py @@ -1,5 +1,6 @@ from .tools import * from ..hdl.ast import * +from ..hdl.dsl import * from ..back.pysim import * from ..lib.coding import * @@ -79,3 +80,47 @@ class DecoderTestCase(FHDLTestCase): sim.add_process(process) sim.run() + + +class ReversibleSpec: + def __init__(self, encoder_cls, decoder_cls, args): + self.encoder_cls = encoder_cls + self.decoder_cls = decoder_cls + self.coder_args = args + + def get_fragment(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.lower(platform) + + +class HammingDistanceSpec: + def __init__(self, distance, encoder_cls, args): + self.distance = distance + self.encoder_cls = encoder_cls + self.coder_args = args + + def get_fragment(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.lower(platform) + + +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")