lib.coding: port from Migen.

nmigen/lib/coding.py

@@ -0,0 +1,118 @@
+"""Encoders and decoders between binary and one-hot representation."""
+
+from .. import *
+
+
+class Encoder:
+    """Encode one-hot to binary.
+
+    If one bit in ``i`` is asserted, ``n`` is low and ``o`` indicates the asserted bit.
+    Otherwise, ``n`` is high and ``o`` is ``0``.
+
+    Parameters
+    ----------
+    width : int
+        Bit width of the input
+
+    Attributes
+    ----------
+    i : Signal(width), in
+        One-hot input.
+    o : Signal(max=width), out
+        Encoded binary.
+    n : Signal, out
+        Invalid: either none or multiple input bits are asserted.
+    """
+    def __init__(self, width):
+        self.i = Signal(width)
+        self.o = Signal(max=max(2, width))
+        self.n = Signal()
+
+    def get_fragment(self, platform):
+        m = Module()
+        with m.Switch(self.i):
+            for j in range(len(self.i)):
+                with m.Case(1 << j):
+                    m.d.comb += self.o.eq(j)
+            with m.Case():
+                m.d.comb += self.n.eq(1)
+        return m.lower(platform)
+
+
+class PriorityEncoder:
+    """Priority encode requests to binary.
+
+    If any bit in ``i`` is asserted, ``n`` is low and ``o`` indicates the least significant
+    asserted bit.
+    Otherwise, ``n`` is high and ``o`` is ``0``.
+
+    Parameters
+    ----------
+    width : int
+        Bit width of the input.
+
+    Attributes
+    ----------
+    i : Signal(width), in
+        Input requests.
+    o : Signal(max=width), out
+        Encoded binary.
+    n : Signal, out
+        Invalid: no input bits are asserted.
+    """
+    def __init__(self, width):
+        self.i = Signal(width)
+        self.o = Signal(max=max(2, width))
+        self.n = Signal()
+
+    def get_fragment(self, platform):
+        m = Module()
+        for j, b in enumerate(reversed(self.i)):
+            with m.If(b):
+                m.d.comb += self.o.eq(j)
+        m.d.comb += self.n.eq(self.i == 0)
+        return m.lower(platform)
+
+
+class Decoder:
+    """Decode binary to one-hot.
+
+    If ``n`` is low, only the ``i``th bit in ``o`` is asserted.
+    If ``n`` is high, ``o`` is ``0``.
+
+    Parameters
+    ----------
+    width : int
+        Bit width of the output.
+
+    Attributes
+    ----------
+    i : Signal(max=width), in
+        Input binary.
+    o : Signal(width), out
+        Decoded one-hot.
+    n : Signal, in
+        Invalid, no output bits are to be asserted.
+    """
+    def __init__(self, width):
+        self.i = Signal(max=max(2, width))
+        self.n = Signal()
+        self.o = Signal(width)
+
+    def get_fragment(self, platform):
+        m = Module()
+        with m.Switch(self.i):
+            for j in range(len(self.o)):
+                with m.Case(j):
+                    m.d.comb += self.o.eq(1 << j)
+            with m.Case():
+                with m.If(self.n):
+                    m.d.comb += self.o.eq(0)
+        return m.lower(platform)
+
+
+class PriorityDecoder(Decoder):
+    """Decode binary to priority request.
+
+    Identical to :class:`Decoder`.
+    """