X-Git-Url: https://git.libre-soc.org/?a=blobdiff_plain;f=litex%2Fgen%2Fgenlib%2Fcdc.py;h=3ba1a2627d237579a0eef79b9bd21af72f08f8ea;hb=212e1a7076116a8322d1b2edf51200cfc5c116e7;hp=7f72b471985c40a98044b2656f3e4977fba8ca22;hpb=677243bd8c132113bdb59e4c7531134c5a469ee8;p=litex.git

diff --git a/litex/gen/genlib/cdc.py b/litex/gen/genlib/cdc.py
index 7f72b471..3ba1a262 100644
--- a/litex/gen/genlib/cdc.py
+++ b/litex/gen/genlib/cdc.py
@@ -1,22 +1,17 @@
+"""
+Clock domain crossing module
+"""
+from math import gcd
+
 from litex.gen.fhdl.structure import *
 from litex.gen.fhdl.module import Module
 from litex.gen.fhdl.specials import Special, Memory
 from litex.gen.fhdl.bitcontainer import value_bits_sign
+from litex.gen.fhdl.decorators import ClockDomainsRenamer
 from litex.gen.genlib.misc import WaitTimer
 from litex.gen.genlib.resetsync import AsyncResetSynchronizer
 
 
-class NoRetiming(Special):
-    def __init__(self, reg):
-        Special.__init__(self)
-        self.reg = reg
-
-    # do nothing
-    @staticmethod
-    def lower(dr):
-        return Module()
-
-
 class MultiRegImpl(Module):
     def __init__(self, i, o, odomain, n):
         self.i = i
@@ -24,7 +19,8 @@ class MultiRegImpl(Module):
         self.odomain = odomain
 
         w, signed = value_bits_sign(self.i)
-        self.regs = [Signal((w, signed)) for i in range(n)]
+        self.regs = [Signal((w, signed), reset_less=True)
+                for i in range(n)]
 
         ###
 
@@ -34,7 +30,8 @@ class MultiRegImpl(Module):
             sd += reg.eq(src)
             src = reg
         self.comb += self.o.eq(src)
-        self.specials += [NoRetiming(reg) for reg in self.regs]
+        for reg in self.regs:
+            reg.attr.add("no_retiming")
 
 
 class MultiReg(Special):
@@ -71,9 +68,9 @@ class PulseSynchronizer(Module):
 
         ###
 
-        toggle_i = Signal()
-        toggle_o = Signal()
-        toggle_o_r = Signal()
+        toggle_i = Signal(reset_less=True)
+        toggle_o = Signal()  # registered reset_less by MultiReg
+        toggle_o_r = Signal(reset_less=True)
 
         sync_i = getattr(self.sync, idomain)
         sync_o = getattr(self.sync, odomain)
@@ -92,7 +89,7 @@ class BusSynchronizer(Module):
     ``MultiReg``)."""
     def __init__(self, width, idomain, odomain, timeout=128):
         self.i = Signal(width)
-        self.o = Signal(width)
+        self.o = Signal(width, reset_less=True)
 
         if width == 1:
             self.specials += MultiReg(self.i, self.o, odomain)
@@ -104,16 +101,18 @@ class BusSynchronizer(Module):
             sync_i += starter.eq(0)
             self.submodules._ping = PulseSynchronizer(idomain, odomain)
             self.submodules._pong = PulseSynchronizer(odomain, idomain)
-            self.submodules._timeout = WaitTimer(timeout)
+            self.submodules._timeout = ClockDomainsRenamer(idomain)(
+                WaitTimer(timeout))
             self.comb += [
                 self._timeout.wait.eq(~self._ping.i),
                 self._ping.i.eq(starter | self._pong.o | self._timeout.done),
                 self._pong.i.eq(self._ping.i)
             ]
 
-            ibuffer = Signal(width)
-            obuffer = Signal(width)
+            ibuffer = Signal(width, reset_less=True)
+            obuffer = Signal(width)  # registered reset_less by MultiReg
             sync_i += If(self._pong.o, ibuffer.eq(self.i))
+            ibuffer.attr.add("no_retiming")
             self.specials += MultiReg(ibuffer, obuffer, odomain)
             sync_o += If(self._ping.o, self.o.eq(obuffer))
 
@@ -142,6 +141,20 @@ class GrayCounter(Module):
         ]
 
 
+class GrayDecoder(Module):
+    def __init__(self, width):
+        self.i = Signal(width)
+        self.o = Signal(width, reset_less=True)
+
+        # # #
+
+        o_comb = Signal(width)
+        self.comb += o_comb[-1].eq(self.i[-1])
+        for i in reversed(range(width-1)):
+            self.comb += o_comb[i].eq(o_comb[i+1] ^ self.i[i])
+        self.sync += self.o.eq(o_comb)
+
+
 class ElasticBuffer(Module):
     def __init__(self, width, depth, idomain, odomain):
         self.din = Signal(width)
@@ -184,3 +197,57 @@ class ElasticBuffer(Module):
             rdport.adr.eq(rdpointer),
             self.dout.eq(rdport.dat_r)
         ]
+
+
+def lcm(a, b):
+    """Compute the lowest common multiple of a and b"""
+    return (a*b)//gcd(a, b)
+
+
+class Gearbox(Module):
+    def __init__(self, iwidth, idomain, owidth, odomain):
+        self.i = Signal(iwidth)
+        self.o = Signal(owidth, reset_less=True)
+
+        # # #
+
+        rst = Signal()
+        cd_write = ClockDomain()
+        cd_read = ClockDomain()
+        self.comb += [
+            rst.eq(ResetSignal(idomain) | ResetSignal(odomain)),
+            cd_write.clk.eq(ClockSignal(idomain)),
+            cd_read.clk.eq(ClockSignal(odomain)),
+            cd_write.rst.eq(rst),
+            cd_read.rst.eq(rst)
+        ]
+        self.clock_domains += cd_write, cd_read
+
+        storage = Signal(2*lcm(iwidth, owidth), reset_less=True)
+        wrchunks = len(storage)//iwidth
+        rdchunks = len(storage)//owidth
+        wrpointer = Signal(max=wrchunks, reset=0 if iwidth > owidth else wrchunks//2)
+        rdpointer = Signal(max=rdchunks, reset=rdchunks//2 if iwidth > owidth else 0)
+
+        self.sync.write += \
+            If(wrpointer == wrchunks-1,
+                wrpointer.eq(0)
+            ).Else(
+                wrpointer.eq(wrpointer + 1)
+            )
+        cases = {}
+        for i in range(wrchunks):
+            cases[i] = [storage[iwidth*i:iwidth*(i+1)].eq(self.i)]
+        self.sync.write += Case(wrpointer, cases)
+
+
+        self.sync.read += \
+            If(rdpointer == rdchunks-1,
+                rdpointer.eq(0)
+            ).Else(
+                rdpointer.eq(rdpointer + 1)
+            )
+        cases = {}
+        for i in range(rdchunks):
+            cases[i] = [self.o.eq(storage[owidth*i:owidth*(i+1)])]
+        self.sync.read += Case(rdpointer, cases)
\ No newline at end of file