Commit 210ba91d authored by Florent Kermarrec's avatar Florent Kermarrec Committed by Sebastien Bourdeauducq
Browse files

migen/genlib/cdc: fix BusSynchronizer

ping/pong token can be lost when:
- source clock domain starts before destination clock domain.
- a clock domain stops.

This fix add a timeout to detect such situation and create another token.
parent 07efe9d7
......@@ -2,6 +2,7 @@ from migen.fhdl.std import *
from migen.fhdl.bitcontainer import value_bits_sign
from migen.fhdl.specials import Special
from migen.fhdl.tools import list_signals
from migen.genlib.misc import WaitTimer
class NoRetiming(Special):
......@@ -88,7 +89,7 @@ class BusSynchronizer(Module):
Ensures that all the bits form a single word that was present
synchronously in the input clock domain (unlike direct use of
``MultiReg``)."""
def __init__(self, width, idomain, odomain):
def __init__(self, width, idomain, odomain, timeout=128):
self.i = Signal(width)
self.o = Signal(width)
......@@ -102,8 +103,10 @@ 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.comb += [
self._ping.i.eq(starter | self._pong.o),
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)
]
......
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