litex/migen/genlib/cdc.py

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from migen.fhdl.structure import *
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from migen.fhdl.module import Module
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from migen.fhdl.specials import Special
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from migen.fhdl.tools import list_signals
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class NoRetiming(Special):
def __init__(self, reg):
Special.__init__(self)
self.reg = reg
# do nothing
@staticmethod
def lower(dr):
return Module()
class MultiRegImpl(Module):
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def __init__(self, i, o, odomain, n):
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self.i = i
self.o = o
self.odomain = odomain
w, signed = value_bits_sign(self.i)
self.regs = [Signal((w, signed)) for i in range(n)]
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###
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src = self.i
for reg in self.regs:
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sd = getattr(self.sync, self.odomain)
sd += reg.eq(src)
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src = reg
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self.comb += self.o.eq(src)
self.specials += [NoRetiming(reg) for reg in self.regs]
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class MultiReg(Special):
def __init__(self, i, o, odomain="sys", n=2):
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Special.__init__(self)
self.i = i
self.o = o
self.odomain = odomain
self.n = n
def iter_expressions(self):
yield self, "i", SPECIAL_INPUT
yield self, "o", SPECIAL_OUTPUT
def rename_clock_domain(self, old, new):
Special.rename_clock_domain(self, old, new)
if self.odomain == old:
self.odomain = new
def list_clock_domains(self):
r = Special.list_clock_domains(self)
r.add(self.odomain)
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return r
@staticmethod
def lower(dr):
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return MultiRegImpl(dr.i, dr.o, dr.odomain, dr.n)
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class PulseSynchronizer:
def __init__(self, idomain, odomain):
self.idomain = idomain
self.odomain = odomain
self.i = Signal()
self.o = Signal()
def get_fragment(self):
toggle_i = Signal()
toggle_o = Signal()
toggle_o_r = Signal()
sync_i = [
If(self.i, toggle_i.eq(~toggle_i))
]
sync_o = [
toggle_o_r.eq(toggle_o)
]
comb = [
self.o.eq(toggle_o ^ toggle_o_r)
]
return Fragment(comb,
{self.idomain: sync_i, self.odomain: sync_o},
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specials={MultiReg(toggle_i, toggle_o, self.odomain)})
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class GrayCounter(Module):
def __init__(self, width):
self.ce = Signal()
self.q = Signal(width)
self.q_next = Signal(width)
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self.q_binary = Signal(width)
self.q_next_binary = Signal(width)
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###
self.comb += [
If(self.ce,
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self.q_next_binary.eq(self.q_binary + 1)
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).Else(
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self.q_next_binary.eq(self.q_binary)
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),
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self.q_next.eq(self.q_next_binary ^ self.q_next_binary[1:])
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]
self.sync += [
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self.q_binary.eq(self.q_next_binary),
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self.q.eq(self.q_next)
]