forked from M-Labs/artiq
67 lines
2.1 KiB
Python
67 lines
2.1 KiB
Python
from migen import *
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from migen.genlib.cdc import *
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__all__ = ["GrayCodeTransfer", "RTIOCounter", "BlindTransfer"]
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# note: transfer is in rtio/sys domains and not affected by the reset CSRs
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class GrayCodeTransfer(Module):
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def __init__(self, width):
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self.i = Signal(width) # in rtio domain
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self.o = Signal(width) # in sys domain
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# # #
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# convert to Gray code
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value_gray_rtio = Signal(width)
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self.sync.rtio += value_gray_rtio.eq(self.i ^ self.i[1:])
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# transfer to system clock domain
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value_gray_sys = Signal(width)
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value_gray_rtio.attr.add("no_retiming")
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self.specials += MultiReg(value_gray_rtio, value_gray_sys)
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# convert back to binary
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value_sys = Signal(width)
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self.comb += value_sys[-1].eq(value_gray_sys[-1])
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for i in reversed(range(width-1)):
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self.comb += value_sys[i].eq(value_sys[i+1] ^ value_gray_sys[i])
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self.sync += self.o.eq(value_sys)
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class RTIOCounter(Module):
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def __init__(self, width):
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self.width = width
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# Timestamp counter in RTIO domain
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self.value_rtio = Signal(width)
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# Timestamp counter resynchronized to sys domain
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# Lags behind value_rtio, monotonic and glitch-free
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self.value_sys = Signal(width)
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# # #
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# note: counter is in rtio domain and never affected by the reset CSRs
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self.sync.rtio += self.value_rtio.eq(self.value_rtio + 1)
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gt = GrayCodeTransfer(width)
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self.submodules += gt
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self.comb += gt.i.eq(self.value_rtio), self.value_sys.eq(gt.o)
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class BlindTransfer(Module):
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def __init__(self):
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self.i = Signal()
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self.o = Signal()
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ps = PulseSynchronizer("rio", "rsys")
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ps_ack = PulseSynchronizer("rsys", "rio")
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self.submodules += ps, ps_ack
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blind = Signal()
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self.sync.rio += [
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If(self.i, blind.eq(1)),
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If(ps_ack.o, blind.eq(0))
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]
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self.comb += [
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ps.i.eq(self.i & ~blind),
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ps_ack.i.eq(ps.o),
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self.o.eq(ps.o)
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]
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