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wrpll: babysit Vivado DSP retiming 

Design now passes timing.
This commit is contained in:
Sebastien Bourdeauducq 2020-10-08 17:51:27 +08:00
parent 7dfb4af682
commit 07d43b6e5f
1 changed files with 21 additions and 3 deletions
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24
artiq/gateware/drtio/wrpll/thls.py
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@ -403,10 +403,28 @@ class OpUnit(BaseUnit):
def __init__(self, op, data_width, stages):
BaseUnit.__init__(self, data_width)
o = op(self.i0, self.i1)
stb_o = self.stb_i
for i in range(stages):
if stages > 1:
# Vivado backward retiming for DSP does not work correctly if DSP inputs
# are not registered.
i0 = Signal.like(self.i0)
i1 = Signal.like(self.i1)
stb_i = Signal()
self.sync += [
i0.eq(self.i0),
i1.eq(self.i1),
stb_i.eq(self.stb_i)
]
output_stages = stages - 1
else:
i0, i1, stb_i = self.i0, self.i1, self.stb_i
output_stages = stages
o = op(i0, i1)
stb_o = stb_i
for i in range(output_stages):
n_o = Signal(data_width)
if stages > 1:
n_o.attr.add(("retiming_backward", 1))
n_stb_o = Signal()
self.sync += [
n_o.eq(o),