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fhdl.ir: a subfragment's input that we don't drive is also our input.

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whitequark 2018-12-13 11:50:56 +00:00
parent bb04c9e0da
commit 9661e897e6
2 changed files with 16 additions and 1 deletions
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4
nmigen/fhdl/ir.py
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@ -152,8 +152,10 @@ class Fragment:
# to provide. If the subfragment is not driving it, it will silently ignore it.
sub_ins, sub_outs = subfrag._propagate_ports(ports=self_used | ports)
# Refine the input port approximation: if a subfragment is driving a signal,
# it is definitely not our input.
# it is definitely not our input. But, if a subfragment requires a signal as an input,
# and we aren't driving it, it has to be our input as well.
ins -= sub_outs
ins |= sub_ins - self_driven
# Refine the output port approximation: if a subfragment is driving a signal,
# and we're asked to provide it, we can provide it now.
outs |= ports & sub_outs