Because of YosysHQ/yosys#1390, using a transparent port in AsyncFIFO,
instead of being a no-op (as the semantics of \TRANSPARENT would
require it to be in this case), results in a failure to infer BRAM.
This can be easily avoided by using a non-transparent port instead,
which produces the desirable result with Yosys. It does not affect
the semantics on Xilinx platforms, since the interaction between
the two ports in case of address collision is undefined in either
transparent (WRITE_FIRST) or non-transparent (READ_FIRST) case, and
the data out of the write port is not used at all.
Fixes#172.
This obscure functionality was likely only ever used in old MiSoC
code, and doesn't justify the added complexity. It was also not
provided (and could not be reasonably provided) in SyncFIFOBuffered,
which made its utility extremely marginal.
Without this register, static hazards in the encoder could cause
multiple encoder output bits to toggle, which would be incorrectly
sampled by the 2FF synchronizer.
Reported by @Wren6991.
The current behavior was introduced in 65702719, which was a wrong
fix for an issue that was actually fixed in 12e04e4e. This commit
effectively reverts 65702719 and 1782b841.