the original 6600 scoreboard is single-signal request-ack protection
for multiple reads on the regfile. overporting is then added so that
multiple batches of ALUs can simultaneously read (and write) to the
we cannot do massive-way regfile porting.
additionally we need to do *different* regfiles for POWER: one of
these is the "Branch Control" Regfile, including CR0, CTR and other
therefore it becomes more important to have fine-grain control over
the regfile, meaning that multiple go-read/req and go-write/req
wires are needed per FunctionUnit.