[Open-graphics] HQ stub in place

[Petter Urkedal]

On 2008-07-30, Petter Urkedal wrote:
> One thing which is not clear to me is what to register at what needs to
> be combinatorial.  I think the critical part is reads.  The input ports
> needs to be decoded from the port address (val_or_addr) and fed back to
> HQ and multiplexed into wb_val_o in one cycle, or is there another way?

Correction:  The output wb_val_o is already muxed from data registered
in oga1hq_stg4_memio.  If we can afford another level of logic here, we
can register the read-data before passing it back to HQ.  (It may be
tight on timing, since wb_val_o goes to register forwarding.)
Otherwise, we could try to pass it combinatorially as a replacement for
the current input_port placeholder.