On 2007-08-12, Timothy Normand Miller wrote:
> Also, on a related note, I'm working on doing synthesis of hq today.

Sounds good.

> One thing I noticed is that the top-level module has no outputs.  If

Yes, address and data lines for IO ports are not yet routed out from
stage 4.  Before we do that, we need to decide on the structure of the
address space.  Observing that our immediates are 15 bit signed
integers, I suggest we route out negative addresses and keep positive
addresses for scratch.  The initial block of N IO-ports will be
addressed from -N to -1 and the scratch space goes from 0 to 512.  That
way we can add internal scratch or additional IO ports while retaining
machine-code compatibility, and at the same time be able to address
everything with immediates.  We could do it the other way around, but
I'm thinking it's less confusing for the programmer to work on positive
addresses for scratch, whereas IO ports are just predefined constants
anyway.
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