Re: CACHE????

[Michael Mahon <mahon@cup.hp.com>]

RUBYWAND wrote:
> 
> In article <31D9D33E.4144@cup.hp.com>, Michael Mahon <mahon@cup.hp.com>
> writes:
> 
> >....
> >It isn't ROM code--it's hardware!  This is in a PLA (or two--I don't
> >have one myself) and the cache addressing must be done on *every*
> >cycle of the faster clock.  ROM code is out of the question.
> >....
> >
> 
>      Yes; my mistake was in assuming that Zip-GS would have a nice,
> separate ROM which would contain 65C816 cache setup instructions. For
> example, the '816 would check dip switches and initialize latches to match
> size of on-board cache. Naturally, the actual cache address decoding would
> have to be handled by fast logic.
> 
>      As Neil pointed out, 'there ain't no ROM'-- at least, if there is, it
> is inside the ZipChip. If there is cache setup code executed by the '816
> and if the ZipChip can handle more than 64K cache (perhaps with a minor
> hardware add-on),  then an extension PROM should allow expanding cache
> size.
> 
>      Since so much of Zip-GS is in the ZipChip, it would help to know
> specifics of the IC's layout and operation. Some of this info is certain
> to be proprietary-- like PAL 'programming'. Still, if the IC is some kind
> of standard vendor-programmable micro-controller, then quite a few details
> may be available in some data book.

Straighten me out if I'm wrong, but I thought that a ZipGS was a board
containing:  a faster 65816, some medium fast cache SRAM, a little
"glue" logic, a clock oscillator, and a custom (programmed) PLA (one
or two, it doesn't matter).

If this is the case, then virtually *all* of what a ZipGS is and does
is a function of the data paths supported by the printed circuit and
the programmed function of the PLA(s).  If the number of pins and the
number of traces permit, then it would conceivably be possible to
address
larger cache/tag SRAMs, by using a differently programmed PLA.  If the
pins/traces are non-existent, then we're talking about a new design
*similar* to a ZipGS, but not a ZipGS.

Of course, there is also the issue of some patented intellectual
property in the design (which applies whether you make one for your
own use or to sell)...  ;-/

At this point is is a labor of love, not of sound business motivation,
to invest in such a design, fabricate it, and make it available.

-michael

---------------------------------
Just my opinion, etc...