Re: Zip GS questions

[pubpc1@library.ucla.edu]

Barry Rees <Barry.Rees@prodigy.net> wrote:
>pubpc1@library.ucla.edu wrote:
>> 
>
>> Have you tried to keep it at 16MHz, but changing the DIP config to >>read 16K of cache?  This tends to stabilize things and result in
>>surprisingly little degradation in performance.  Keep us apprised of
>>the progress!
>> 
>> :)
>> 
>> -Scott G.
>
>Scott,
>
>No, I hadn't tried that. Actually, my initial testing was at 16/64. That
>setup was almost unusable. However, I did cut the cache back to 32k and
>that proved to be 99% stable. But as I mentioned, I was still getting
>random crashes. It's an interesting point that you have brought up about
>cutting back on the cache. There was a drastic improvement going from 64
>to 32k during my testing. The 16/32 was almost ......... there.
>
>When I get back to testing, I'll keep in mind the 16k cache that you
>suggested. I'd like to get the 16 MHz setup working because it was
>INCREDIBLY fast. Question: With the (32k x 8) chips installed, can I
>still configure the DIP switches to only use 16k of the 64k installed
>cache?
>
>Thanks,
>
>Barry Rees


Barry, yes it will work.  I'm in the dark about how the Zip maps memory,
but from experimenting on the Zip, it seems that any time you have four
32k x 8 SRAMs installed, you can set the DIP switches to any of the
configurations from 8k all the way to 64k.

At 13.75MHz, I tested to see the speed differences between different
cache settings also.  I ran Ninjaforce's MegaDemo and watched the
scrolling rate.  At 8k cache, everything became jerky.  However, there
was not much difference at all between 16k, 32k, and 64k settings.
It is my belief that 16k is the "magic" number in terms of cache size.
It appears to be the cache size at which the caching becomes effective
and beyond that, increasing the cache size will not improve performance
that much more.  The speed for P8 and GS/OS programs like AppleWorks GS
also showed massive degradation in performance at 8k, but no noticeable
difference between the other (16k, 32k, and 64k) configurations.

So you might consider trying 16MHz/16k.  It will almost certainly be
faster than 12/64.  I hope you can get the board up and running at
16MHz (that's faster than most upgraded Zips run!) and post your
success story when you do.  Thanks.  :)

>Also, another problem I have is not having any oscillators between
>50MHz and 64MHz. So, I can't do any board testing anywhere between
>12.5 and 16 MHz.

The 55MHz and 60MHz oscillators are available from Digi-Key.  They
are the "half-size" kind, but the Zip can use both types.

:)

-Scott G.