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Re: Recode to Play MP3?

mdj wrote:

On May 24, 10:25 am, "Michael J. Mahon" <mjma...@aol.com> wrote:



The Transwarp only writes through when it has to (to the above
mentioned areas)


That's interesting...  So most of the RAM is "stale" when running
a TransWarp?  I wonder how much speed improvement this buys them?



It's difficult to say. The Transwarp certainly performs better at a
given speed than the Zip, but this is primarily due to never having to
invalidate cache for Main/Aux/ROM.


The Zip has 8KB of direct-mapped cache, with 8-bit tags, so there are
13 real address bits for the cache, and 3 bits (per 64KB) in the tag,
leaving 5 additional tag bits, to support up to 32x64KB or 2MB of
RAM.  It tracks RAMworks-style AUX bank switching.

Since it's write-through, there's never a "dirty" cache byte, and
the cache is only used to accelerate reads (which are the vast majority
of accesses).

Cache is never invalidated, but when executing "synchronous sequences"
a cache miss is forced for both reads and writes.


Certainly in any application where there's a lot of moving about of
data, like say a large AppleWorks word processor document, the
Transwarp feels a little snappier then a 4Mhz Zip.


Some timing tests may be in order...

There's no doubt that the Zip wins big on the "bang per milliwatt"
scale.  ;-)


The biggest improvement probably comes from never having to write
through to the zero page or the stack, the rest is probably
negligible.


Given the predominance of write activity to those pages, particuarly
page 0, I agree.


I've often been tempted to fit a faster '02 and RAM to the Transwarp
and seeing if I can 'overclock' it. The primary clock seems to be
derived by doing a divide by 2 on the 7Mhz signal, so it's easy enough
to bypass the divider.

I'm a little concerned by the potential power consumption, and thus
heat that would result from it though and I'm not keen to bake one of
the GALS


Right--it alrady runs warm enough without adding a factor of two
in frequency.  ;-)  The TransWarp is one card that is *way* beyond
the Apple slot power design specs.

-michael

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Home page:  http://members.aol.com/MJMahon/

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