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Re: Recode to Play MP3?

mdj wrote:

On May 23, 7:40 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:



I'd say this was never done because you have to assume the expansion
space contains ROM in order to cache it. There must be at least one
case where a card used it for something else, like scratch RAM.


No, all RAM/ROM space is treated as read/write--it's just that ROM
space never gets "dirty"--but all that is moot since all caching is
write-through (as it needs to be for I/O registers and video memory).



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?


The only problem for a caching accelerator is when the contents of
a memory address--RAM or ROM--changes for some reason other than a
store instruction--like bank-switching or DMA.



That's more or less what I meant - at any given point in time you've
got no way to know what's going to be there on any given card, since
it's arbitrary.


But it's not ROM/RAM-related.


Not a problem--if you wanted to use a slow card, you would just mark
that slot "slow" to the accelerator.



True :-)



With all these changes in place, the CFFA would become one of the
fastest storage solutions, bested (probably) by the TurboIDE card, and
the RAMFast, but this would only be noticeable on multiblock
transfers, which only happen under GS/OS.


And maybe not even those, at least on a //e, since DMA is not allowed
with most accelerators--certainly not with a Zip Chip.



The TurboIDE reportedly does 300kb/s under ProDOS 8, but I'd rather
have the aforementioned CFFA mods + my accelerator any day :-)


So it uses DMA--I didn't know that.


I believe the Transwarp III claimed DMA compatibility, but those were
never released for public consumption.  Since the Zips cache is write-
through, it seems like an oversight that they didn't simply flag the
cache lines as invalid when DMA was activated. In the case of the
Transwarp I, it actually *is* a DMA peripheral.


The Zip Chip plugs into the processor socket, not the peripheral bus,
so it doesn't really know when DMA is activated.

-michael

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