Re: Recode to Play MP3?

[mdj <mdj.mdj@gmail.com>]

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)

> 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.

> 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 :-)

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.

Matt