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Re: iTunes - Can I create multiple profiles?

aiiadict@gmail.com wrote:

Michael J. Mahon wrote:


A fundamental problem is that DAC522 *completely* occupies the
processor while playing, so there would be no way to read in another
memory-load without stopping the playing.



could you modify the firmware of Alex Freed's disk emulator
card to operate like this:

1-add "streaming" mode

DAC program:

instead of loading from RAM, load from Cx00 (with card in "STREAMING"
mode)
the byte at Cx00 is the beginning of the stream file....

when Cx00 is accessed, the card immediately gets the next byte from the
file,
and puts it at Cx00

the next time DAC needs data, it's ready at Cx00.

no extra CPU time needed...  Just need to update the disk emulators
firmware, and modify the DAC code to look at Cx00 instead of loading
from RAM....  you'd probably end up with more cycles to play with,

stream-mode- on disk emulator card
LDA Cx00 - 3 cycles to load the next byte

DAC currently:
LDA ABCD,x ?? 3 or more cycles.. don't have charts handy
plus some logic to increment X,
plus some logic to increment to next page in RAM


Yes, this approach could work (in fact it's on my list of things
to do using the Slinky memory expansion card) as long as the data
load is almost exactly like a load from memory (exactly is even
better ;-).

Since the "address" register in this case is on the card, not in
the Apple, it would be possible to play *very* long sounds.

End detection would probably have to be a $00 in the data stream,
or there would have to be some condition created by the card when
a stream was exhausted.  The 3- or more byte arithmetic required
to have the processor count the stream would be hard to accomodate.

-michael

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