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Re: Pseudo-disk *almost* ready for the big time.

Alex Freed wrote:

"sicklittlemonkey" <Nick.Westgate@gmail.com> wrote in message
1161755334.468452.170750@m7g2000cwm.googlegroups.com">news:1161755334.468452.170750@m7g2000cwm.googlegroups.com...


Oh yeah! Me too. I would love to hook up a version of Alex's invention
to my //c. It would take some hacking ... so hardware hackers, please
hop to it! ;-)



That's my next project. The idea is very simple: nibbles are read from SD
card
to the AVR's memory. Just like they are now. The control is a bit different:
instead of the
Apple bus interface I use the Disk ][ control signals to seek to the right
"track".
Then bits are shifted out every 4 uS. Even if no 40 uS bytes are simulated,
the
WOZ machine will still lock after a little while.

The only problem is that there is not enough internal RAM to hold the whole
track.
It taked a few millisec to re-read a "sector" from the SD card. I'm not sure
sending that
many zeros will make the Apple very happy. So I probably need to either use
extarnal
RAM or a bigger microcontroller.
Atmel's ARM7 (AT91SAM7S32) is a perfect candidate. A bit of an overkill - 32
bit
50 MIPS - but it's cheap enough. Unfortunately doesn't come in a case that
is
easy to solder.


FWIW, the controller is perfectly happy to wait for bits, so that isn't
a killer.  There are places where code looks for changing data to see
if the "disk" is still spinning, so you might want to alternate $00 with
$FF, or something.

Of course, more RAM is *always* nice.  ;-)

-michael

NadaNet networking for Apple II computers!
Home page:  http://members.aol.com/MJMahon/

"The wastebasket is our most important design
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