Date : Tue, 19 Jul 2011 07:05:03 +0200
From : rick@... (Rick Murray)
Subject: GoMMC as a harddisc?
On 19/07/2011 01:21, Alan Williams wrote:
> So far I have not installed my GoMMC as I would have to loose my ROM/RAM
> board to fit it all in.
I wonder if a future revision of JK's GoSD could use microSDs? I figure
if it is possible to get a smaller version of the programmable logic
chip (perhaps one with bead-contacts underneath, directly fitted to the
board), it might in fact be possible to design the device barely larger
than an EPROM?
> So I am designing a new ROM/RAM board which will plug in the MOS slot
> and extend to the left.
That seems logical. I wondered why it was all too common to obscure the
ROM sockets with plug-in boards...
> It will have a RAM chip giving 4xSRAM spots and a 29F010 giving 8 ROMs.
Oh, now *that* sounds interesting.
> The prototype hasn't quite made it to the PCB fab facility yet (AKA
> kitchen table late at night :-)
;-) It's been a long time since I tried making my own boards. Mid-'80s.
Maplin used to sell (they might still?) this dinky kit with two sealed
bags of fluid. You would take a plain coppered board and *draw* on it
with a special pen. This would go into the bag with the gloopy smelly
stuff and be sealed in. You'd gently agitate the bag (I think it worked
better when it was slightly warm) for so long, then you'd take the board
out and pop it into the other bag for a while. Then finally you'd wash
the board with normal water for a loooong time.
Drawing circuits wasn't that hard (though the most complex thing was the
odd 4000 series chip). Etching wasn't that hard.
The killer was drilling all those itty-bitty holes. I had a tiny red
plastic hand drill that was like hold the end and turn the handle.
Hang on... <clicky> OMG, they still stock it!
http://www.maplin.co.uk/miniature-hand-drill-219907
> set, though I don't see anybody else having done the flash rom stuff
> yet. It doesn't seem particularly hard.
I think the programming code won't be too problematic, it seems to be a
case of:
kick Flash into program mode
erase it (poll-loop until it has completed)
write it
I don't foresee problems with writing it in 16K chunks, so we could load
up an EPROM image in memory (perhaps buffer in an SRAM slot?) and then
write it to Flash, repeat until done. It seems the main thing is not to
cut corners with the timing (unlike a lot of EPROM programming!).
The only complication is the Flash chip cells are *not* 8K or 16K. It's
more likely a 64K or 128K cell, so erasing means a complete erasure.
Still, it shouldn't be too hard to write a program to erase and
reprogram provided all the required images can be loaded. After all,
Flash cells are rated something like 100,000 writes, so no worries here!
To put it in context, you could reprogram your Flash once every fifteen
minutes for 10-12 hours a day (so time for eating and sleeping) and it
would take you 5-6 years to burn it out. Frankly, you're more likely to
burn out first...
> How is your 6502 assembler, mine is rusty as hell.
I'm doing some new ARM code stuff on my site and I've realised I've
forgotten some really basic stuff - I was pulling my hair out over MOV
crashing, and STR failing, until I remembered ADR. Gah! I really slapped
myself for that.
Why am I talking ARM code? To avoid the question, basically. I think my
6502 code will be pretty rusty too, but at least it's a simpler
processor to figure out [like, if I have to relearn bits of it]. ;-)
> Send me your postal address
Will PM.
> haven't done the lay out for that yet so it may not be for a couple of
> months.
T'is okay. My next big project is to DIY a JTAG and attempt to bit-bash
some life into a "dead" ARM-based PVR. I think faulty firmware update,
well, I *hope* faulty firmware update...
Best wishes,
Rick.
--
Rick Murray, eeePC901 & ADSL WiFI'd into it, all ETLAs!
BBC B: DNFS, 2 x 5.25" floppies, EPROM prog, Acorn TTX
E01S FileStore, A3000/A5000/RiscPC/various PCs/blahblah...