[Coco] Coco Digest, Vol 42, Issue 51
farna at att.net
farna at att.net
Sun Jan 28 21:10:35 EST 2007
Wordpad edited message...
The conventional wisdom is that it's infeasible for hobbyists to develop
their own PCI cards. But how difficult would it really be in comparison
to things we're already suggesting. I'm not suggesting hand-building
our own PC boards, but just designing the simplest possible PCI card
with nothing but the bus interface logic and a big flash ROM. The ISA
version of this would be easy enough that even I could do it (probably
even make my own PCB.) So if we're talking about an emulator running in
FreeDOS booting from ROM on an "older" system (one that still has at
least 1 ISA slot) it could be done quite easily. Switch on your PC, you
get a Power On Self-Test, and it loads up the CoCo emulator in an
instant. Put a Gig of CF on the IDE bus and you can do away with noisy
hard drives. Dig out an old packet driver for an ne2000 or 3Com
Etherlink or whatever, and add PC-LANMAN (or whatever) and you've got
some kind of rudimentary network support. So, if you don't have USB
support in DOS, you can share a USB drive over the network from another
PC. Not a half-bad way to use up that old P-III while you save for an
Hmmm... this has merit. But it would be better to go ahead and design
two different cards, or rather just a card for the PC based model. The FPGA
base really wouldn't need a PC chassis. The people most interested in
the FPGA "version" are more interested in a personality card for (a)
specific development board(s) or a complete stand-alone baord in its
The only real problem is finding a board with ISA slots. They haven't been
made in quite a while. It wouldn't be long before we were right back into
total obsolescence. Not that a CC5 wouldn't more or less be obsolete
from inception, but I wouldn't want to do all that work to saddle with something
already hard to find. If it can be done with a PCI card it would be worthwhile.
Those aren't going to be around to much longer, what with pci-e becoming
the latest standard, but they will be on MBs for a few years yet, and it will
take a lot longer for sources of used boards to dry up.
FRANK'S ORIGINAL COMMENT:
> This wouldn't just be an emulator, it would be an
> integrated software approach to a "CoCo 5" that would also have
> enhanced features. I'd like to see features from Art Flexer's ADOS3 as
> well as BASIC support for larger amounts of memory, ala "512BASIC".
> The CoCo was fun to program on in BASIC! It was easy to learn, and
> easy to write little cutsom programs for specific tasks.
But really that's just CoCo emulator + ADOS3, which is quite available
already. But I guess you're talking about a custom distribution that
would have all this stuff pre-packaged.
Exactly! It wouldn't be the existing emulator either, but a version that was
CC3 compatible with all the enhancements. I just mentioned ADOS3 and
512BASIC as examples of some of the enhancements I'd like to see, not
using them specifically. ADOS3 had to be customized for each individual's
system, it wasn't a plug-n-play solution. Lots of drawbacks to using 512BASIC
also -- there was no executable that program writers could include free,
everyone who wanted to use a program written with it had to buy their
own copy. That's why it never took off.
The problem with using the parallel port in order to get away from
custom external hardware is that you often will still need to add
external hardware. For instance, if you wanted to be able to read a
CoCo game cart over the parallel port you would have to at least put
address latches on a board with an edge connector. You'd need to output
the 16-bit address in two separate bytes, assert a R/W signal, (and
probably also E clock?) and then latch the data byte, and finally read
it over the parallel port. By the time you've gone to all that effort,
you might as well just design a "geek port" as an ISA card.
Doh!! I forgot about the CC buss having 16 ports!! It's an 8-bit, right? ;>
But how necessary is it to read a ROM pak? Most of the old paks are
on CD or in virtual disk files all over the web now. I was just thinking
about a way to access the outside. The limiting factor would be the
8 bits of the Centronics port though. That's enough for most experimenters,
though some would surely want more. Then custom cards can be built,
so it's not a huge problem. Send serial data to a PIC controller board,
it controls the relays or whatever directly. A PIC chip could be
programmed to do the data conversion from a ROM-Pak as well,
but again, how necessary is this? I think a cartridge port is a legacy
item that can be scrubbed as not practical to do, and no longer
(description of a combined emulator/FPGA board)
As I stated above, the FPGA board would be better as a total stand-alone
board not saddled with a PC.
I think that's all I really need to comment on.
So it looks like two camps now: emulation on PC based hardware, and FPGA.
I looked at the MSX "one-chip" computer (http://www.bazix.nl/onechipmsx.html).
That's what James (jdaggett) and Mark McDougal want -- except as a CoCo.
I'd build in an IDE controller as well instead of two cartridge ports.
No need for a floppy drive, as discussed above. A built in SD card slot
would be nice, but a CF card reader could be put on the IDE interface.
It's a nice design for a single board, and the specs for the later MSX2
computers compare favorably with the CC3 plus a few of the now available
upgrades. Not quite as much as I'd like to see in a CC5, but close enough.
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