[Coco] Coco Digest, Vol 42, Issue 51

[Joel Ewy]

farna at att.net wrote:
> Wordpad edited message...
>
> JOEL >
> 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
> FPGA.  :)
>
> FRANK > 
> 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
> own right. 
>
>   
Oh, I'm not really suggesting that the FPGA board would have to be in a
PC chassis.  I'm just trying to think of ways to economize on design and
production.  If there needs to be any extra hardware, it would make
sense to share it as much as possible.  So I was thinking of a single
board that could be used in different configurations as an expansion
board for a PC that gave some CoCo legacy hardware connectivity as an
option for emulators, or as a CoCo personality board for an FPGA.  As a
bonus, it might provide a way for a PC to boot directly into CoCo-land
just as fast as a CPU can read from ROM.
> 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. 
>
>   
I'm right with you there, that's why I started off musing about PCI. 
But if, as you say, an old PII, PIII, or Athlon Thunderbird system can
be a competent CoCo, then who cares whether ISA is obsolete.  So are
those systems, and there are piles of them, heaps of them lying around
for FREE, I tell you!  But I don't have any special need to see the
extra hardware hooked up to a PC.  Just an idea.
> ...
> JOEL:
> 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.
>
> FRANK: 
> Doh!! I forgot about the CC buss having 16 ports!! It's an 8-bit, right? ;>
>   
It has 8 data lines, 16 address lines, and a number of other clock and
control lines.  You gotta give out that address before you can get any
data back.  And there's a little timing that goes on as well.
> 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
> really necessary. 
>
>   
I think you're right when you're talking about the emulator --
especially if you also have a real CoCo lying around and some reasonably
convenient way to transfer data between them.  But I have to say, I
still find something appealing about the idea of (certain kinds of)
software on ROM paks.  I guess the closest thing to that now is the
Portable Apps Suite on a USB mem stick.  And I do think that any FPGA
CC-Five worth its weight in silicon needs a CoCo cartridge port.  If
it's going to really replace a CoCo for me, I gotta be able to plug in
my CoCo stuff.  And the very idea of a simple bus interface that the CPU
can access directly for exactly the kinds of experimentation you mention
above is one of the very reasons somebody might use a CoCo-like system
today instead of a new-fangled, overly-complex PC.
> JOEL:
> (description of a combined emulator/FPGA board)
>
> FRANK:
> As I stated above, the FPGA board would be better as a total stand-alone
> board not saddled with a PC. 
>
>   
That's not really what I had in mind either.
> ...
>
> 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. 
>
>   
I think you would just have an IDE interface for mass-storage, be it CF
or an electro-mechanical hard drive, and possibly an SPI interface that
can be used for SD/MMC.  Treat the latter as your removable medium in
place of floppy disks.  But as I mentioned above, I do think that the
CoCo bus needs to be brought out.  So one could plug in an old floppy
controller if the need arose.

JCE
> --
> Frank Swygert
> Publisher, "American Motors Cars" 
> Magazine (AMC)
> For all AMC enthusiasts
> http://farna.home.att.net/AIM.html
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>
>