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Thread: Score!!!

  1. #1

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    Now construction of the 1Mb RAM + XT-IDE + 8255 card can begin! =:3


    They're a little too long for my PS/2 Model 25 though.......... The band saw will fix that, though!



    The thing only has 2 ISA slots, and it's somewhat annoying to have a ribbon cable with an external backplane hanging out of it. One slot has to contain an Ad Lib card, so I really only have one slot available.


    So the idea is to combine the RAM expansion and hard drive interface onto one card, and also interface to a Raspberry Pi GPIO header via an 8255. An analog switch chip or two and a solid state relay will allow the contraption to switch the built-in CRT between the Model 25's video and the rPi, as well as allow the PS/2 to power the Pi up and down. On the DOS side, I'll hack up a program to make the 8255 power up the Pi and switch the video over to it. Once the Pi is booted, the program running on DOS will read keyboard and mouse events and transfer to them to the Pi through the 8255. A daemon running on the Pi will then inject those events into the Linux kernel, as if they were being generated by actually-connected input peripherals. A more advanced project would be writing a userspace filesystem driver to let the Pi access the PS/2's disk drives, but that is awfully complicated and something to do Later(tm). A DOS packet-driver bridged to the Pi could also be a possibility.


    This will allow me to have a vintage Model 25 that's really a Model 25, not just a shell with a modern system hidden in it. I can play DOS games on the real hardware, at least the ones it supports. But when I want to play 386 protected mode stuff, Amiga stuff, or whatever, I'll be able to execute a command to fire up the Pi and do stuff under emulation that the PS/2 could never do on its own.


    I know, it's kind of a silly and backwards idea, but I think it will be interesting. :3 .... As soon as I manage to finish some other projects and get started on it, haha.


    I 'spect an aux power supply for the Pi will have to go somewhere, too.... Probably plug in through the card bracket or something, and then power the Pi over the GPIO header, even though there's no fuse in-line that way.
    -- Lee

    May Be Interested In Acquiring: Commodore PC(286+), any PC-era Tandy stuff, Peculiar Old Serial Terminals (TRS-80 DT-1 in particular), TRS-80 Model 4

    Old Computer Fun YouTube Channel!

  2. #2

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    Quote Originally Posted by bladamson View Post
    The thing only has 2 ISA slots...
    Have you thought about using a larger riser card, i.e., one with more slots?
    PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

  3. #3

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    Quote Originally Posted by Stone View Post
    Have you thought about using a larger riser card, i.e., one with more slots?
    The planar won't fit into the case if a taller one is used. The Model 30 has a 3-slot one that will fit, but it's too tall to let the thing close. Pictures there are with the planar pulled out of the rest of the machine.

    I've used a ribbon cable leading out to an external passive backplane in the past, but that's electrically noisy and annoying to move.
    -- Lee

    May Be Interested In Acquiring: Commodore PC(286+), any PC-era Tandy stuff, Peculiar Old Serial Terminals (TRS-80 DT-1 in particular), TRS-80 Model 4

    Old Computer Fun YouTube Channel!

  4. #4
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    The Model 25 is a comparatively very compact beast. Not much clearance at all when the machine's closed up.

  5. #5

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    Here is it reassembled, so you can see what I mean. They're an all-in-one unit, intended to compete with the original Macintoshes.

    IMG_20191026_174403.jpg
    -- Lee

    May Be Interested In Acquiring: Commodore PC(286+), any PC-era Tandy stuff, Peculiar Old Serial Terminals (TRS-80 DT-1 in particular), TRS-80 Model 4

    Old Computer Fun YouTube Channel!

  6. #6
    Join Date
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    I've got a blank, unused FR4 16-bit ISA prototype card that's quite a bit shorter (maybe 2/3 length). I'll trade,

    Alternatively, check these guys out Both short XT and AT protoboards.

  7. #7

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    I've passed over several of the shorter ones, as I didn't think I'd be able to fit all the stuff I want on them. Those Vector boards are usually $60 a pop and only available by special order, but three of them came up on ebay for $25/each so I bought all he had. :3

    These look to be old stock, and there is some oxidation on the brackets. But a quick trip to the bench wheel and some paint ought to fix them right up.
    -- Lee

    May Be Interested In Acquiring: Commodore PC(286+), any PC-era Tandy stuff, Peculiar Old Serial Terminals (TRS-80 DT-1 in particular), TRS-80 Model 4

    Old Computer Fun YouTube Channel!

  8. #8

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    Vetco! I know that name!

    EDIT: I'm a doofus, those bags said vector, not Vetco.

    Happened by their store when visiting Seattle for the Living Computer Museum. Neat place. They had some similar boards just on a shelf at the end of an aisle, but with wire-wrap sockets instead of just perfboard. Bought one of the full-length ones for $15.
    Also, if you ever get an ethernet solution working, check out EtherDFS. Basically you can access a partition on the Pi as if it were a hard drive (C, D, etc). Makes a great file-transfer solution.
    Last edited by Nevets01; October 28th, 2019 at 08:04 PM.
    Current favorites: IBM 5160 (EGA+Hercules+PGC, 4 floppies, XT-IDE), Compaq Portable ii (replaced PSU and keyboard, EMS card), ASR 33 Teletype (now FULLY armed and operational!)
    Wishlist: IBM 5161 (expansion chassis), IBM 5175 (monitor for PGC), IBM 3270 PC keyboard card, DG Nova IO controller, and the meaning of life.

  9. #9

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    Quote Originally Posted by Nevets01 View Post
    Also, if you ever get an ethernet solution working, check out EtherDFS. Basically you can access a partition on the Pi as if it were a hard drive (C, D, etc). Makes a great file-transfer solution.
    Ahhh nice. That looks a lot more DOS-compatible than NFS.

    I want to go the other way too, though, with the pi able to get at the PS/2's drives. I *think* I can do this with a daemon that interacts with a program running on the 8086 to read sectors, then talks the NBD protocol over a Unix socket, and get them mounted under Linux that way. Unless there is an easier way to make the daemon look like a random-access "file" to other programs (then presumably I could make DOSBox mount it as a "disk image", or mount it on the loopback device, or something). Handling floppy changes will be troublesome, though. Have to turn off any read caching and mount synchronously I 'spect. But that's all a project for way later, once the hardware is actually working. =:O

    Edit: I'd forgotten about FUSE. That might be easier than trying to use NBD.
    -- Lee

    May Be Interested In Acquiring: Commodore PC(286+), any PC-era Tandy stuff, Peculiar Old Serial Terminals (TRS-80 DT-1 in particular), TRS-80 Model 4

    Old Computer Fun YouTube Channel!

  10. #10

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    Having the DOS machine export a disk as NBD over TCP/IP might be the easiest way to implement. But keep in mind that the DOS machine must not access its own disk while the connection is active (including TSRs), because the file system will be in some intermediate state while mounted. Better to enforce a SCANDISK after disconnect.

    If you want to use file-based access, I'd probably aim for an FTP server (mTCP has one) and use some FTP-based FUSE driver (e.g. curlftpfs) on the other end. No development required for this one.

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