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Thread: ISA card with 8086, 8078 and 80286 for Olivetti M24, what the hell...

  1. #11
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    Here is something similar, but without additional 8086 and link to it's processor socket on the mainboard: https://retrocmp.de/hardware/pc-elev...evator-286.htm

  2. #12
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    The PC-elevATor is one of the rarer boards that was a complete 286-on-a-card; when you enable acceleration, the entire system runs off the card. That's why it doesn't need a ribbon cable to the CPU socket on the mainboard.
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  3. #13
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    How does that card work, switching from 808x to 80286? And it looks like it can return back to 808x...?

  4. #14
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    If memory serves, you run UP.COM to boot the board and switch to it, then DOWN.COM if you want to come back "down" to the 8088. The 8088 continues running, but IIRC the 286 board reboots every time you run UP.COM to switch to it. LEVEL.COM shows which environment you're in, IIRC.
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  5. #15

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    A similar board by Orchid could, if I remember correctly, hot-switch between the 286 and 8088 (mid-application on both) by pressing a given key-combination on the keyboard. It's been years since I went through the documentation for it, so I'll have to double-check.

    In any case, the handshaking between the two was done using a DOS driver. In Orchid's case, the driver is really picky about the version of DOS used.

  6. #16
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    I thought the hot-switch was a low/high speed of the accelerated CPU, not a switch between CPUs, but I could be wrong.

    One of the more interesting accelerators I have is an 8086 accelerator for the 8088. How is this any faster? It comes with 8k L2 cache. The advertising claims 3x speed improvement, which would put it into 286 territory, but I haven't had a chance to benchmark it yet.
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  7. #17
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    I am kind of curious how that "PC Elevator" card puts the main CPU to sleep so it can drive the data/address bus when it's in command, given it doesn't run a cable to the CPU socket. Maybe it flagrantly abuses a DMA channel? That or it keeps the host CPU running as an I/O processor? (But it seems like it would at the very least still need to use DMA to update the video card.) Can it access any RAM on the motherboard, or when it's in 286 mode does it run entirely from its onboard RAM? (Holding down a DMA line constantly could potentially mess with RAM refresh. And how does it handle interrupts?)
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  8. #18
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    Why would DMA be necessary to update the video card?

    I don't know the answers offhand, but this may help: https://retrocmp.de/hardware/pc-elev...evator-286.htm
    In particular, he has extracted a portion of PC Magazine that covers the cards: https://retrocmp.de/hardware/pc-elev...1986-09-16.pdf
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  9. #19
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    Quote Originally Posted by Trixter View Post
    Why would DMA be necessary to update the video card?
    My thought there is so far as I know the DMA lines are the only method on the ISA bus to tell the onboard CPU to stop being the busmaster and let another device drive the address and data lines. (short little blurb on ISA bus mastering.) Digging through that full PDF seems to confirm that's what they're doing; from page 131:

    The large-size boards generally use their own memory and may not even require removing the 8088 from its socket. We tested Earth Computers TurboAccel-286, Microway Number Smasher/ECM, Classic Technology 286 SpeedPak, Orchid PC Turbo-286e, and the Applied Reasoning PC-elevATor. These boards disable your system board 8088 through a DMA channel and take over your whole system...
    If there isn't another method to halt the onboard CPU then the only way I could see for one of these boards to access the video card would be to update a dual-ported buffer in its own RAM and use a routine running on the onboard CPU to copy any updates over. (Otherwise you'll have the onboard CPU sitting there generating bus cycles as it cools its heels running NOPs or whatever the driver software has it doing, which will also be driving the address and data lines on the ISA bus.)

    Still also wondering how they handle interrupts. I assume they run a handler on the main CPU (that works as long as they're not using a DRQ to keep it quiet?) instead of trying to probe them directly off the ISA bus wires.
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