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Thread: Lo-tech XT-CFv3 versus Texelec's "Lo-tech ISA XT CF Adapter rev. 3"

  1. #31
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    All that, but the V20 support in the XUB means it performs a REP INSB which is also a contributing factor.
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  2. #32
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    Quote Originally Posted by Trixter View Post
    All that, but the V20 support in the XUB means it performs a REP INSB which is also a contributing factor.
    Of course. I was just sort of surprised that it seems like that REP INSB may well be about a tie for DMA even on the slowest possible clock rate you'd be likely to be running 186-enabled XUB on.

    There might be some not-as-readily-benchmarked advantage to using DMA if it actually allowed some "multitasking" between disk transfer and the CPU, I guess. And of course not everyone's going to want to swap their 8088.

    Has anyone made a version of the XT-CF for ISA bus machines that uses the jrIDE memory mapped I/O method?
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  3. #33
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    Hey Legacysystem please check PM
    *FrankG*

  4. #34

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    So, I'm better late to the party than never I suppose.

    Re open source: Originally the intention was to provide all Lo-tech stuff completely open, however, a load of clones soon appeared - some still available - with really, really poor quality and no support from the seller. This created a real problem with either telling people sorry I can't help, or absorbing large amounts of time - and in some cases money, shipping parts - to end-users who themselves were not at fault. And of course undermined trust in the products. As life so often does, twists and turns left me needing someone to make these, and TexElec did and still does make really good quality boards and I thoroughly recommend his products to anyone. This has made it possible to continue to supply these incredibly low-volume parts that would otherwise have dried up years ago. By publishing the schematics (and hosting the XTIDE Universal BIOS SVN) I do hope that this balance is about right.

    re DMA. The DMA on XT-CFv3 (CPLD powered) transfers one byte for every ISA bus cycle. Obviously there is some overhead configuring the controller, but that is why it is faster than memory-mapped. The latter must read a byte from location 1 and write it to location 2 via the CPU, and repeat. So memory-mapped is the same speed as port-mapped IO, on a V20 that has rep insw available. With DMA a stream of data is pumped out the card and saved directly to memory. The board can deliver 530KB/s on an XT with a CF card that supports multi-sector transfers. Which is obviously a bit silly. There is no multi-tasking benefit though as the CPU is put in a wait-state whilst the transfer is happening, which is why we can introduce distortion on a SoundBlaster with it. There are no safeguards or checks or balances with ISA. Everything else stops until the DMA is done.

    However, as said the CPLDs are no longer available and they also proved to be unreliable. I'd be interested to know if @Trixter's card still works, as all prototypes eventually died as far as I'm aware.

    To the OP's point, anyone wanting a single-slot ISA/CF adapter might consider the XT-CF-v2, which is available via Texelec here.

    Hope that helps and sorry for the multi-year delay in replying!
    Last edited by pearce_jj; January 26th, 2021 at 10:04 AM.

  5. #35
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    James, my XTCF prototype (if that's the one that you sent me) still works fine, the last I checked.

  6. #36
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    I believe mine works as well (and is my most prized homebrew card, it exceeds the speed of my fastest 8-bit SCSI adapter). I will pull out the system where I have it permanently installed and test later this week and confirm.

    In terms of component failure, I once ran the card for nearly 48 hours straight playing two feature-length movies off of it at a VCF Midwest show, so that was a fairly substantial burn-in test.

    I would love to see DMA revisited in an XT-IDE design. Speeds in excess of 300KB/s may seem "silly" but they really make 808x systems feel snappy (for example, Microsoft Word loads in under 2 seconds when paired with a CF card, vs. 10+ seconds with a traditional hard disk subsystem). While CPLDs are no longer available, are FPGAs viable? Or some other design?
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  7. #37
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    Lattice still makes (and Mouser still sells) the Lattice 5V (e.g. M4A5-xxxx) CPLDs. Mostly TQFP, but there are some PLCC holdouts there. I don't think any 5V FPGAs still exist.

    I know that James knows about the Atmel/Microchip ATFxxxx stuff--I believe that's what he used originally.

  8. #38

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    Thanks for the replies. Glad to hear these boards are still working.

    So I think we're saying we'd like another board supporting CompactFlash with DMA support that can be readily assembled by hobbiests.

  9. #39
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    I would certainly be in support of that, for obvious reasons. I cannot advise on such a project due to limited understanding of electronics/hardware, but from a customer standpoint, I would be willing to spend $100 per adapter, and I would be willing to assemble myself but would greatly prefer no surface-mount components I'd need to solder (but that's not a deal-breaker, just a nice-to-have).
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  10. #40
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    Very much agreed. I don’t think that CF has to be the only media type, if something else is easier, though. SD/uSD cards are definitely available rather cheaply, as are m.2 SATA SSDs. Personally, I have been using m.2 SATA SSDs with 44pin-to-m.2 PCBs and 44-40pin adapters, in quite a number of my vintage machines.

    - Alex

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