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Thread: Project: Micro 8088 - Chipset-based 8088 XT compatible processor board

  1. #61
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    Quote Originally Posted by spark2k06 View Post
    Hi!

    I have a Micro8088 assembled and everything works fine. However, the CheckIt program gives an error on DMA channel 0. Tested with 74HC573 chips and also with 74F573. Does anyone know what the cause may be? and if it has any more involvement in the performance of the system other than the failure reported by the checkIt program?
    It works better?! The IBM PC/XT DMA implementation is horrible... Instead of using proper 8088 bus request/grant signals. DMA logic "steals" the bus from CPU by inserting wait cycles, and disconnecting the CPU from the bus. This results in all kind of "interesting" issues, such as ALE pulsing at the weird times and confusing TVGA8900/TVGA9000 based graphics cards I haven't run the bus utilization/timing analysis, but it is also possible that this implementation results in some performance degradation as well... because additional cycles inserted between disconnecting CPU from the bus, and enabling DMA (and vice versa).

    The DMA implementation in FE2010 is better. It does use RQ/GT signals. The difference in the implementation might result in slight timing differences between FE2010-based systems and the original IBM PC/XT.
    Speaking about DMA channel 0 particularly, most likely FE2010 doesn't even contain the proper 8237 logic for it, just the parts required to implement DRAM refresh. And that's probably the reason it is failing the CheckIt tests.

  2. #62

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    Thanks @nztdm and @sergey for your answer. Another question, now related to a particular game. It's about "Alleycat", a classic from the PC-XT era. The fact is that by playing game, I notice that the keyboard does not respond very well, the game slows down at times. And the most remarkable effect occurs on the screen of the fish tank, the cat can barely dive and it is impossible to complete it.

    I have a Trident TVGA9000i, with which I have performed the following tests:

    1. I use it such with Micro8088. The problem that I have explained is reproduced.

    2. I use it with Micro8088 and SVM89.EXE application, to emulate CGA. The problem of slowdown and keyboard response disappears, however, the screen is not well centered and certain graphic glitches are produced.

    3. I use it such with a Pentium II motherboard. All right and without problems.

    I have also playing the game in an emulator called pcEM, in a PCXT emulated with a Trident TVGA9000, and without problems. I have seen the game in youtube videos in original PCXTs, and without problems.

    Any ideas about it?

    Thanks!

  3. Default

    Quote Originally Posted by sergey View Post
    Speaking about DMA channel 0 particularly, most likely FE2010 doesn't even contain the proper 8237 logic for it, just the parts required to implement DRAM refresh. And that's probably the reason it is failing the CheckIt tests.
    Think so as well - just checked it on my Micro 8088 - the same error with DMA ch 0...

  4. #64

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    Hi. I want to build an 8088 board but I donít find the FE2010A chip. Anyone knows where to buy one? Thank you

  5. #65
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    Quote Originally Posted by skywalky View Post
    Hi. I want to build an 8088 board but I don’t find the FE2010A chip. Anyone knows where to buy one? Thank you
    There are a few on eBay, although they are quite pricey. You can also try getting a quote from https://www.utsource.net

  6. #66
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    Quote Originally Posted by spark2k06 View Post
    Thanks @nztdm and @sergey for your answer. Another question, now related to a particular game. It's about "Alleycat", a classic from the PC-XT era. The fact is that by playing game, I notice that the keyboard does not respond very well, the game slows down at times. And the most remarkable effect occurs on the screen of the fish tank, the cat can barely dive and it is impossible to complete it.
    I remember trying that game on my Micro 8088 system, and I don't remember having such issues. I'll try to test it again...

  7. #67

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    I have assembled my micro88 and everything is working right. I have assembled a floppy+serial card (the design of Sergey Malinov) and floppy is working right but serial port it is working erratically. Sometimes my mouse works and then pointer gets hanged.
    I have tried with a Multi IO card from a old XT, and it is working rigth.
    The jumper configuration in my card is SW1 = 01000001 and SW2=11010000
    There are any known problem? Could be a configuration issue?
    Anyone knows where could be my problem?

    thank you in advance

  8. #68

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    Difference without and with emulation via SVM89.exe on Micro8088 and Trident 9000i:


  9. #69
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    I found this 10 years old and very lengthy thread that discusses the performance differences between CGA and VGA. It specifically refers to Alley Cat - see post #11.

  10. #70

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    Try moving the serial card closer to the Micro8088. Does that help?

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