Image Map Image Map
Page 3 of 3 FirstFirst 123
Results 21 to 28 of 28

Thread: How to adjust the speed of an 8088-2 CPU?

  1. #21

    Default

    Quote Originally Posted by T-Squared View Post
    You know, I may have found my problems. Would bad RAM cause the discrepancies found in the demo?

    In fact, both 8088MPH (Look at the text) and Space Quest had some cut-out portions in the graphics:

    Attachment 64032

    and several programs would either not start, or cause the system to hang, despite their size being able to fit within the 256 KB of memory.

    RAMTEST even found a bad chip in one of the memory banks of the processor board I'm using at the moment.
    That is how the text on that screen is supposed to look (it's text mode so the large font isn't pixel-perfect). The skipped effects in 8088MPH are just because you don't have enough RAM - some of them require 640kB. If the RAM is present but bad, the demo will at least attempt to run those effects but might glitch or crash.

  2. #22
    Join Date
    Aug 2006
    Location
    Chicagoland, Illinois, USA
    Posts
    6,884
    Blog Entries
    1

    Default

    Quote Originally Posted by T-Squared View Post
    Furthermore, the Landmark benchmark shows a CPU speed of 7.995MHz.
    Landmark is garbage. Use MIPS.COM, or TOPBENCH.

    8088 MPH requires 512K RAM to execute properly, so until you add more RAM to your SBC-755, you can't watch the entire demo. That's why some parts were skipped.
    Offering a bounty for:
    - A working Sanyo MBC-775 or Logabax 1600
    - Music Construction Set, IBM Music Feature edition (has red sticker on front stating IBM Music Feature)

  3. #23

    Default

    Quote Originally Posted by T-Squared View Post
    You know, I may have found my problems. Would bad RAM cause the discrepancies found in the demo?

    In fact, both 8088MPH (Look at the text) and Space Quest had some cut-out portions in the graphics:

    Attachment 64032
    Okay, that looks like a consequence of the MBC-775's text mode font being a bit different from that of the IBM CGA. Which is something I already mentioned, so I should've connected the dots there.

    There's a bit of a visual explanation in my old blog post: https://int10h.org/blog/2015/08/8088...aphy_from_hell.

    The 256/1024-color portions of the demo also exploit the text mode charset, to generate the extended set of artifact colors; but those parts only depend on two specific characters, and in your earlier shots they look close enough already. So I still believe you may get a better match by setting "CGA model" to "new" - your RAM may not be enough for the entire demo to run, but at least the parts that do run may look better.

    Either way, a bad RAM chip isn't the culprit in this particular case, but Space Quest may be a different story.
    int10h.org :: :: :: blog

  4. #24
    Join Date
    Jan 2007
    Location
    Pacific Northwest, USA
    Posts
    35,365
    Blog Entries
    18

    Default

    Quote Originally Posted by Trixter View Post
    Landmark is garbage. Use MIPS.COM, or TOPBENCH.

    8088 MPH requires 512K RAM to execute properly, so until you add more RAM to your SBC-755, you can't watch the entire demo. That's why some parts were skipped.
    The 775 "turbo" speed is 8.00 MHz per the manual. Offhand, I'd call 7.995 pretty darned close. Landmark is still very useful on 8088 systems. Later CPUs, not so much. As I've said above, if you really want to know what clock rate is being used for a CPU, use a 'scope.

  5. #25
    Join Date
    May 2011
    Location
    San Antonio, TX
    Posts
    371

    Default

    Quote Originally Posted by reenigne View Post
    That is how the text on that screen is supposed to look (it's text mode so the large font isn't pixel-perfect). The skipped effects in 8088MPH are just because you don't have enough RAM - some of them require 640kB. If the RAM is present but bad, the demo will at least attempt to run those effects but might glitch or crash.
    Not according to this guy:

    https://youtu.be/0QiS2o2UaH0?t=146

    I think the bad RAM chip that I found may be responsible for skipping the effects. (Like the system can't see past the bad chip)
    Last edited by T-Squared; October 11th, 2020 at 09:45 AM.

  6. #26
    Join Date
    May 2011
    Location
    Outer Mongolia
    Posts
    3,068

    Default

    Quote Originally Posted by T-Squared View Post
    Not according to this guy:

    https://youtu.be/0QiS2o2UaH0?t=146

    I think the bad RAM chip that I found may be responsible.
    Just FYI, so far as I’m aware both Trixter and reenigne actually helped write 8088MPH. Random YouTube guy may not be as authoritative source of information.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  7. #27

    Default

    Yea um, Trixter has a valid say in this. lol.
    IBM PS/2 Model 25, NEC V30 8MHz, 640KB RAM, ATI VGA Wonder XL, 2GB SSD, Ethernet, DR DOS 6/GeOS, Xircom PE3 Ethernet

  8. #28
    Join Date
    May 2011
    Location
    Outer Mongolia
    Posts
    3,068

    Default

    ... also, ironically, in that video if you stick to the end he acknowledges it skipped a couple portions on his 256k machine.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •