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Thread: Tandy 1000 A/EX/HX DMA speed-up

  1. #31
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    Quote Originally Posted by Trixter View Post
    Not to derail the conversation too much, but I'm publishing a video this weekend that proves the Tandy 1000 (the original) can be just a hair slower than the IBM PC, found when doing a software-controlled sound output test. The program in question used software loops for timing, and a lot of port 61h writes. The audio is audibly slower/lower in pitch than when run on the IBM PC. I'm unable to account for this discrepancy.
    Does your T1000 have a RAM card installed or is this part of a demo meant to run on an un-expanded machine? RAM access to the shared planar RAM probably is slower than a PC; faster than a PCjr but from reading the manual I don't think it's contention-less.

    If you want a data point I'd be willing to run your software loop on my SRAM EX in slow mode, but maybe that won't tell you anything useful. (especially since I have a V-20.)

  2. #32
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    Quote Originally Posted by eeguru View Post
    Most plausible theory is the 1000 did share video RAM in much the same way as the Jr. However I suspect the extra CPU waits due to the video access were more efficient than the Jr's video gate array as the 1000 was an evolution. And obviously the 1000 mapped video RAM at the end of main memory so there wasn't the nasty hole.
    A good theory, however the PCjr's slowdown at very high interrupt rates (16 KHz) is much worse than on a Tandy 1000. So the Tandy 1000 is slower, but only by 1%, just enough to be audible. On an expanded PCjr, where the main code runs out of the expansion but the interrupt is reading 4 bytes from the first 128K at 16 KHz, it's much more pronounced.
    Offering a bounty for:
    - The software "Overhead Express" (doesn't have to be original, can be a copy)
    - A working Sanyo MBC-775, Olivetti M24, or Logabax 1600
    - Music Construction Set, IBM Music Feature edition (has red sticker on front stating IBM Music Feature)

  3. #33
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    Quote Originally Posted by Trixter View Post
    A good theory, however the PCjr's slowdown at very high interrupt rates (16 KHz) is much worse than on a Tandy 1000. So the Tandy 1000 is slower, but only by 1%, just enough to be audible. On an expanded PCjr, where the main code runs out of the expansion but the interrupt is reading 4 bytes from the first 128K at 16 KHz, it's much more pronounced.
    Paging through my copy of the DATABASE.INI for Topbench it doesn't look like there are results for an original 1000/1000A in there, the closest thing there is is a 1000 SX in slow mode. And comparing the scores for that to the scores UnknownK placed in the thread earlier suggests the original 1000 may *be* slower, slightly, than later models. 1000SX from database.ini:

    [UID989015B1]
    MemoryTest=3742
    OpcodeTest=1770
    VidramTest=2082
    MemEATest=1962
    3DGameTest=1883
    Score=4
    CPU=Intel 8088
    CPUspeed=4.77 MHz
    BIOSinfo=
    BIOSdate=19860714
    BIOSCRC16=9890
    VideoSystem=CGA
    VideoAdapter=Tandy 1000
    Machine=Tandy 1000 SX (4.77MHz)
    Description=
    Submitter=Great Hierophant

    UnknownK's score from a 1985 Tandy 1000 with a DMA memory card installed:

    [UID85086DB6]
    MemoryTest=3823
    OpcodeTest=1833
    VidramTest=2148
    MemEATest=2028
    3DGameTest=1922
    Score=4
    CPU=Intel 8088
    CPUspeed=4.77 MHz
    BIOSinfo=unknown
    MachineModel=0000
    BIOSdate=19850305
    BIOSCRC16=8508
    VideoSystem=CGA
    VideoAdapter=Tandy 1000
    Machine=Tandy 1000

    It's not a lot but it's measurably slower in every test, which is a little odd since you'd think they should be equivalent. The SX score is almost dead on with a 5150 from the database. Perhaps an original 1000 actually *is* slower. Do you have another 8088 model (EX/HX/SX) to run your test on?

    As an aside, I noticed right under the 1000SX score in the database is a score from an expanded IBM PCjr (Description=IBM PCjr running in the faster RAM of the memory expansion). The scores from that PCjr are better than the 1000SX in every category but the VidRamTest by about as much as my SRAM EX beats the DMA/DRAM HX. DMA expansions were rare for PCjr's, so... I wonder if likewise that RAM expansion doesn't burden the system with waiting for refresh cycles.

  4. #34
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    Quote Originally Posted by Eudimorphodon View Post
    I wonder if likewise that RAM expansion doesn't burden the system with waiting for refresh cycles.
    The more common IBM 128KB memory side-cars did use Dynamic RAM which would require refresh. But at least the video wasn't in contention. But even with 1, 2, or even 3 128KB side-cars, you wouldn't want to block out the entire 128KB from use by DOS unless you were specifically doing this benchmark. Each KB was $$ ($$$$ at 1980s exchange rates). I'm guessing it was something like a JR-IDE which uses SRAM and runs a hair faster than DRAM due to no refresh.
    "Good engineers keep thick authoritative books on their shelf. Not for their own reference, but to throw at people who ask stupid questions; hoping a small fragment of knowledge will osmotically transfer with each cranial impact." - Me

  5. #35
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    Also, re: how comparable the Tandy 1000's video ASIC is to the PCjr's, I think these scores:

    Quote Originally Posted by Unknown_K View Post
    ;Data collected by: TOPBENCH | Benchmark and detection stub | Version 0.97e
    ;This file contains fingerprinting information about your computer. Please
    ;email this file to trixter@oldskool.org with a subject line of "Benchmark" to
    ;help test these routines and seed the TOPBENCH database.

    [UID85086477]
    MemoryTest=4232
    OpcodeTest=2103
    VidramTest=2236
    MemEATest=2375
    3DGameTest=2152
    Score=4
    CPU=Intel 8088
    CPUspeed=4.77 MHz
    BIOSinfo=unknown
    MachineModel=0000
    BIOSdate=19850305
    BIOSCRC16=8508
    VideoSystem=CGA
    VideoAdapter=Tandy 1000
    Machine=Tandy 1000

    DOS 2.11 Boot disk, 128KB no DMA.
    Compared to these:

    [UID7F5C71D]
    MemoryTest=5926
    OpcodeTest=3584
    VidramTest=3373
    MemEATest=4392
    3DGameTest=3490
    Score=2
    CPU=Intel 8088
    CPUspeed=4.77 MHz
    BIOSinfo=COPR. IBM 1981,1983 (06/01/83, rev. 86)
    BIOSdate=19830601
    BIOSCRC16=7F5C
    VideoSystem=CGA
    VideoAdapter=IBM PCjr
    Machine=IBM PCjr
    Description=Stock, 128KB RAM. This score is accurate -- it is slower because the first 128KB of PCjr RAM is also display RAM and has an additional wait state.
    Submitter=trixter@oldskool.org

    Settle that. It doesn't look like it's completely wait-state free (and Unknown_K's scores support that with the aforementioned 10%-ish hit compared to having a RAM card installed) but it is clearly a massive improvement. (The video chip does have 16 bit access to RAM and separate video and CPU data latches, so contention would at least be substantially reduced from just that. It also looks like it may be able to generate wait states with better granularity for when conflicts do happen, although I can't say that without knowing more about how the Jr. works.)

  6. #36
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    Quote Originally Posted by eeguru View Post
    I'm guessing it was something like a JR-IDE which uses SRAM and runs a hair faster than DRAM due to no refresh.
    Yeah, that's what I was was suspecting. A Jr-IDE should be roughly the equivalent to SRAM in a Tandy for expansion RAM speed, and would be another data point for "your machine will be faster with no DMA controller unless you need it for something".

  7. #37
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    Quote Originally Posted by Eudimorphodon View Post
    Perhaps an original 1000 actually *is* slower. Do you have another 8088 model (EX/HX/SX) to run your test on?
    I do, but I'm swamped until about 1-2 weeks after VCFMW is over.
    Offering a bounty for:
    - The software "Overhead Express" (doesn't have to be original, can be a copy)
    - A working Sanyo MBC-775, Olivetti M24, or Logabax 1600
    - Music Construction Set, IBM Music Feature edition (has red sticker on front stating IBM Music Feature)

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