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Thread: Trixter's latest magic... Holy how-in-the-hell!!!???

  1. #111

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    Quote Originally Posted by Eudimorphodon View Post
    Totally ignorant comment: Isn't a fairly major bottleneck for both the 8086 and the 8088 the need to do effective address calculation using the shared ALU hardware? I *think* the hit varies depending on the addressing mode of the individual instruction being executed but my impression was that in the worser-case instances the need to do the second bus cycle on the 8088 adds only marginally to the total cost of memory operations, which means while there may be a "50% improvement" with certain types of code in a random instruction mix the improvement is going to be substantially less?
    8086 adds delay when accessing data starting on odd memory locations, which is that 50% in question.
    Current systems owned by me:
    Vintage:IBM PC/XT submodel 087 ( 1983 ), [Kon]tiki-100 rev. C (1983), Compaq Portable I ( 1984 ), IBM PC/XT submodel 078 ( 1985 ), IBM PC/XT286 ( ~1986 ), 3x Nintendo Entertainement Systems ( 1987 ).
    Obsolete:Commodore A500 ( ~1990 ), IBM PS/2 model 70/386 type 8570-161 ( 1991 ), Atari Lynx II ( ~1992 ), Generic Intel 486SX PC ( ~1993 ), AT/T Globalyst Pentium w/FDIV bug MB ( 1994 ), Compaq 486DX4 laptop ( ~1995 ).

  2. #112
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    Well, my assumption was that the code mix was in fact not 'random' (as it probably is in something like TOPBENCH), but something carefully crafted to make the most of the abilities of the 8088/8086.
    So, you would avoid unaligned accesses, and you would avoid complex instructions and slow addressing modes, and instead just plough through memory with the fastest/shortest instructions available (lods/stos/movs/xlat/push/pop are your friends).
    In that case, not only will the 8086 shave quite some time off each memory access, both for instructions and for data, but also, it has a longer prefetch buffer and more bandwidth to keep that buffer filled, so as an extra 'bonus', you might run code from the prefetch buffer more often.

    Running 'optimal' code for an 8088 on an 8086 or vice versa is not optimal, and not what I meant.
    For example, the sprite compiler in 8088 MPH is specifically written for the 8088, and it does not pay attention to alignment with word reads, since the 8088 doesn't care.
    An 8086 can read aligned words twice as fast as unaligned words, so it might make sense to access words only on aligned addresses, and emit byte-fetches to align the code here and there.
    So hypothetically I would design a different compiler for 8086 MPH.

  3. #113

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    Hi,
    first of off, VERY IMPRESSIVE for it's time.

    Second, I want to run this on my IBM 5140 with RCA Expansion. It's basically a CGA Card modified for it's expansion bus, but like all other later IBM CGA cards, it uses a different chip, and mine happens to be the HD46505RP instead of the MC6845. Somewhere on the comments of this demo, one of you guys said the code can be tweaked for the HD6845.

    Are there any minor and major differences between the HD46505RP and the HD6845?

  4. #114

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    Quote Originally Posted by Kazblox View Post
    Are there any minor and major differences between the HD46505RP and the HD6845?
    Nothing as far as I know. I think the HD46505 will be sufficiently compatible to run the final version (which is coming soon!) There is just one MC6845-specific quirk that we used in the party version (using hsync width 0 which the MC6845 interprets as width 16 but other CRTC's interpret as turning off hsync altogether). In the final version the hsync width is user configurable. Everything else we did should be compatible with other CRTCs with the possible exception of the lockstep code (but the consequences of that not working should be minor).

  5. #115
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    Quote Originally Posted by reenigne View Post
    There is just one MC6845-specific quirk that we used in the party version (using hsync width 0 which the MC6845 interprets as width 16 but other CRTC's interpret as turning off hsync altogether).
    The interesting thing is that the Motorola documentation actually seems wrong: http://www.classiccmp.org/dunfield/r/6845.pdf
    It says that value 0 means no HS is provided.
    So it looks like the clones follow the information in the datasheet.

    But the way the MC6845 actually works, makes more sense. Turning off HS seems to have no practical use. Setting the width to 16 does, however.
    The PIT does the same for example, a countdown value of 0 is interpreted as 65536.
    So in my opinion it's the clones that don't reinterpret 0 as 16 which are the quirky ones.
    Then again, they just follow Motorola's specs, unlike Motorola's own chips

  6. Default

    Okay I received my latest CGA card, which is a full length one, feature complete with CGA snow \o/



    Also, this one runs 8088MPH all the way to the end. But what about these questionable parts? Screen was rolling+flickering like crazy. Those two RCA ports didn't give any picture not even with King's Quest, so I wonder what's up with that.

    https://gabucino.hu/tmp/IMG_3891.JPG
    https://gabucino.hu/tmp/IMG_3892.JPG
    https://gabucino.hu/tmp/IMG_3893.JPG
    https://gabucino.hu/tmp/IMG_3897.JPG
    https://gabucino.hu/tmp/IMG_3898.JPG

  7. #117
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    Your card is a clone card ("Yangtech Electric Co Ltd") and has a clone 6845 chip, which is why some parts are not syncing up for you.
    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
    - Documentation and original disks for: Panasonic Sr. Partner, Zenith Z-160 series
    - Music Construction Set, IBM Music Feature edition (has red sticker on front stating IBM Music Feature)

  8. #118
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    Quote Originally Posted by Gabucino View Post
    Okay I received my latest CGA card, which is a full length one, feature complete with CGA snow \o/
    Interesting.
    I figured there'd be Taiwanese-made clones that are pretty much a 1:1 copy of the real IBM. But so far the only CGA-compatible chips I've encountered in clone PCs were made by ATi or Paradise.

    Screen was rolling+flickering like crazy.
    Yes, if you would replace the UM6845 chip with a Motorola 6845, that would fix it
    Alternatively, we can release a patch that doesn't use hsych width 0, which avoids this problem on clones.
    The Kefrens part does not look correct either (I take it you used a real 8088 CPU at 4.77 MHz?). In fact, it looks similar to what I got on the ATi and Paradise cards. For some reason they don't display any bars at the top part of the screen.
    I wonder if this is also the UM6845's doing, or if there's something else that affects that.
    The Hitachi-made HD6845 found on some real IBM CGA cards does not have this problem at least.

    Those two RCA ports didn't give any picture not even with King's Quest, so I wonder what's up with that.
    I wonder why there are two ports in the first place. Perhaps they aren't composite output, but something else?
    Looking at the circuitry though, it looks like there should be a composite circuit on there. If you look at the headers in the top-right corner, there should also be a composite signal on those. You could try tapping into that.
    On real IBM CGA cards, this is where you can attach a TV modulator. The IBM 5155 uses it to connect the internal monochrome monitor.
    The headers on this card look the same, so I suppose they also have a composite signal on there.
    Last edited by Scali; June 14th, 2015 at 04:16 AM.

  9. #119
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    Quote Originally Posted by Gabucino View Post
    Also, this one runs 8088MPH all the way to the end. But what about these questionable parts? Screen was rolling+flickering like crazy. Those two RCA ports didn't give any picture not even with King's Quest, so I wonder what's up with that.
    I've got the same monitor matched up to a EGA card on my XT clone desktop.
    Attached Images Attached Images
    Thomas Byers (DRI)- "You'll have a million people using the A> [MS-DOS prompt] forever. You'll have five million using [nongraphic] menu systems such as Topview, Concurrent PC-DOS, Desq, and those types. But there'll be 50 to 100 million using the iconic-based interfaces."

  10. #120

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    That was very-very interesting to watch. Is it even possible to bitbang more out of that hardware? Your team warped the computers physics barriers at PhD levels.

    I have a question though. On old consoles, hackers often use unused i/o registers for scratchpad memory storage + squeeze some extra cycles sometimes. Or even safely run code off the sram of a SMS cartridge. Is there any benefit / possibility to do this on a legacy pc?

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