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OSSC + Pentium 233 MMX (VGA)

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This topic contains 9 replies, has 5 voices, and was last updated by  James-F 1 month, 3 weeks ago.

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  • #19339

    James-F
    Participant

    In case anyone wonders how the OSSC handles a retro PC with VGA only output…
    I’m in tears of joy, god bless you marqs.

    It does 640×400 (native DOS and 99.999% games) and 640×480 marvelously!!!
    640×400 runs in 384p Line2x mode but I adjusted V.Active to 480 so my screen shows it in 4:3 (1280×864),,,
    In 384p (640×400) Line2x mode the result is super sharp and smooth 70Hz, just like a quality PC CRT from back then would but on a modern LCD with HDMI.
    Yes, the screen has VGA input but the OSSC looks MUCH sharper in Line2x mode, as it would on a CRT.

    Did I say the OSSC is great already? 🙂

    Pentium 233 mmx
    ossc
    NC
    doom full
    doom cu
    war2 full
    war2 cu

    #19342

    BuckoA51
    Keymaster

    Nice, I was meaning to test this more thoroughly. My TV won’t do the 70hz modes sadly (that’s to be expected).

    #19345

    James-F
    Participant

    Although, it would be ideal to have 640×400 and 720×400 70Hz (449p) modes for PC RGBHV, because 384p is somewhat dodgy and requires extensive advanced timing tweaks, I don’t think it was meant for PC input anyway.

    Marqs you there?

    EDIT:
    Proper 640×400 mode was added to firmware v0.81.

    #22588

    James-F
    Participant

    Here are my advanced timing setting for 400 mode for retro PCs with OSSC firmware v0.81.
    This will result in no overscan and will show in perfect 4:3 on a PC monitor (not TV) with HDMI input.
    Note that 400p mode is 70Hz and TV don’t like that at all, but PC monitors do.

    480p in sampler: VESA 640×480@60
    Allow upsample2x: On
    384p proc: Line2x
    480p/576p proc: Line2x
    TX mode: DVI

    640×400 (PC mode)
    —————–
    H. Samplerate : 700
    H. Synclength : 62
    H. Backporch : 54
    H. Active : 576
    V. Synclength : 2
    V. Backporch : 18
    V. Active : 432

    #22594

    bamf226
    Participant

    Do these settings change for higher resolutions (800 x 600 or 1024 x 768)?

    Can this work in 60Hz to use on an HDTV?

    #22601

    NoAffinity
    Participant

    Thank you for posting the screenshots. I see people using these old school PC’s with the OSSC, and am always interested in what is being played. Congrats, looks great!

    #22603

    James-F
    Participant

    Can this work in 60Hz to use on an HDTV?

    The OSSC does not change refresh rate, what comes in is what comes out.
    I don’t think an HDTV will take 70Hz resolutions, so it’s mainly for modern PC monitors.
    I may be wrong so give it a try.

    #22633

    root42
    Participant

    So I tried your timings, but they lead to no sync at all when in text mode. Since the DOS text mode is also 400 lines, I do not see an option to use those settings, apart from loading a preset when running a game, which I find inconvenient. I use these settings in VGA text mode (720×400@70 Hz) on my 286 PC (currently with Trident 9000, but also with ET4000):

    H. samplerate 874
    H. synclen 104
    H. backporch 51
    H. active 741
    V. synclen 2
    V. backporch 32
    V. active 405

    This is obviously the same settings that is used for 320×200 games under DOS.

    Windows runs in 640×480@60 Hz using these timings:

    H. samplerate 850
    H. synclen 59
    H. backporch 56
    H. active 720
    V. synclen 2
    V. backporch 30
    V. active 480

    This leads to a good picture, although 2 lines or so at the bottom are missing. But so far I am not bothered.

    #22634

    root42
    Participant

    Interesting enough, using Line2X makes the 480 mode worse. See the screenshots below for an example. Both screenshots are shot with reset settings in 640×480@60 Hz:

    Default settings with passthru

    Default settings with Line2x

    And with Line2x disabled, but DTVP sampler I get this (it has some noise, black and white edges are flickery), it at least shows the whole screen:

    Default settings with DTVP sampler

    #22639

    James-F
    Participant

    So I tried your timings, but they lead to no sync at all when in text mode.

    These settings work perfectly well on all my LCD PC monitors in text mode 720×400@70Hz as you can see on the first post of this thread, playing Doom (320×200) and Norton Commander (640×400).
    I do not see any artifacts nor the corners cut off (no overscan).
    Note that the resulting resolution will be 1152×864 (XGA+) with 384p Line2x which is in a VESA standard and works on all PC Monitors, but when not using Line2x the base 576×432 resolution is NOT part of the VESA standard.
    You can raise H.Samplerate if you have overscan and recenter with Backporch and/or Synclength.

    With 640×480@60Hz (320×240) modes, I see no artifacts nor overscan.
    Note that when using upsample2x you should always use Line2x for 480p modes since upsampling requires higher resolution to not look jaggy.
    Remember that using Line2x for 480p will output 960p, that PC monitors love, but TV’s hate.

    What PC monitor are you using?

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