V.backporch – Increase upper limit

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This topic contains 3 replies, has 3 voices, and was last updated by  Harrumph 3 weeks ago.

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    Going by my calculations, I’m going to need to use a H.backporch of 303-304 in order to establish if I can get Lx5 using a Saturn and outputting the OSSC to Panasonic plasma.

    Seems logical based on the various settings I’ve recorded anyway OSSC settings for Panasonic VT60

    I’d rather the sharp pixels of optim modes, but the settings indicate a pattern for generic 4:3, whereas optim has the same tweaker settings across linemulti modes so I have no idea what to mess around with.



    If you’re aiming for 1920×1080, there’s very little space for horizontal back&front porches. The default L5 mode (1536×240) has samplerate of 2046, so (2046-1536)=510 pixels is available for backporch, sync and frontporch. However, following active area adjustments are applied internally to achieve 1920×1080 format:

    1. H.synclen is reduced by 120 (150->30 in default case), effectively increasing H.frontporch to 247
    2. Required active area expansion to both sides is calculated: In default case (1920-1536)/2=192
    3. H.backporch and H.frontporch are reduced by the amount defined in (2). In default case H.backporch 234->42, H.frontporch 247->55
    4. is reduced by 24, V.backporch is increased by 12.

    Maximum valid H.backporch parameter (with default H.samplerate & H.synclen) would thus be 42+55+192=289, otherwise H.frontporch would get negative.

    If you use 1600×1200 format and 320×240 mode, then all H.values are internally multiplied by 5 (so you can get effective H.backporch of 305) and only (1) of the steps above is applied. You can then manually do and V.backporch+=12 if you want 1600×1080 output instead.



    EDIT: nevermind. Just figured it out 🙂

    • This reply was modified 3 weeks ago by  BonzoBits.


    Interesting. Perhaps the same approach of active area adjustment can increase compatibility of Lx3 mode also?

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