Widescreen Passthrough modes

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  • #22629

    I want to use my OSSC with an Acorn RISC PC which can output a variety of resolutions including various 50Hz 625 line TV modes so that I can line double those modes and pass through higher resolution modes.
    This works and I can switch between TV modes such as 640×256 and higher resolution VGA modes like 1280×1024 or 1600×1200 and the picture quality is excellent but I’m using a widescreen monitor so I want to use the RISCOS desktop in a widescreen mode.
    As far as I can tell, OSSC only supports 1920×1080 @ 60Hz and the RISC PC can’t generate that resolution as it’s just a little beyond it’s video memory bandwidth but it can generate 50Hz HD modes.

    At the moment I’m using a 16:10 monitor so the best resolution I could use is 1680×1050 @60Hz but I may switch to a 16:9 monitor in future which would use 1920x1080p50.

    The OSSC doesn’t seem to work with standard 50Hz HD modes (1920x1080p50, 1920x1080i50 and 1280x720p50) as the video is displayed squashed up to the left with a large black border on the right and the advanced timing adjustments don’t seem to be able to fix this.
    (I think thats due to standard 50Hz HD modes using the same pixel clock as 60Hz modes and then using a very large front porch to make up the time difference)

    Would it be possible to add support for 50Hz HD modes and additional widescreen modes like 1680×1050 @60Hz in passthrough mode or maybe some way for user defined addition of such resolutions?

    I’ve compiled a list of modelines with standard VESA timings for all widescreen modes excluding 60Hz HD modes which are already supported:

    16:10 modes:
    1280×800@60Hz Modeline “1280×800” 83.5 1280 1352 1480 1680 800 803 809 831 -hsync +vsync
    1440×900@60Hz ModeLine “1440×900” 106.5 1440 1520 1672 1904 900 903 909 934 -Hsync +Vsync
    1680×1050@60Hz Modeline “1680×1050” 146.25 1680 1784 1960 2240 1050 1053 1059 1089 -hsync +vsync
    1920×1200@60Hz Modeline “1920×1200” 154.00 1920 1968 2000 2080 1200 1203 1209 1235 +HSync -Vsync

    16:9 modes:
    1360×768@60Hz Modeline “1360×768” 85.500 1360 1424 1536 1792 768 771 777 795 +hsync +vsync
    1600×900@60Hz Modeline “1600×900” 108.00 1600 1624 1704 1800 900 901 904 1000 +hsync +vsync

    50hz HD modes:
    1280x720p50 ModeLine “1280×720” 74.25 1280 1720 1760 1980 720 725 730 750 +HSync +VSync
    1920x1080i50 ModeLine “1920×1080” 74.25 1920 2448 2492 2640 1080 1084 1094 1124 +HSync +VSync Interlace
    1920x1080p50 ModeLine “1920×1080” 148.50 1920 2448 2492 2640 1080 1084 1089 1125 +HSync +VSync


    Are you sure you’ve tried adjusting adv. timings for correct mode? At least 720@50Hz you should be able to tune perfectly by tweaking the parameters. For 50Hz HD modes in general, the detection system has to upgraded since currently is selects the presets solely based on total line count.


    I haven’t tried 720p50 as the RiscPC can generate 720p60 but it’s too low a resolution for a practical solution and the wrong aspect ratio for me at the moment anyway as I’m currently using a 16:10 monitor.
    If I select 1080p50, it’s correctly recognised as 1125p @ 50hz by the OSSC LCD display but the advanced timing adjustments max out without being able to set them correctly although changing them does make a visible difference so I am adjusting the correct mode.
    e.g. the H samplerate defaults to 2200 which is correct for 1080p60 but it should be 2640 for 1080p50 due to the large front porch and the adjustment maxes out at 2300.

    So I guess I’m looking for an increase of the range of adjustment of the H samplerate so that the 1080 50hz modes can be brought into alignment (or as you mention a code change to auto switch 50/60) and the addition of the rest of the above VESA timings (or at least 1680×1050 if there are memory space issues) to the timing table which appears to be in video_modes.h


    H samplerate maximum is bumped to 2800 in upcoming v0.82 firmware.


    Thanks for the update.

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