[mythtv-users] Minor Screen Refresh Visible

Petteri Matilainen pmatil at gmail.com
Wed Jul 30 17:01:44 UTC 2008

Dan Ritter wrote:
> On Wed, Jul 30, 2008 at 09:28:44AM -0400, C.T. Paterson wrote:
>> 2008/7/30 Dan Ritter <dsr-myth at tao.merseine.nu>:
>>> On Wed, Jul 30, 2008 at 08:39:54AM -0400, C.T. Paterson wrote:
>>>> 2008/7/30 Petteri Matilainen <pmatil at gmail.com>:
>>>>> VGA->SCART adapter cable. Do I need to modify the xorg.conf modeline?
>>>>> Any help is greatly appreciated.
>>>> My experience does not suggest I had a modeline problem - but it's
>>>> possible.  Where did you get yours from?  I've got an LCD HDTV, and
>>>> some of them are known to supply incorrect modelines to Xorg (google
>>>> for a "UseEDID" xorg option).  Mine appeared to be one of them, so I
>>>> obtained mine by running "gtf" on the command line, and used the
>>>> generated modeline in my xorg.conf.
>>> You could certainly be running with a modeline that your LCD
>>> does not quite like. I just acquired an LCD, and discovered that
>>> the NVidia built-in 1920x1080_60 mode was horrendously
>>> overscanning horizontally. The manual contained all the required
>>> timings, though, and I built a perfect modeline out of that.
>> If you're inclined, Dan, I'd be interested to know how.  My knowledge
>> of modelines is pretty slim - and while my manual has a bunch of
>> information in it - I wouldn't know how to construct a modeline out of
>> it (although gtf seems to have served me well).  I'm merely curious.
> What LCD do you have? Is the manual online? I'd be happy to
> help.
> An X modeline is not black magic; it's a list of timings, mostly
> in terms of pixels:
> Rate HDisplay HSyncStart HSyncEnd HTotal VDisplay VSyncStart VSyncEnd VTotal
> You know the HDisplay and VDisplay fields immediately: those are
> the visible pixels. The Rate is the pixel clock, in millions per
> second. That should be in the manual.
> Manuals like to specify FrontPorch, BackPorch and Sync;
> considers there to be offsets to add to the previous entry, so
> we get:
> HDisplay
> HSyncStart = HDisplay + FrontPorch
> HSyncEnd = HSyncStart + BackPorch
> HTotal = HSyncEnd + Sync
> Then, for vertical timing, it works out the same way.
> Adding +/- HSync and +/- Vsync flags indicates the polarity of
> the signals; again, that should be in the manual.
> -dsr-
Sorry to jump in, but I have a 16:9 CRT TV, for which I don't know the 
correct timings. "Standard PAL" from mythwiki is not it, because there's 
too much overscan IMO and the picture is not centered (seen when in 4:3 
mode). I'll have to play with modeline when I have the time. Don't know 
how modeline affects the vertical "artifacts".


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