[mythtv-users] Re: problem getting interlaced output

[Cory Papenfuss]

> Cory, thanks for the info. I had been using a something like:
>
> Horizsync 10-90
> VertRefresh 10-120
>
> I had thought that these numbers only served as upper and lower limits and 
> that the actual frequencies were somehow derived from the modelines. I tried 
> the mode lines that I had tried before with the specific frequencies that you 
> suggested but the main difference was that no modes validated so I couldn't 
> even start X. I guess that's because I am now limiting the frequency ranges 
> to a single pair of values. On one attempt, the error was "hsync out of 
> range" instead of "vsync out of range" Does that mean I'm getting closer?
>
 	You were right... those two lines are there to protect you from 
yourself.  If you set those to values that your monitor can do, then when 
X fires up it will invalidate any mode that produces frequencies outside 
the range that was specified for a monitor.  If you open it wide open like 
you did (10-90H, 10-120V), you can code up whatever you want and unless 
the card balks at the programming due to other reasons, it'll spit out 
whatever you ask for.

> What is the relationship between the dotclock value in the modeline and the H 
> and V frequency values?
>
 	Take a look at what was added to the wiki from a post of mine:
http://www.mythtv.info/moin.cgi/ModeLinesHowTo_2fDoItByHand

 	Basically, remembering that the 1st number is *10^6,
Hfreq = 1st number/5th modeline number
Vfreq = 1st number/(5th number * 9th number)

> Is it correct that for interlaced TV, the 29.97 number is frames/sec and the 
> 59.94 number is fields/sec? Which of these two numbers goes on the 
> VertRefresh line?
>
 	The actual speed of the vertical oscillator.... in other words, 
60.

> Here is the relevant section of my xorg.config file. Should this have worked?
 	Probably not.

> 	HorizSync    15.734
 	Probably make it 15.5-16

> 	#VertRefresh  29.97
> 	VertRefresh  59.94
 	Again, make it a range around the right freq

> 	#ModeLine "ATSC-480-60i" 11.97 640 664 736 760 480 484 492 525 
> Interlace
> 	#Modeline "640x480i" 14.16 640 712 776 904 480 532 537 625 interlace 
> -hsync -vsync
> 	#Modeline "coryntsci" 14.3 720 760 824 912 480 484 492 525 interlace 
> -hsync -vsync
> 	Modeline "coryntscpi" 28.6 720 760 824 912 480 484 492 525 interlace 
> -hsync -vsync

 	Did you only *want* the progressive scan mode?  That one is 2x the 
Hfreq... basically standard VGA at 60Hz, just 720x480.  In that case, you'll 
need 31kHz as a valid Hfreq.  Also, since you specified it as interlaced, 
you'll get 120Hz vertical output.

> (II) NVIDIA(0): Clock range:  12.00 to 300.00 MHz       <----------- Does 
> this mean that the modeline with the 11.97 dotclock will never work?
 	Yes... but it's probably "close enough" that you could use it.  If 
in doubt, change the 5th number by the ratio of 12.00/11.97

> (II) NVIDIA(0): Not using mode "coryntscpi" (hsync out of range)


 	Just as a note to the wiki page.  The honest-to-goodness NTSC mode 
I found:
Modeline coryntsci 14.318 720 760 824 910 480 484 492 525 interlace

is not liked by the nvidia driver since 910 is not divisible by 8.  That 
can be fixed with a slight adjustment:

Modeline coryntsci 14.350 720 760 824 912 480 484 492 525 interlace

 	Do the math... it still works out to the right frequencies.

-Cory
*************************************************************************
* Cory Papenfuss                                                        *
* Electrical Engineering candidate Ph.D. graduate student               *
* Virginia Polytechnic Institute and State University                   *
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