[mythtv-users] DirectFB output and fb modelines

papenfuss at juneau.me.vt.edu papenfuss at juneau.me.vt.edu
Wed Feb 18 07:49:50 EST 2004

	I'm not sure that I can help much, but I can fill in a couple of gaps.  
I've got a slightly similar situation, but for a different reason.  I was 
trying to get the console framebuffer (with an aty128fb on an ATI card) to work 
at a custom resolution.  I need a custom resolution because I'm driving the 
NTSC TV directly with the VGA port (through a modulator, not a scan converter).  
Bottom line is I need *exact* VGA timings for NTSC compatibility, *AND* 
interlaced support.  What I found was a mess of framebuffer timings and 
modelines scattered throughout /etc/fb.modes (for fbset userspace programs), 
and within <kernel-src>/drivers/video/aty128fb.c and modedb.c.  I hacked the 
aty128fb source to allow interlaced modeline (I think, anyway), but I couldn't 
set it to be at any resolution I wanted.  Although I brewed up a specific 
15.7kHz/30Hz/Interlaced modeline in /etc/fb.modes, changing to it didn't take.  
It found something "close" and used that.  I suspect it's the kernel 
framebuffer driver trying to protect you from yourself and picking a "real" 

	You can probably look through the <kernel-src>/drivers/video/matrox/* 
files and make something out of it.  It went beyond my threshold of care this 
past weekend so I haven't looked any further into it.


On Wed, 18 Feb 2004, Juha Pahkala wrote:

> Hello,
> I've finally recently started to setup a MythTV box and already now
> wondering why it took me so long to start :) MythTV absolutely rocks!! So
> thanks to all of you guys who made this happened.
> Anyway, let's get to the point. I've set up myth box without xfree, ie.
> using QT/Embedded and DirectFB. I've now got it running but I'm having a
> problem with DFB and framebuffer modelines. This is the case: I've got a
> Matrox G400, which is quite picky with the timings of the tv-out, but I've
> got a modeline in /etc/fb.modes that works reasonably well. And this is
> the modeline that mythfrontend runs on, since the qt/e part uses directly
> the framebuffer. But, when I try to watch tv (using a DVB-C card),
> directfb switches the resolution to '704x576' for some reason, and all I
> can see on the tv is green bars.
> I've tried to look through the menus and mailinglists, but haven't found
> an answer to this question: Where does directfb fetch the modeline from?
> How can I control that? I know it doesn't use /etc/directfbrc, since I've
> got the proper '720x576' mode set up there. And I don't have an entry
> matching the '704x576' that dfb chooses in my /etc/fb.modes. So I'm pretty
> clueless here.
> Could somebody explain this to me?
> TIA, juhis
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