[Novalug] xorg.conf -- gtf command and mode lines

Nino Pereira pereira@speakeasy.net
Sat Oct 17 13:25:10 EDT 2009


Thank you for all the discussion.

I substituted the suggested changes on one of my computers
(the one with the Matrox chip, confirmed by 'lspci'). It worked.

I had to buy a video card for one of the computers to use the LCD screens.
So, I got a Radeon HD3450. This one was recognized by Ubuntu, and the
screen worked well. On another one there's a nVidia NV11. This one works too.

It's nice to learn all these things, but I sometimes wish it wasn't necessary.

Nino


Bryan J. Smith wrote:
> I think his Matrox G550 has a clock limited to 157MHz.  Not sure, haven't
> had a Matrox since the G400/450 series.
> 
> Until my suggestions are attempted, I'm not going to respond further.  I can
> only open the door to suggestions, I can't make people walk through them.
> 
> In a nutshell, giving less information to X is best, not more.  Let the card and
> monitor use DDC to talk, and then try without DDC, etc...  Modelines are rarely
> needed these days, as X already knows (and will use) the VESA standards.
> 
> 
> 
> 
> ----- Original Message ----
> From: Jon LaBadie <novalugml@jgcomp.com>
> To: NOVALUG <novalug@calypso2.tux.org>
> Sent: Fri, October 16, 2009 7:33:34 PM
> Subject: Re: [Novalug] xorg.conf -- gtf command and mode lines
> 
> On Fri, Oct 16, 2009 at 08:59:32AM -0400, Nino Pereira wrote:
>> On defining scan frequencies:
>>
> 
> Nino mentioned he used a program, "gtf" in /usr/bin to generate
> his X timings.  Although he did not use them, gtf can also
> create a mode line appropriate for the resolution.  For example:
> 
> $ gtf 1920 1200 60 -x 
> 
>   # 1920x1200 @ 60.00 Hz (GTF) hsync: 74.52 kHz; pclk: 193.16 MHz
>     Modeline "1920x1200_60.00"  193.16  1920 2048 2256 2592  \
>                                         1200 1201 1204 1242  \
>                     -HSync +Vsync
> 
> I thought I knew a tiny bit about X mode lines, having figured
> one out from a manufacturer's spec's a long time ago.  If I
> recall correctly, the 4 numbers "1920 2048 2256 2592" define
> a horizontal sweep timing as totalling 2592 pixels, 1920 of
> which are in the viewable area, ending at 2048 pixels, and
> horizontal sync can start at 2256 pixels.
> 
> The thing I don't get is how can gtf know that mode line will
> be suitable for any specific monitor.  I.e. that it will run
> at a 193.16MHz pixel clock rate, that the leading overscan
> will be 128 pixels before the viewable area, that each screen
> update will be 1242 scan lines, etc.?  Seems to me that it is
> just one of many possible mode lines depending on the properties
> of the monitor electronics.  Or am I just too old ;)
> 
> Jon



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