can't set 60hz v refresh rate

Tue Oct 18 22:11:56 UTC 2005

Stuart Sears wrote:
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> sean enlightened us with the following gems on 15/10/05 18:34:
> 
>>David Becker wrote:
>>
>>
>>>sean wrote:
>>>
>>>
>>>>On fc4, updated, I have a dell flat screen with a intel i915g chips -
>>>>using xoreg i820 - that I want to run at 1280x1024x60.
>>>>
>>>>Desktop-> Preferences -> Screen Resoltuion does not let me change the
>>>>refresh rate. It stays at 75hz.
>>>>
>>>>I hand edited xorg.conf so that the monitor section has
>>>>
>>>>VertRefresh   60
>>>
>>>
>>>
>>>It's best to leave these values at whatever your monitor specifies.
>>>
>>>If X doesn't automatically choose a suitable modeline for your monitor
>>>(I assume you have some kind of TFT that doesn't work above 60 hz), then
>>>you can calculate these values yourself;
>>>
>>>Find a modeline calculator on the net. Given your monitor's
>>>characteristics, they allow you to fix one or more parameters (such as
>>>Vertical refresh rate and resolution) while finding the modeline values
>>>to accommodate.
>>>
>>>Copy the result of the modeline calculator to the 'Monitor' section of
>>>xorg.conf.
>>>
>>>I for instance used this to calculate a suitable interlaced
>>>(exaggerated) 200Hz frequency for PAL television viewing as in:
>>>
>>>Section "Monitor"
>>>        Identifier   "LG915FTPlus"
>>>        VendorName   "LG"
>>>        ModelName    "915FTPlus"
>>>        HorizSync    30.0 - 107.0
>>>        VertRefresh  50.0 - 200.0
>>>        Option      "dpms"
>>># TV (PAL) Viewing
>>># Measured xawtv dimensions at 760x573
>>># 200hz
>>>        Modeline "760x573 at 200i" 64.46 760 792 1032 1064 573 582 593 603
>>>interlace
>>>EndSection
>>>
>>>Then insert or append the modeline identifier ("760x573 at 200i") to the
>>>list of Modes in the 'Screen' section of xorg.conf.
>>>
>>>Regards,
>>>
>>>    David
>>>
>>>
>>
>>
>>Great idea. I'll try it.
>>
>>sean
>>
> 
> there is a built-in Modeline calculator on your system, called gtf
> syntax (for 1024x768@ 60Hz):
> gtf 1024 768 60
> should generate output a bit like
> # 1024x768 @ 60.00 Hz (GTF) hsync: 47.70 kHz; pclk: 64.11 MHz
>   Modeline "1024x768_60.00"  64.11  1024 1080 1184 1344  768 769 772 795
>  -HSync +Vsync
> you can drop the -HSync +Vsync bit, and this would give you a modeline
> (in your Monitor section of xorg.conf)...
> Modeline "1024x768" 64.11  1024 1080 1184 1344  768 769 772 795
> 
> I used to have to do this for my Dell widescreen laptop.
> 
> Regards
> 
> Stuart

This seemed like a much better idea before I started poking 
arooung. I used gtf and four web based modeline calculators.

They each gave a different result!!
Is this engineering or mysticism?

  gtf 1280 1024 60

   # 1280x1024 @ 60.00 Hz (GTF) hsync: 63.60 kHz; pclk: 
108.88 MHz
   Modeline "1280x1024_60.00"  108.88  1280 1360 1496 1712 
1024 1025 1028 1060 -HSync +Vsync

http://www.dkfz-heidelberg.de/spec/linux/modeline/

Horizontal Resolution: 	 1280
Vertical Resolution: 	1024

Vertical Refresh Rate: 	60.00 Hz
Horizontal Refresh Rate: 	63.73 KHz
Dot Clock Frequence: 	109.62 MHz

# V-freq: 60.00 Hz  // h-freq: 63.73 KHz
Modeline "1280x1024" 109.62  1280 1336 1472 1720  1024 1024 
1026 1062

http://xtiming.sourceforge.net/cgi-bin/xtiming.pl

XFree86 Modeline
Put the following modeline in your XF86Config in the 
Monitors section, and add it to your active modes in the 
Screen section. Use this modeline at your own risk.
Modeline "1280x1024 at 60" 114.98 1280 1312 1744 1776 1024 1045 
1055 1076
Horizontal sync frequency: 64.73 kHz

http://koala.ilog.fr/cgi-bin/nph-colas-modelines

Colas XFree Modeline Generator results
Computed by http://koala.ilog.fr/cgi-bin/nph-colas-modelines
Max Bandwidth: 200 Mhz
Max Vertical Frequency: 60 Hz
Max Horizontal Frequency: 100 Khz
Minimun Refresh Rate: 60 Hz Min Bandwidth: 20 Mhz
Min Horizontal Frequency: 30 Khz

ModeLine "name" dotclock width x x x heigth y y y #RefreshRate

   ModeLine "1280x1024" 110.31 1280 1336 1616 1728 1024 1026 
1038 1064 #60Hz

http://zaph.com/Modeline/

# 1280x1024 @ 60Hz,  63.42 kHz hsync
     Mode "1280x1024"
     DotClock    100.96
     HTimings  1280 1312 1416 1592
     VTimings  1024 1027 1030 1057
EndMode

sean