[Openchrome-users] SP13000 + fuzzy vga output at high resolutions

[Xavier Bachelot]

Luc Verhaegen wrote:
> On Thu, Jan 18, 2007 at 10:02:14AM +0100, Xavier Bachelot wrote:
> 
>>Luc Verhaegen wrote:
>>
>>>On Wed, Jan 17, 2007 at 03:13:38PM +0100, Xavier Bachelot wrote:
>>>
>>>
>>>>brightman wrote:
>>>>
>>>>
>>>>>SP13000 + fuzzy vga output at high resolutions
>>>>>I was thinking about buying an SP13000 board and driving the VGA output 
>>>>>at the same resolution as my LCD which would mean a resolution of 1680 x 
>>>>>1050. 
>>>>>Firstly is this reasonably straighforward using the openchrome drivers 
>>>>>(is there an easy way to fathom out a suitable modeline, I've used 
>>>>>powerstrip in the past?)
>>>>>
>>>>
>>>>The modeline won't be hard to get. Just run 'gtf 1680 1050 60 -x' and 
>>>>stick the output into your xorg conf.
>>>>
>>>>
>>>>
>>>>>Secondly I've been reading on a couple of VIA related forums about 
>>>>>problems with the VGA output on SP13000 boards at resolutions of 1280 x 
>>>>>1024 (and higher). 
>>>>
>>>>However, and I don't know if it's related to the above mentioned 
>>>>fuzziness pb, high resolutions will require a lot of bandwidth, so the 
>>>>ram type you are using might come into the game.
>>>>
>>>>Regards,
>>>>Xavier
>>>>
>>>
>>>In this case, using cvt -r might relieve the problem. 1680x1050 is a 
>>>resolution for a TFT based monitor, so reduced blanking should be 
>>>preferred if you're providing modelines anyway.
>>>
>>>Luc Verhaegen.
>>>http://unichrome.sf.net/
>>
>>Thx for the info, Luc. What are the differences between gtf and cvt 
>>apart from the reduced blanking switch ?
>>
>>Is there a good explanation of reduced blanking somewhere ? I think I 
>>got it mostly, but would be unable to properly explain it to someone 
>>else. And just to be sure, can reduced blanking be used on any TFT w/o 
>>pb ? Using reduced blanking on a CRT simply won't work or will it also 
>>damage the screen ?
>>
>>Regards,
>>Xavier
>>
> 
> Normal timing is just a simplified calculation.
> 
> I'm not sure, it's pretty straightforward. No need to shift an electron 
> beam, no need to spend as much time on sync, and, you also don't have 
> big edges hidden behind the monitors frame.
> 
> You can try reduced blanking on a CRT reasonably safely. You just have 
> the edges wrapped a bit. Nasty, but not that unsafe. You just don't want 
> to use it all the time, which is logical for a sane person, as it really 
> is a buggered mode. I think that fear of monitor damage is quite 
> overrated. And i _have_ killed at least one CRT by testing; it's about 
> extensive repitition, not about accidentally doing the wrong thing a few 
> times.
> 
> It should work quite happily on a definitive number of TFT based 
> screens (there's no 100% certainty of course), whether they use a 
> digital link or not. The big problem is that VESA EDID does tell you 
> that you have an analog or digital link, but it doesn't bother with 
> telling you whether it allows reduced blanking or not.
> 
> Most people treat the digital bit as definitive, but it isn't. CRTs do 
> exist with DVI-D.
> 
> Luc Verhaegen.

Thx for the explanations.

Regards,
Xavier