Am i correct (CVT is broken!)

fennectech · 2014-10-31 19:37:49

well over the past few days ive been spending alot of time getting a new display to operate under linux. the problem with it is this display REQUIRES 1366x768 ive seen other DFPs that have the same requirement or even a more exotic resolutions and the CVT utility is unable to calculate resolution for 1366x768 and rounded to 1368x768 and it didnt work with the panel so my solution was to explore the web and i found this website with tons of modelines so after 2.5 hours of trial and error i found a modeline that actually worked for this DFP and it was a 1366x768 resolution anyways this raises question to me about the CVT utility and if it can create resolutions such as this and it cannot it appears that it only generates resolutions that are multiples of eight therefor there are many resolutions that cannot be generated with it so im posing the point that the utility may need modification or rewriting not saying im right but just posing an theory and idea i have.

fennectech · 2014-10-31 19:42:26

and anyways i did figure out how to get it to work and the lc320EM uses these modelines "1920x1080" 148.5 1920 2008 2052 2200 1080 1084 1089 1125 +hsync +vsync and "1366x768" 85.50 1366 1424 1536 1786 768 771 777 795 +HSync +VSync

Lone_Wolf · 2014-11-01 14:35:07

CVT is intended to generate modelines for CRT devices, and i don't think i've ever seen a 1368x768 CRT .

All DFPs (= digital flat panel ) are supposed to send an EDID that has all necessary modeline information.

Why did you want to calculate your own ?

fennectech · 2014-11-01 15:11:25

my DFP did noy send any modeline information and thus i could not use the resolution and i know it would do the same on other linux based systems therefore i needed to find modelines online for it because there is one DFP that doesnt properly send EDID information there will be others and some users arent exactly good at troubbleshooting so the CVT utility may need a rewrite
the DFP shows up as unknown to all linux based operating systems i have so the highest resolution was 1024x768

Last edited by fennectech (2014-11-01 15:13:42)

Gusar · 2014-11-01 15:36:08

Lone_Wolf wrote:

CVT is intended to generate modelines for CRT devices

Nope, you're thinking of GTF (general timing formula). CVT (coordinated video timing) is meant for both CRT and DFP displays. However, it's still about analog signals (VGA), not digital ones (DVI). You're right that the correct modeline should come from the display's EDID. By the way, CRTs have an EDID too

@fenntech: Specifying your own modelines shouldn't be necessary, so the solution to your problem isn't hunting down random modelines, it's figuring out why the EDID isn't being read by the system. It is possible that your display doesn't have a valid EDID, but that's rare. Usually the problem is a flaky VGA cable or the nvidia proprietary driver being weird, but you haven't provided any info about your setup so it's impossible to tell where the issue is. The X log contains clues whether the EDID was read correctly.

BTW, sometimes the GPU or the display can only handle VGA resolutions that are multiples of 8, that's why CVT rounds to that. For example, our TV at home can do 1366x768 over digital connections, but 1360x768 over VGA. In contrast, an Asus display I have only has VGA input, but it can handle 1366x768 through it.

fennectech · 2014-11-01 16:01:56

WELL i took the nvidia card out so im using the built in intel card the cable im using is older but it worked fine under windows and windows was able to detect the display

Arch Linux

#1 2014-10-31 19:37:49

Am i correct (CVT is broken!)

#2 2014-10-31 19:42:26

Re: Am i correct (CVT is broken!)

#3 2014-11-01 14:35:07

Re: Am i correct (CVT is broken!)

#4 2014-11-01 15:11:25

Re: Am i correct (CVT is broken!)

#5 2014-11-01 15:36:08

Re: Am i correct (CVT is broken!)

#6 2014-11-01 16:01:56

Re: Am i correct (CVT is broken!)

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