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-   -   Which pixel clock rates are available ? (http://www.nvnews.net/vbulletin/showthread.php?t=34103)

jsmerritt 08-06-04 09:05 AM

Which pixel clock rates are available ?
Does the NVidia driver (e.g. 6106) allow you to set the pixel rate clock to any reasonable value, or are you limited to a smaller set of fixed clock rates ???

As described in: <http://www.nvnews.net/vbulletin/showthread.php?t=34040>
the X-Server appears to be accepting my mode lines, but the pixel clock rate does not change on the info screen pop-up facility on the display monitor. (1600x1200 DVI GeForce FX5200)

I am trying to determine if my mode lines are being ignored or if the info screen on my display is incorrectly reporting the pixel clock rate. Suggestions appreciated.
Thanks, Scott.

Thunderbird 08-06-04 09:27 AM

Re: Which pixel clock rates are available ?
In the nvidia driver readme you can find in appendix L lots of info about programmind modelines including the capabilities of your card. On current cards the frequency of the ramdac is lets say 350MHz or perhaps even more now, so this is the max pixelclock. Note that your monitor ofcourse needs to like that pixelclock too. These days most vendors don't tell what the max bandwith (== max alowed pixelclock) of their monitor is :(

jsmerritt 08-06-04 10:15 AM

Re: Which pixel clock rates are available ?
Yes, have looked through Appendix L. I believe my mode lines are OK since they were generated by "videogen" and pass it's NVidia check - and also the X-Server seems to accept them. Unfortunately, the DVI cable rate (<= 162 MHZ) is much more limiting than either the DAC limited rate on the video card or the max bandwidth limit on the monitor.

So from your response, it sounds like a SHOULD be able to "demand" a pixel clock rate of 156.92 rather than 162 MHz from my video card. I'm assuming that my monitor IS correctly reporting the pixel clock that it is seeing - because it does see/report a different pixel rate when the video card is displaying the boot console through the video BIOS (also at 1600x1200). Short of finding a high bandwidth oscilliscope, I don't know how else to confirm the true pixel clock rate.

Unless someone else is aware of another limit on the available DVI pixel clock rates, sounds like I might need to file a bug report ...

Thanks for the reply - Scott.

Thunderbird 08-06-04 10:20 AM

Re: Which pixel clock rates are available ?
I wonder if changing the pixelclock is usefull when using a lcd screen as there's no real refresh rate. The bottleneck are the crystals themselves.

jsmerritt 08-06-04 10:54 AM

Re: Which pixel clock rates are available ?
1 Attachment(s)
Yes, refresh speed is not as much of an issue with digital flat panel displays - accept as a "means" to have changes more quickly reflected on the display (e.g. in a gaming environment).

But, cable limitations are a problem. Custom mode lines, with reduced blanking intervals *are* used by some flat panel users. This is required, for example, if one attempts to drive one of the 1920x1200 flat panel displays using a single link DVI connection. The blanking interval must be reduced in order to lower the pixel clock into the range supported by the DVI standard (TMDS) and their driver chips.

My XFree86 log (attached) includes a section that starts with "Supported additional video mode". My guess is that this mode is somehow overriding my custom mode line ... :( But I am stumped as how to proceed further ...

Thanks, Scott.

Thunderbird 08-06-04 11:38 AM

Re: Which pixel clock rates are available ?
Actually the logfile is quite clear:
(WW) (1600x1200,Monitor0) mode clock 175.5MHz exceeds DDC maximum 170MHz
(WW) (1600x1200,Monitor0) mode clock 189MHz exceeds DDC maximum 170MHz

So basicly your modeline is not correct according the nvidia driver also note that the driver complained about bad vsync ranges for both screens:(II) NVIDIA(0): Processing requested modes for display device DFP-0:
(II) NVIDIA(0): "1600x1200_DVI"
(WW) NVIDIA(0): The user specified VertRefresh "30.000-85.000" has been
(WW) NVIDIA(0): adjusted to "50.000-85.000" (the intersection with
(WW) NVIDIA(0): EDID-specified VertRefresh "50.000-85.000"
(II) NVIDIA(0): Monitor0: Using hsync range of 30.00-92.00 kHz
(II) NVIDIA(0): Monitor0: Using vrefresh range of 50.00-85.00 Hz

jsmerritt 08-06-04 12:52 PM

Re: Which pixel clock rates are available ?
1 Attachment(s)
Thunderbird, Thanks again for hanging with me on this one.

I've attached my XF86Config file (which I probably should have done earlier -sorry). It is my understanding that all of those modes that are considered (and rejected) are XF86 *default* modes. I've tried to eliminate them (by commenting the "modes" line in the monitor section), but they are still there.

Please correct me if I misunderstand, but I believe that my custom mode line which is labelled "1600x1200_DVI" is the one that is finally accepted and installed by X server. Also note that this line has the pixel clock rate reduced to 156.92.

Thanks again, Scott.

PS - Yes, I've been meaning to fix that errant refresh limit.

Thunderbird 08-06-04 01:23 PM

Re: Which pixel clock rates are available ?
I'm not sure how the nvidia drivers come to that 175MHz (perhaps because of the corrected vrefresh range). What happens when using this modeline:
ModeLine "1600x1200_60" 161.0 1600 1704 1880 2160 1200 1201 1204 1242 -hsync +vsync

jsmerritt 08-06-04 01:43 PM

Re: Which pixel clock rates are available ?
2 Attachment(s)
XServer (appears to) accept your mode line. Screen display looks fine.
However, on-screen pop-up window still shows Clock = 162.00 MHz, HF=75.18 KHz, VF=60.0 Hz :( Also, I fixed errant refresh range - no apparent effect .... Config and Log file attached.

Thanks, Scott.

Thunderbird 08-06-04 03:34 PM

Re: Which pixel clock rates are available ?
What do you want to do then?

jsmerritt 08-06-04 04:15 PM

Re: Which pixel clock rates are available ?
>> What do you want to do then?

I'm not sure I understand your question. Does it seem to you that the X-Server is "ignoring" the custom mode line (since the pixel clock indicated by the monitor is still 162) ? If so, should I file a bug report, or is there something else to try ?

Thunderbird 08-06-04 04:20 PM

Re: Which pixel clock rates are available ?
Oops, the last question I thought it was working fine (didn't look at the files), that's why I asked the question. Don't know why it doesn't work now. You could add the option to ignore the bandwith (DisableBandwithTest or something like that) and then check what the monitor shows.

Else I don't know.

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