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Old 07-17-2004, 05:04 PM   #1
0perat0r
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refresh rate


Linux has detected my monitor refresh rate (hpmx75) according to the ranges listed in the monitor's documentation. However, is there a way to set the refresh with more precision? Perhaps I am misunderstanding, but it is now "set" to a horizontal/verical range rather than to precise numbers for each. (i.e.: 30-70khz and 50-120hz).

Thanks
 
Old 07-17-2004, 05:26 PM   #2
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Run xdpyinfo and find that it does actually
run on a given (constant) frequency :)

Or use xvidtune to fix it down to your
hearts content.


Cheers,
Tink
 
Old 07-18-2004, 01:34 AM   #3
0perat0r
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Hello:

Thanks for your help with those commmands, but after over an hour of research, I'm still at a loss about how to interpret the informaion presented. When I do xdpyinfo, it gives me a lot of information, some of which I recognize, such as "supported pixel formats" and the following:

default screen number: 0
number of screens: 1

screen #0:
dimensions: 1024x768 pixels (321x241 millimeters)
resolution: 81x81 dots per inch
depths (7): 24, 1, 4, 8, 15, 16, 32

What follows are some hex values and other jargon which does not seem to be relative to refresh rate. When I do xvidtune, it pops open two windows, one of which is a warning (and disclaimer) not to fool around with these settings unless you understnad what you are doing (I do not yet), and the other is the current config info, as follows:

HDisplay: 1024
VDisplay: 768

HSyncStart: 1072
HSyncEnd: 1168
HTotal: 1376

VSyncStart: 769
VSyncEnd: 772
VTotal: 808

horizontal sync: 68.68 kHz
vertical sync: 85.00 Hz

pixel clock: 94.50

I am unsure how to calculate the refresh rate from all of this, or even how to begin adjusting it within this interface. I found a decent site (http://en.tldp.org/HOWTO/XFree86-Vid...WTO/index.html) that almost gives me an answer, but not quite. It presents a formula for calculating refresh rate:

RR = DCF / (HFL * VFL) or,
Refresh Rate = Dot Clock [or pixel clock?] / (Horizonal Sync Frequency * Vertical Sync Frequency)

I plugged in my own numbers, obtained from running xvidtune, therefore:

RR [refresh rate] = 94.50 / (1376 * 808) = 61.77566138

Does this appear accurate? Am I using the correct numbers in this formula? I feel like the answer is very close. Any help is appreciated.

Thanks!
 
Old 07-18-2004, 01:52 AM   #4
0perat0r
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correction:

I thoguht I actually should have tried these numbers in that formula, which are my horizontal and vertical syncs:

RR = DCF / (HFL * VFL)
Refresh Rate = Dot Clock [or pixel clock?] / (Horizonal Sync Frequency * Vertical Sync Frequency)

RR = 94.50 / ( 85 * 68.68 ) = 0.016189824 [???]

my original answer shoud have been:

RR = 94.50 / (1376 * 808) = 94.50 / 1111808 = 8.49967e-05 [???]

my math was wrong the first time. Now, all of this makes even less sense

There has to be a more straightforward way of getting the refresh rate value.

help please and thank you
 
Old 07-18-2004, 04:28 AM   #5
0perat0r
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OK, I figured out that this formula does work for checking what refresh rate your hardware is set to. My math was incorrect before, so here is the complete procedure:

opened up xvidtune and got the following vital numbers for the equation:

HTotal (or HFL): 1376
VTotal (or VFL): 808

Pixel Clock (or DCF): 94.5

The formula works if you remember that the refresh rate is in Hz:
RR = DCF (MHz) / (HFL * VFL)

RR (Hz) = 94500000 / (1376 * 808)
RR (Hz) = 94500000 / 1111808
RR = 84.99669008 Hz

I validated this bytrying it with a 75Hz refresh rate scenario:

HTotal: 1312
VTotal: 800

PixelClock: 78.75

RR = 78750000 / (1312 * 800)
RR = 78750000 / 1049600
RR = 75.02858232 Hz

Then again for a refresh of 70 Hz, for good measure:

HTotal: 1328
VTotal: 806

PixelClock: 75

RR = 75000000 / (1328 * 806)

RR = 75000000 / 1070368 = 70.06935932 Hz

Here's a good site I found that it helped me out a lot:
http://www.hut.fi/Misc/Electronics/f...2rgb/calc.html

Thanks,
0perat0r
 
  


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