Date: Fri, 01 Sep 2000 16:03:11 +0200 From: Siegbert Baude <siegbert.baude@gmx.de> To: Ignacio Zelaya <izelaya@infovia.com.ar>, "freebsd-questions@freebsd.org" <freebsd-questions@freebsd.org> Subject: Re: TextClockFreq = ?????? Message-ID: <39AFB71F.129192BE@gmx.de> References: <39AE8443.FD9900D4@infovia.com.ar>
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Hi Ignacio, > But i dont know how to obtain my normal dot clock freq. > when the text console is working fine, so i can make > a coorrect entrie in TextClockFreq in the XF86Config file. > > The only i culd know is from monitor menu, is the text mode > is running in: > 31,5KHz / 70Hz 720x400. > > But maths fails here for me. > > 31,5KHz x 720 x 1.3 ~= 29.484 Mhz dot ??? Your number of visual lines is 400 not 720. From your monitor output you get: 31,5 kHz (number of lines per second) 70 Hz (number of complete screen refreshs per second). A normal text mode line should look like: # 640x400 @ 70 Hz, 31.5 kHz hsync Modeline "640x400" 25.175 640 664 760 800 400 409 411 450 Taken from my XF86Config. So your dot clock will be 25.175 MHz . 800 total ticks per line, 450 total lines per screen. That is a vertical refresh rate of 25.175MHz/(800*450)=70Hz . Bingo Your horizontal line rate is 25.175MHz/800=31.5kHz . Bingo again What happens exactly: your line is 800 ticks long. The first 640 ticks are used for visual information. (664-640)ticks there will be nothing, (760-664)ticks there will be a sync signal (telling the monitor to reposition the beam to the next line), (800-760)ticks the beam will reposition. Same scheme for the lines: your screen is 450 lines long. The first 400 lines are used for visual information. (409-400)lines there will be nothing, (411-409)lines there will be a sync signal (telling the monitor to reposition the beam to the top of the screen), (450-411)lines the beam will reposition. The time needed for the gap, synch and reposition phases is monitor dependent, but roughly the same for all modes a monitor is capable of doing. Standard VESA modes should be applicable for all modern monitors. So if you want to switch to a different resolution with a different dot clock, you have to arrange your ticks to rebuild the correct lengths of these phases. (if you will find any numbers in your monitorīs handbook, it will be no ticks, but those lengths - something in the microsecond area, the term "porch" should appear nearby; but this piece of information is very rarely to find. :-( IMHO itīs a design fault within the XF86Config file to urge the user to calculate the ticks. There should be only the necessity to define the sync pulse timing once for all modes. For deeper explanation of these things look at: http://www.linux.org/docs/ldp/howto/XFree86-Video-Timings-HOWTO.html Hope this helps Siegbert To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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