<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> <HTML> <HEAD> <META NAME="GENERATOR" CONTENT="SGML-Tools 1.0.9"> <TITLE>Framebuffer HOWTO: How do I convert XFree86 mode-lines into framebuffer device timings?</TITLE> <LINK HREF="Framebuffer-HOWTO-19.html" REL=next> <LINK HREF="Framebuffer-HOWTO-17.html" REL=previous> <LINK HREF="Framebuffer-HOWTO.html#toc18" REL=contents> </HEAD> <BODY> <A HREF="Framebuffer-HOWTO-19.html">Next</A> <A HREF="Framebuffer-HOWTO-17.html">Previous</A> <A HREF="Framebuffer-HOWTO.html#toc18">Contents</A> <HR> <H2><A NAME="s18">18. How do I convert XFree86 mode-lines into framebuffer device timings?</A></H2> <P> <P>If you have XFree86 (X11) installed on your machine, and you can use it successfully, it is a simple matter to convert the mode-lines in your XF86Config to the required timings needed by the framebuffer devices. <P>The framebuffer device requires the following fields <UL> <LI>pixclock - pixel clock in pico seconds</LI> <LI>left_margin - time fron sync to picture</LI> <LI>right_margin - time from picture to sync</LI> <LI>upper_margin - time from sync to picture</LI> <LI>lower_margin - time from picture to sync</LI> <LI>hsync_len - length of horizontal sync</LI> <LI>vsync_len - length of vertical sync</LI> </UL> <P> <P>An XFree86 mode line has the following fields <P> <PRE> Modeline "1280x1024" DCF HR SH1 SH2 HFL VR SV1 SV2 VFL </PRE> <P> <P>It is necessary to do some simple calculations to translate the XF86 mode-lines into a set of framebuffer device timings. As an example, we shall examine how to convert a mode-line taken from my XF86Config file. <P> <PRE> Modeline "1280x1024" 110.00 1280 1328 1512 1712 1024 1025 1028 1054 </PRE> <P> <P>First, calculate the required pixclock rate. XFree86 uses megahertz whilst framebuffer devices uses picoseconds (Why, I don't know). Divide one million by DCF. For example, 1,000,000 / 110.0 = 9090.9091 <P> <P>Now we need to calculate the horizontal timings. <UL> <LI>left_margin = HFL - SH2 </LI> <LI>right_margin = SH1 - HR</LI> <LI>hsync_len = SH2 - SH1</LI> </UL> <P> <P>In our example, this would be: <UL> <LI>left_margin = 1712 - 1512 = 200</LI> <LI>right_margin = 1328 - 1280 = 48</LI> <LI>hsync_len = 1512 - 1328 = 184</LI> </UL> <P> <P>And now we need to calculate the vertical timings. <UL> <LI>upper_margin = VFL - SV2</LI> <LI>lower_margin = SV1 - VR</LI> <LI>vsync_len = SV2 - SV1</LI> </UL> <P> <P>For our example, this would be: <UL> <LI>upper_margin = 1054 - 1028 = 26</LI> <LI>lower_margin = 1025 - 1024 = 1</LI> <LI>vsync_len = 1028 - 1025 = 3</LI> </UL> <P> <P>Now we can use this information to set up the framebuffer for the desired mode. For example, for the matroxfb framebuffer, it requires: <P> <PRE> video=matrox:xres:<>,yres:<>,depth:<>,left:<>,right:<>,hslen:<>,upper:<>,lower:<>,vslen:<> </PRE> <P>I put in my /etc/lilo.conf the following line: <PRE> append = "video=matrox:xres:1280,yres:1024,depth:32,left:200,right:48,hslen:184,upper:26,lower:0,vslen:3" </PRE> <P> <P>Note that in this case the pixclock isn't used. It's only necessary if you don't like the default pixclock rates. You can supply this as a parameter as well. Setting the pixclock is documented in other parts of this HOWTO. <P> <HR> <A HREF="Framebuffer-HOWTO-19.html">Next</A> <A HREF="Framebuffer-HOWTO-17.html">Previous</A> <A HREF="Framebuffer-HOWTO.html#toc18">Contents</A> </BODY> </HTML>
