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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"><html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Qt Toolkit - Enabling the Linux framebuffer</title><style type="text/css"><!--
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<h1 align=center> Enabling the Linux framebuffer</h1><br clear="all">
<h1>How to enable framebuffer support in the Linux kernel</h1>
<p>
This is only a short guide.
See <a href="file:/usr/src/linux/README"><tt>/usr/src/linux/README</tt></a> and
<a href="file:/usr/src/linux/Documentation/fb/"><tt>/usr/src/linux/Documentation/fb/</tt></a>
for detailed information.
There is also a detailed explanation at:
<a href="http://www.linuxdoc.org/HOWTO/Framebuffer-HOWTO.html">
http://www.linuxdoc.org/HOWTO/Framebuffer-HOWTO.html</a>
<p>
<ol>
<li> Make sure that you have the Linux kernel source code in
<a href="file:/usr/src/linux/">/usr/src/linux/</a>.
<li> Log in as root and cd /usr/src/linux
<li> Configure the kernel:
<p>
Run:
<pre>
make menuconfig
</pre>
<p>
Select "Code maturity level options" and set "Prompt for
development and/or incomplete code/drivers".
<p>
Then select "Console drivers" set "Support for frame buffer
devices" to built-in (even if it says EXPERIMENTAL). Then configure
the driver. Most modern graphics cards can use the "VESA VGA
graphics console"; use that or a driver that specifically matches
your video card. Finally enable "Advanced low level driver options"
and make sure that 16 and 32 bpp packed pixel support are enabled.
<p>
When you are finished, chose exit and save.
<li> Compile the kernel
<p>
First do:
<pre>
make dep
</pre>
then:
<pre>
make bzImage
</pre>
<p>
The new kernel should now be in <tt>arch/i386/boot/bzImage</tt>
<li> Copy the kernel to the boot directory:
<pre>
cp arch/i386/boot/bzImage /boot/linux.vesafb
</pre>
<li> Edit <tt>/etc/lilo.conf</tt>
<p>
<i>
IMPORTANT: Keep a backup of /etc/lilo.conf, and have a rescue disk
available. If you make a mistake at this stage, the machine may not
boot.
</i>
<p>
The file /etc/lilo.conf specifies how the system boots. The precise
contents of the file varies from system to system, this is one example:
<pre>
boot = /dev/hda3
delay = 30
image = /boot/vmlinuz
root = /dev/hda3
label = Linux
read-only # Non-UMSDOS filesystems should be mounted read-only for checking
other=/dev/hda1
label=nt
table=/dev/hda
</pre>
<p>
<i>
IMPORTANT: Keep a backup of /etc/lilo.conf, and have a rescue disk
available. If you make a mistake here, the machine may not boot.
</i>
<p>
Make a new "image" section that is a copy of the first one, but with
image = /boot/linux.vesafb and label = Linux-vesafb. Place it just
above the first image section.
<p>
Add a line before the image section saying 'vga = 791'. (Meaning
1024x768, 16 bpp.)
<p>
With the above example, lilo.conf would now be:
<pre>
boot = /dev/hda3
delay = 30
vga = 791
image = /boot/linux.vesafb
root = /dev/hda3
label = Linux-vesafb
read-only # Non-UMSDOS filesystems should be mounted read-only for checking
image = /boot/vmlinuz
root = /dev/hda3
label = Linux
read-only # Non-UMSDOS filesystems should be mounted read-only for checking
other=/dev/hda1
label=nt
table=/dev/hda
</pre>
<p>
Do not change any lines in the file; just add new ones.
<li> Run lilo
<p>
To make the new changes take effect, run the lilo program:
<pre>
lilo
</pre>
<li> Reboot the system
<p>
You should now see a penguin logo while the system is booting.
(Or more than one on a multi-processor machine.)
<li> Error recovery
<p>
If it does not boot properly with the new kernel, you can boot with
the old kernel by entering the label of the old image section at
the LILO prompt. (with the example lilo.conf file, the old label is
Linux.)
<p>
If that does not work (probably because of an error in lilo.conf),
boot the machine using your rescue disk, restore /etc/lilo.conf from
backup and re-run lilo.
<li> Testing
<p>
Here's a short C program that opens the frame buffer and draws a
gradient-filled red square.
<pre>
<p>
int main()
{
int fbfd = 0;
struct fb_var_screeninfo vinfo;
struct fb_fix_screeninfo finfo;
long int screensize = 0;
char *fbp = 0;
int x = 0, y = 0;
long int location = 0;
<p>
// Open the file for reading and writing
fbfd = open("/dev/fb0", O_RDWR);
if (fbfd < 0) {
printf("Error: cannot open framebuffer device.\n");
exit(1);
}
printf("The framebuffer device was opened successfully.\n");
<p>
// Get fixed screen information
if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo)) {
printf("Error reading fixed information.\n");
exit(2);
}
<p>
// Get variable screen information
if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo)) {
printf("Error reading variable information.\n");
exit(3);
}
<p>
printf("%dx%d, %dbpp\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel );
<p>
// Figure out the size of the screen in bytes
screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;
<p>
// Map the device to memory
fbp = (char *)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED,
fbfd, 0);
if ((int)fbp == -1) {
printf("Error: failed to map framebuffer device to memory.\n");
exit(4);
}
printf("The framebuffer device was mapped to memory successfully.\n");
<p>
x = 100; y = 100; // Where we are going to put the pixel
<p>
// Figure out where in memory to put the pixel
for ( y = 100; y < 300; y++ )
for ( x = 100; x < 300; x++ ) {
<p>
location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +
(y+vinfo.yoffset) * finfo.line_length;
<p>
if ( vinfo.bits_per_pixel == 32 ) {
*(fbp + location) = 100; // Some blue
*(fbp + location + 1) = 15+(x-100)/2; // A little green
*(fbp + location + 2) = 200-(y-100)/5; // A lot of red
*(fbp + location + 3) = 0; // No transparency
} else { //assume 16bpp
int b = 10;
int g = (x-100)/6; // A little green
int r = 31-(y-100)/16; // A lot of red
unsigned short int t = r<<11 | g << 5 | b;
*((unsigned short int*)(fbp + location)) = t;
}
<p>
}
munmap(fbp, screensize);
close(fbfd);
return 0;
}
</pre>
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