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This is only a short guide. See /usr/src/linux/README and /usr/src/linux/Documentation/fb/ for detailed information. There is also a detailed explanation at http://www.linuxdoc.org/HOWTO/Framebuffer-HOWTO.html.
Run:
make menuconfig
Select "Code maturity level options" and set "Prompt for development and/or incomplete code/drivers".
Then select "Console drivers" and 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.
When you are finished, chose exit and save.
First do:
make dep
then:
make bzImage
The new kernel should now be in arch/i386/boot/bzImage.
cp arch/i386/boot/bzImage /boot/linux.vesafb
Warning: Keep a backup of /etc/lilo.conf, and have a rescue disk available. If you make a mistake, the machine may not boot.
The file /etc/lilo.conf specifies how the system boots. The precise contents of the file varies from system to system. Here is an example:
# LILO configuration file
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
Make a new "image" section that is a copy of the first one, but with
image = /boot/linux.vesafband
label = Linux-vesafb
endcode
Place it just above the first image section.
Add a line before the image section saying \c{vga = 791}. (Meaning
1024x768, 16 bpp.)
With the above example, lilo.conf would now be:
\code
# LILO configuration file
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
Do not change any existing lines in the file; just add new ones.
lilo
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.
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <sys/mman.h>
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;
// Open the file for reading and writing
fbfd = open("/dev/fb0", O_RDWR);
if (!fbfd) {
printf("Error: cannot open framebuffer device.\n");
exit(1);
}
printf("The framebuffer device was opened successfully.\n");
// Get fixed screen information
if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo)) {
printf("Error reading fixed information.\n");
exit(2);
}
// Get variable screen information
if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo)) {
printf("Error reading variable information.\n");
exit(3);
}
printf("%dx%d, %dbpp\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel );
// Figure out the size of the screen in bytes
screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;
// 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");
x = 100; y = 100; // Where we are going to put the pixel
// Figure out where in memory to put the pixel
for ( y = 100; y < 300; y++ )
for ( x = 100; x < 300; x++ ) {
location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +
(y+vinfo.yoffset) * finfo.line_length;
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;
}
}
munmap(fbp, screensize);
close(fbfd);
return 0;
}
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