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Enabling the Linux Framebuffer

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.

Make sure that you have the Linux kernel source code in /usr/src/linux/.
Log in as root and cd /usr/src/linux
Configure the kernel:
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.
Compile the kernel
First do:
```
    make dep
```
then:
```
    make bzImage
```
The new kernel should now be in arch/i386/boot/bzImage.

Copy the kernel to the boot directory:

    cp arch/i386/boot/bzImage /boot/linux.vesafb

Edit /etc/lilo.conf.

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.vesafb

and

      label = Linux-vesafb

Place it just above the first image section.

Add a line before the image section saying vga = 791. (Meaning 1024x768, 16 bpp.)

With the above example, lilo.conf would now be:

    # 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.

To make the new changes take effect, run the lilo program:
```
        lilo
```
Reboot the system. You should now see a penguin logo while the system is booting. (Or more than one on a multi-processor machine.)
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.)
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.

Testing: Here's a short program that opens the frame buffer and draws a gradient-filled red square.

    #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;
    }

Trademarks

Qt 4.1.0