HomeHome

Enabling the Linux framebuffer


How to enable framebuffer support in the Linux kernel

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

  1. Make sure that you have the Linux kernel source code in /usr/src/linux/.
  2. Log in as root and cd /usr/src/linux
  3. 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" 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.

  4. Compile the kernel

    First do:

            make dep
    
    then:
            make bzImage
    

    The new kernel should now be in arch/i386/boot/bzImage

  5. Copy the kernel to the boot directory:
            cp arch/i386/boot/bzImage /boot/linux.vesafb
    
  6. Edit /etc/lilo.conf

    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.

    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:

    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
    

    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.

    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:

    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 lines in the file; just add new ones.

  7. Run lilo

    To make the new changes take effect, run the lilo program:

            lilo
    
  8. Reboot the system

    You should now see a penguin logo while the system is booting. (Or more than one on a multi-processor machine.)

  9. Error recovery

    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.

  10. Testing

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

    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 < 0) { 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; }


    Copyright © 2005 TrolltechTrademarks
    Qt version 2.3.10