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/*! \page emb-framebuffer-howto.html

\title Enabling the Linux Framebuffer

This is only a short guide.
See \l file:/usr/src/linux/README and
\l file:/usr/src/linux/Documentation/fb/ for detailed information.
There is also a detailed explanation at
\l http://www.linuxdoc.org/HOWTO/Framebuffer-HOWTO.html.

\list 1
\i Make sure that you have the Linux kernel source code in
\l file:/usr/src/linux/.

\i Log in as root and \c cd \c /usr/src/linux

\i Configure the kernel:
   
   Run:
\code
    make menuconfig
\endcode

   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.

\i Compile the kernel

   First do:
\code
    make dep
\endcode
   then:
\code
    make bzImage
\endcode

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

\i Copy the kernel to the boot directory:
\code
    cp arch/i386/boot/bzImage /boot/linux.vesafb
\endcode

\i 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, this is one example:
\code
# 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
\endcode

  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:
\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
\endcode

Do not change any existing lines in the file; just add new ones.

\i To make the new changes take effect, run the lilo program:
\code
    lilo
\endcode

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

\i 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.

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

\code
#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;
}
\endcode
\endlist

*/