cat /dev/fb0 > screen.img - получить raw экрана
cat screen.img > /dev/fb0  - отобразить на экране

#include <stdio.h>
#include <stdlib.h>
int
main(int argc, char *argv[])
{
FILE * data;
int i,x,y;
data = fopen("/dev/fb0","w");
for(y=0;y<480;y++);
{
   for(x=0;x<800;x++);
   {
     fputc(0xff,data);
   }
}
fclose(data);
return 0;
}

ls -l /dev/fb*
lrwxrwxrwx  1 root root 4 2007-09-27 13:05 /dev/fb0 -> fb/0
ls -l /dev/fb/0
crw-rw----  1 root video 29, 0 2007-09-27 13:05 /dev/fb/0

pxa2xx-fb pxa2xx-fb: overriding resolution: 800x480
pxa2xx-fb pxa2xx-fb: overriding bit depth: 18
pxa2xx-fb pxa2xx-fb: override pixclock: 30000
pxa2xx-fb pxa2xx-fb: override left: 1
pxa2xx-fb pxa2xx-fb: override right: 1
pxa2xx-fb pxa2xx-fb: override vsynclen: 10
PXA: invalid hsync_len 0
PXA: invalid hsync_len 0
Console: switching to colour frame buffer device 100x60

#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, %d linelen %d xoffs %d yoffs\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel,\
    finfo.line_length,vinfo.xoffset,vinfo.yoffset);

        // 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");
        for (y = 0; y < 360; y++)
            for (x = 0; x < 800; x++) {
                location = (x+vinfo.xoffset) * 3 + (y+vinfo.yoffset) * finfo.line_length;
                    int b = 0x0;
                    int g = 0x0;     // A little green
                    int r = 0x00;    // A lot of red
                    unsigned int t = r<<12 | g << 6 | b;
                    *((unsigned  char*)(fbp + location)) = t&0xff;
                    *((unsigned  char*)(fbp + location + 1)) = (t>>8)&0xff;
                    *((unsigned  char*)(fbp + location + 2)) = (t>>16)&0xff;

            }
        // Figure out where in memory to put the pixel
        for (y = 10; y < 300; y++)
            for (x = 100; x < 200; x++) {
                location = (x+vinfo.xoffset) * 3 + (y+vinfo.yoffset) * finfo.line_length;
                    int b = 0x00;
                    int g = 0xff;     // A little green
                    int r = 0x00;    // A lot of red
                    unsigned  int t = r<<12 | g << 6 | b;
                    *((unsigned  char*)(fbp + location)) = t&0xff;
                    *((unsigned  char*)(fbp + location + 1)) = (t>>8)&0xff;
                    *((unsigned  char*)(fbp + location + 2)) = (t>>16)&0xff;
            }
        x = 400; y = 100;       // Where we are going to put the pixel
        for (y = 10; y < 200; y++)
            for (x = 300; x < 400; x++) {
                location = (x+vinfo.xoffset) * 3 + (y+vinfo.yoffset) * finfo.line_length;
                    int b = 0x0;
                    int g = 0x00;     // A little green
                    int r = 0xff;    // A lot of red
                    unsigned  int t = r<<12 | g << 6 | b;
                    *((unsigned  char*)(fbp + location)) = t&0xff;
                    *((unsigned  char*)(fbp + location + 1)) = (t>>8)&0xff;
                    *((unsigned  char*)(fbp + location + 2)) = (t>>16)&0xff;
            }
        for (y = 10; y < 360; y++)
            for (x = 500; x < 885; x++) {
                location = (x+vinfo.xoffset) * 3 + (y+vinfo.yoffset) * finfo.line_length;
                    int b = 0xff;
                    int g = 0x0;     // A little green
                    int r = 0x00;    // A lot of red
                    unsigned int t = r<<12 | g << 6 | b;
                    *((unsigned  char*)(fbp + location)) = t&0xff;
                    *((unsigned  char*)(fbp + location + 1)) = (t>>8)&0xff;
                    *((unsigned  char*)(fbp + location + 2)) = (t>>16)&0xff;
            }
        munmap(fbp, screensize);
        close(fbfd);
        return 0;
    }

reg.screensize = info->var.xres | (info->var.yres << 12);