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Mapping the Raspberry Pi's framebuffer to memory for direct access.
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#include <stdlib.h> | |
#include <unistd.h> | |
#include <stdio.h> | |
#include <fcntl.h> | |
#include <linux/fb.h> | |
#include <sys/mman.h> | |
#include <sys/ioctl.h> | |
#include <linux/kd.h> | |
int main (int argc, char* argv[]) | |
{ | |
/* framebuffer file descriptor */ | |
int fbfd; | |
/* tty file descriptor */ | |
/* if we can't open the tty because it is not writeable then we'll | |
just leave it in text mode */ | |
int ttyfd; | |
/* structures for important fb information */ | |
struct fb_var_screeninfo vinfo; | |
struct fb_fix_screeninfo finfo; | |
/* screen size in bytes */ | |
/* x * y * bpp / 8 */ | |
unsigned long int screensize; | |
/* Pixel specification 16bpp */ | |
typedef short pixel_t; | |
/* Framebuffer pointer */ | |
typedef pixel_t* fbp_t; | |
fbp_t fbp; | |
/* Open framebuffer */ | |
fbfd = open("/dev/fb0", O_RDWR); | |
if(fbfd == -1) | |
{ | |
printf("Error: cannot open framebuffer device"); | |
exit(1); | |
} | |
/* Set the tty to graphics mode */ | |
/* Get fixed screen information */ | |
if(ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo) == -1) | |
{ | |
printf("Error reading fixed information"); | |
exit(2); | |
} | |
/* Get variable screen information */ | |
if(ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo) == -1) | |
{ | |
printf("Error reading variable information"); | |
exit(3); | |
} | |
printf("%s\n", finfo.id); | |
printf("%dx%d, %dbpp\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel); | |
screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8 ; | |
printf("%lu bytes\n", screensize); | |
fbp = (fbp_t)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); | |
} | |
/* Attempt to open the tty and set it to graphics mode */ | |
ttyfd = open("/dev/tty1", O_RDWR); | |
if (ttyfd == -1) { | |
printf("Error: could not open the tty\n"); | |
}else{ | |
ioctl(ttyfd, KDSETMODE, KD_GRAPHICS); | |
} | |
unsigned int i; | |
unsigned int num_pixels = screensize / sizeof ( pixel_t ); | |
/* Do your display logic here */ | |
for (i=0; i<num_pixels; i++) | |
{ | |
fbp[i] = i ^ fbp[i]; | |
} | |
/* Unmap the memory and release all the files */ | |
munmap(fbp, screensize); | |
if (ttyfd != -1) | |
{ | |
ioctl(ttyfd, KDSETMODE, KD_TEXT); | |
close(ttyfd); | |
} | |
close(fbfd); | |
return 0; | |
} |
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