AN2641 datasheet(26/37 Pages) STMICROELECTRONICS

26 / 37 page

Linux frame buffer

AN2641

26/37

Doc ID 14027 Rev 1

Figure 15.

A sample user application

#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);

}

// 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);

}

// Put variable screen information to Switch ON CLCD Panel

vinfo.activate |= FB_ACTIVATE_FORCE | FB_ACTIVATE_NOW;

if (ioctl(fbfd, FBIOPUT_VSCREENINFO, &vinfo)) {

printf("Error writing variable information.\n"); exit(3);

}

// 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);

}

//Loop will draw 3 color bands: blue, green and red

for ( location = 0, y = 0; y < vinfo.yres; y++ )

for ( x = 0; x < vinfo.xres; x++ ) {

if ( y < (vinfo.yres/3) )

{

*(fbp + location) = 0xFF;//show Blue

*(fbp + location+1) = 0;//no Green

*(fbp + location+2) = 0;//no Red

*(fbp + location+3) = 0;//No Transparency

}

else if ( y < (2*vinfo.yres/3) )

{

*(fbp + location) = 0xFF;// no Blue

*(fbp + location + 1) = 0;// show Green

*(fbp + location + 2) = 0;// no Red

*(fbp + location + 3) = 0;// No transparency

}

else

{

*(fbp + location) = 0;// no Blue

*(fbp + location + 1) = 0; // no Green

*(fbp + location + 2) = 0xFF;// show Red

*(fbp + location + 3) = 0;// No transparency

}

location +=4;

}

munmap(fbp, screensize);

close(fbfd);

return 0;

}

AN2641 Datasheet(PDF) 26 Page - STMicroelectronics

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