Hello.
I am trying to test linux frame buffer on the ubuntu 18.04 installed aio-3399j board.
On the console,
# cat /dev/urandom > /dev/fb0
Testing with this command works fine. (noise displayed on the screen)
However, when I test frame buffer with c code using mmap(), it fails.
(mmap returns -1 (EINVAL))
# ./fb
The framebuffer device was opened successfully.
1280x800, 32bpp
Error: failed to map framebuffer device to memory: Invalid argument
Can anyone help me to solve this problem?
c source code:
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <sys/mman.h>
#include <sys/ioctl.h>
int main(int argc, char *argv)
{
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 == -1)
{
perror("Error: cannot open framebuffer device");
exit(1);
}
printf("The framebuffer device was opened successfully.\n");
// Get fixed screen information
if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo) == -1)
{
perror("Error reading fixed information");
exit(2);
}
// Get variable screen information
if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo) == -1)
{
perror("Error reading variable information");
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)
{
perror("Error: failed to map framebuffer device to memory");
exit(4);
}
printf("The framebuffer device was mapped to memory successfully.\n");
x = 300;
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;
}