LCD 应用程序

#include<unistd.h>
#include <stdlib.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

    //FBIOGET_FSCREENINFO获得固定的屏幕参数设置

    if (ioctl(fbfd, FBIOGET_FSCREENINFO,&finfo)){
        printf("Error reading fixed information.\n");
        exit(2);
    }

    printf("%d, %d, %d, %d\n", finfo.smem_start, finfo.smem_len, finfo.mmio_start,finfo.mmio_len);
    //869007360, 153600, 0, 0

    // Get variable screen information

    //FBIOGET_VSCREENINFO 获得可变的屏幕参数

    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);
    //320X240,16bpp bpp 每像素位数 每个点用多少个字节表示


    // Figure out the size of the screen in bytes

     screensize = vinfo.xres* vinfo.yres * vinfo.bits_per_pixel / 8;
    //2^16=64K TFT 320*240*16/8=153600byte


    // Map the device to memory

    /*void *mmap(void *start, size_t length, int prot, int flags,
　　int fd, off_t offset);mmap函数是unix/linux下的系统调用
     fbmem.c是内核的，应用程序调用了mmap进入内核空间就是执行的fb_mmap了，
     应用程序是统一的接口，但是在内核空间，不同的驱动使用的实现函数是不一样的*/
    //#include <unistd.h> and #include <sys/mman.h> /usr/include/sys/mman.h

     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");
#if 1
     x = 10; y = 10; // Where we are going to put the pixel


    // Figure out where in memory to put the pixel

    for (y = 10; y < 20; y++)
        for (x = 10; x < 30; x++)
        {
             location = (x+vinfo.xoffset)* (vinfo.bits_per_pixel/8)+
                       (y+vinfo.yoffset)* finfo.line_length;

            if (vinfo.bits_per_pixel== 32)
            {
                *(fbp+ location) = 10; // Some blue

                *(fbp+ location + 1)= 15+(x-10)/2;// A little green

                *(fbp+ location + 2)= 20-(y-10)/5;// A lot of red

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

            }
            else
            { //assume 16bpp

                unsigned short b = 10;
                unsigned short g = (x-10)/6;// A little green

                unsigned short r = 31-(y-10)/16;// A lot of red

                unsigned short t = r<<11| g << 5| b;
                *((unsignedshort *)(fbp+ location))= t;
    //     printf("x=%d,%d\n",x,y);

            }
        }
#endif
     munmap(fbp, screensize);//删除特定地址区域的对象映射 int munmap(void *start, size_t length);

    printf("The framebuffer device was munmapped to memory successfully.\n");
    close(fbfd);
    printf("The framebuffer device was closed successfully.\n");
    return 0;
}