linux驱动开发之应用程序控制LCD屏

古城微笑少年丶 2022-05-31 03:24 504阅读 0赞

1, 打开设备  
int fd = open(“/dev/fb0”, O\_RDWR);  
2, 获取到lcd屏的信息xres, yres, bpp

struct fb_var_screeninfo var;//var是容器，用来存放数据
    
            ioctl(fd, FBIOGET_VSCREENINFO, &var);//FBIOGET_VSCREENINFO表示获取可变屏幕信息，以后看到GET，一般表示拿东西，这里向驱动拿
                                |
                                .unlocked_ioctl = fb_ioctl,
                                        |
                                        struct fb_info *info = file_fb_info(file);//
                                                    |//从registered_fb数组中得到fb_info
                                                    struct fb_info *info = registered_fb[fbidx];
                                        do_fb_ioctl(info, cmd, arg);
                                            |
                                            void __user *argp = (void __user *)arg;
                                            switch (cmd) {
                                                case FBIOGET_VSCREENINFO:
                                                    var = info->var;
                                                    copy_to_user(argp, &var, sizeof(var)) ? -EFAULT : 0;
    
    
            size_t length = var.xres * var.yres * var.bits_per_pixel / 8

3,映射显存（一帧）到用户空间

//返回一个地址
             char *addr = mmap(NULL, size_t length, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
    
            framebuffer_ptr =(char *)mmap(  NULL,//如果此值为NULL,则表示用内核来自动给你分配一块虚拟空间
                                     screensize,        //空间大小
                                     PROT_READ|PROT_WRITE,//权限
                                     MAP_SHARED,        //是否可以共享
                                     framebuffer_fd,        //文件描述符
                                     0);            //从哪个地方开始

4, 得到图片数据,将数据写入到addr

/*1.打开一副图片*/
            pic_fd =open(argv[2],O_RDWR);
            printf("pic_fd=%d\n",pic_fd);
    
            /*2.获取图片大小*/
            len =lseek(pic_fd, 0, SEEK_END);//SEEK_END表示定位到一个文件的末尾
            printf("len =%ld\n",len);
    
            buffer =(char *)malloc(len);
    
            lseek(pic_fd, 0, SEEK_SET);
            /*3.读取图片数据*/
            read(pic_fd,buffer,len); 
    
            // buffer 存了bmp的图片数据, framebuffer_ptr映射之后的显存位置
            draw_bmp(buffer,(unsigned short *) framebuffer_ptr);
                |
                 bmp_read_file(bmpfilename, &bmpdata);//跳过bmp文件头
                 bmp2fb16_rgb565(bmpdata, fb);
                    |//bmp2fb16_rgb565(unsigned char *bmpdata,unsigned short *fb16)
                     fb16_buff = fb16; // fb16_buff就是framebuffer_ptr,映射之后的显存位置
                    for (y = ysize; y > 0 ; y--)
                    {
                        for (x = 0 ; x < xsize; x++) /*copy one line to frame buffer*/
                        {   
                            /*copy one pixel to frame buffer*/
                            b = *bmpdata;
                            bmpdata++;
                            b >>= 3;
                            g = *bmpdata;
                            bmpdata++;
                            g >>= 2;
                            r = *bmpdata;
                            bmpdata++;
                            r >>= 3;
                            pixel16 = (unsigned short) ((r << 11) | (g << 5) | b);  
                            *( fb16_buff +  (y* xsize + x)  ) = pixel16;//将一个像素填写到显存
                        }
                    }

程序文件：链接：[https://pan.baidu.com/s/1ggeHO1H][https_pan.baidu.com_s_1ggeHO1H] 密码：yfvz  
![这里写图片描述][SouthEast]  
lcd.test是主程序  
jpeg2bmp.o是图片数据格式的解析  
framebuffer.o是初始化framebuffer子系统  
把lcd\_test复制到指定路径中：cp lcd\_test \*.bmp /opt/rootfs/drv\_module/  
在开发板执行命令./lcd\_test /dev/fb0 logo\_girl\_800\*480.bmp  
出现以下调试信息  
![这里写图片描述][SouthEast 1]  
程序阻塞在这里，等待用户的输出（输入1显示图片，输入2显示文字）  
**附录：**  
readme.txt

1.用bmp文件 800*480
    2.注意 x,y参数 800 ,480
    unsigned int bpp    =16;
    unsigned int xsize  =800;
    unsigned int ysize  =480;
    
    在mach-smkv210.c 查看并修改.
    static struct s3c_fb_pd_win smdkv210_fb_win0 = {
        /*
        .win_mode = {
            .left_margin    = 13,
            .right_margin   = 8,
            .upper_margin   = 7,
            .lower_margin   = 5,
            .hsync_len  = 3,
            .vsync_len  = 1,
            .xres       = 800,
            .yres       = 480,
        },
        .max_bpp    = 32,
        .default_bpp    = 24,
        */
    
    
        .win_mode = {
                .left_margin       = 46,
                .right_margin   = 219,
                .upper_margin   = 23,
                .lower_margin   = 22,
                .hsync_len  = 10,
                .vsync_len  = 10,
                .xres       = 800,
                .yres       = 480,
            },
            .max_bpp    = 32,
            .default_bpp    = 16,//这是16bpp
    
    };
    
    
    3.main()中
    buffer =(char *)malloc(1152054); //不要小于bmp文件大小
    
    运行:
    [root@farsight /]# ./lcd_test /dev/fb0 logo_icer_800x480.bmp
    pic_fd=3
    len =1152054
    xres =800
    yres =480
    screensize =768000
    framebuffer_ptr is mmaped ok!
    1
    test picture!
    loadjpeg00000!!!!
    bmpread0000000!!!!
    bm2fb1600000000000!!!!
    2
    length1 =23
    length =23
    length =23

[https_pan.baidu.com_s_1ggeHO1H]: https://pan.baidu.com/s/1ggeHO1H
[SouthEast]: /images/20220531/578140eac3d647349fd72a92499e2177.png
[SouthEast 1]: /images/20220531/3b764ce28d934d05ae552207d6db6742.png