我是靠谱客的博主 内向绿草,这篇文章主要介绍一个简单的framebuffer的显示使用例子,现在分享给大家,希望可以做个参考。

    本例子中,显示设备是一个oled的显示屏; 没有过多的关于分辨率,刷新频率的设置; 只是演示一个framebuffer的例子。

一, kernel层的驱动代码如下:

    1. 注册,这是一个使用i2c通讯的显示设备,因此注册成一个i2c设备。

          定义:

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struct ssd1307fb_par { struct i2c_client *client; u32 height; struct fb_info *info; struct ssd1307fb_ops *ops; u32 page_offset; struct pwm_device *pwm; u32 pwm_period; int reset; int bklight; u32 width; };

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static const struct i2c_device_id ssd1307fb_i2c_id[] = { { "ssd1305fb", 0 }, { "ssd1306fb", 0 }, { "ssd1307fb", 0 }, { } }; MODULE_DEVICE_TABLE(i2c, ssd1307fb_i2c_id); static struct i2c_driver ssd1307fb_driver = { .probe = ssd1307fb_probe, .remove = ssd1307fb_remove, .suspend = ssd1307fb_suspend, .resume = ssd1307fb_resume, .id_table = ssd1307fb_i2c_id, .driver = { .name = "ssd1307fb", .of_match_table = ssd1307fb_of_match, .owner = THIS_MODULE, }, }; module_i2c_driver(ssd1307fb_driver);

     2. 正常启动后进入probe() 函数, 进行初始化,包括变量的初始化,显示器件寄存器的初始化,和framebuffer的初始化等; 我们只列举关于framebuffer的初始化。

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struct fb_info *info; struct device_node *node = client->dev.of_node; u32 vmem_size; struct ssd1307fb_par *par; u8 *vmem; int ret;

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info = framebuffer_alloc(sizeof(struct ssd1307fb_par), &client->dev); if (!info) { dev_err(&client->dev, "Couldn't allocate framebuffer.n"); return -ENOMEM; }
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par->ops = (struct ssd1307fb_ops *)of_match_device(ssd1307fb_of_match, &client->dev)->data;

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vmem_size = par->width * par->height / 8; vmem = vmalloc(vmem_size); if (!vmem) { dev_err(&client->dev, "Couldn't allocate graphical memory.n"); ret = -ENOMEM; goto fb_alloc_error; } info->fbops = &ssd1307fb_ops; info->fix = ssd1307fb_fix; info->fix.line_length = par->width / 8; info->fbdefio = &ssd1307fb_defio;

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info->var = ssd1307fb_var; info->var.xres = par->width; info->var.xres_virtual = par->width; info->var.yres = par->height; info->var.yres_virtual = par->height; info->var.red.length = 1; info->var.red.offset = 0; info->var.green.length = 1; info->var.green.offset = 0; info->var.blue.length = 1; info->var.blue.offset = 0; info->screen_base = (char *)vmem; info->fix.smem_start = (unsigned long)vmem; info->fix.smem_len = vmem_size; fb_deferred_io_init(info);
       //   以上是对 info 变量的初始化,在我们的例子里,有一些,未必用到;

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memcpy(vmem, picture1, vmem_size); ssd1305fb_update_display(par); dev_info(&client->dev, "%s: have update displayn", __func__); ret = register_framebuffer(info); if (ret) { dev_err(&client->dev, "Couldn't register the framebuffern"); goto panel_init_error; }
       //  上面是对共享内存的初始化和, 进行framebuffer的注册。

       //  在上面的注册中, 一些文件系统的定义如下:

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static struct fb_ops ssd1307fb_ops = { .owner = THIS_MODULE, .fb_read = fb_sys_read, .fb_write = ssd1307fb_write, .fb_fillrect = ssd1307fb_fillrect, .fb_copyarea = ssd1307fb_copyarea, .fb_imageblit = ssd1307fb_imageblit, };

        //   在上面的文件ops注册中, 虽然定义了 fb_read 和 fb_write 等文件节点,但在我们的例子中,这几个节点都没有用到。我们使用的是下面的 fb_deferred_io 的结构。
        //  在下面中, ssd1307fb_ssd1305_init  函数会被自动调用,进行oled显示设备的初始化。

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static struct ssd1307fb_ops ssd1307fb_ssd1305_ops = { .init = ssd1307fb_ssd1305_init, }; static struct ssd1307fb_ops ssd1307fb_ssd1306_ops = { .init = ssd1307fb_ssd1306_init, }; static const struct of_device_id ssd1307fb_of_match[] = { { .compatible = "solomon,ssd1305fb-i2c", .data = (void *)&ssd1307fb_ssd1305_ops, }, { .compatible = "solomon,ssd1306fb-i2c", .data = (void *)&ssd1307fb_ssd1306_ops, }, { .compatible = "solomon,ssd1307fb-i2c", .data = (void *)&ssd1307fb_ssd1307_ops, }, {}, }; MODULE_DEVICE_TABLE(of, ssd1307fb_of_match);

       //   针对共享内存的buff的初始化,如下:

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static void ssd1307fb_deferred_io(struct fb_info *info, struct list_head *pagelist) { ssd1305fb_update_display(info->par); } static struct fb_deferred_io ssd1307fb_defio = { .delay = HZ, .deferred_io = ssd1307fb_deferred_io, };

       //    这样,当应用层更改共享内存的数据时,则 ssd1307fb_deferred_io()  函数会自动被调用; 从而调用ssd1305fb_update_display()函数,进行显示的刷新。


二、 应用层的调用例子:

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#include <unistd.h> #include <stdio.h> #include <string.h> #include <fcntl.h> #include <linux/fb.h> #include <sys/mman.h> #define SSD1307FB_SSD1305_MAX_COL 128 #define SSD1307FB_SSD1305_MAX_ROW 64

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unsigned char picture5[SSD1307FB_SSD1305_MAX_ROW/8][SSD1307FB_SSD1305_MAX_COL]={ 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, ... ...

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int main() { int fbfd = 0; struct fb_var_screeninfo vinfo; struct fb_fix_screeninfo finfo; long int screensize = 0; char *fbp = 0; // Open the file for reading and writing fbfd = open("/dev/graphics/fb3", O_RDWR); if (fbfd < 0) { printf("Error: cannot open framebuffer device.n"); exit(1); } printf("The framebuffer device was opened successfully. fbfd=%xn", fbfd); screensize = 128 * 8; printf("the screensize is %dn", screensize ); // 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); } printf("The framebuffer device was mapped to memory successfully.n"); memcpy(fbp, picture5, screensize); munmap(fbp, screensize); close(fbfd); return 0; }



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