在前面的LED驱动控制中，都只使用了一个设备节点（一个次设备号）来进行操作，本例来讨论一下如何把三个基色的LED分别当成三个次设备，即产生出三个设备节点文件，但共用一个设备驱动（同一个主设备号），应用程序各自控制各自的LED 。
下面先给出完整的驱动程序代码，文件名仍为led.c。
#include <linux/init.h> #include <linux/module.h> #include <linux/cdev.h> #include <linux/fs.h> #include <linux/uaccess.h> #include <linux/io.h> //以下定义总线及寄存器的物理地址 #define CCM_BASE_ADDR (0x20C4000) #define CCM_CCGR1_ADDR (CCM_BASE_ADDR + 0x6C) #define CCM_CCGR2_ADDR (CCM_BASE_ADDR + 0x70) #define CCM_CCGR3_ADDR (CCM_BASE_ADDR + 0x74) #define GPIO1_BASE_ADDR (0x209C000) #define GPIO1_DR_ADDR (GPIO1_BASE_ADDR + 0x0000) #define GPIO1_GDIR_ADDR (GPIO1_BASE_ADDR + 0x0004) #define GPIO1_PSR_ADDR (GPIOB_BASE_ADDR + 0x0008) #define GPIO4_BASE_ADDR (0x20A8000) #define GPIO4_DR_ADDR (GPIO4_BASE_ADDR + 0x0000) #define GPIO4_GDIR_ADDR (GPIO4_BASE_ADDR + 0x0004) #define GPIO4_PSR_ADDR (GPIOC_BASE_ADDR + 0x0008) #define SW_MUX_CTL_ADDR (0x20E0000) #define IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO04_ADDR (SW_MUX_CTL_ADDR + 0x6C) #define IOMUXC_SW_MUX_CTL_PAD_CSI_HSYNC_ADDR (SW_MUX_CTL_ADDR + 0x1E0) #define IOMUXC_SW_MUX_CTL_PAD_CSI_VSYNC_ADDR (SW_MUX_CTL_ADDR + 0x1DC) #define IOMUXC_SW_PAD_CTL_PAD_GPIO1_IO04_ADDR (SW_MUX_CTL_ADDR + 0x2F8) #define IOMUXC_SW_PAD_CTL_PAD_CSI_HSYNC_ADDR (SW_MUX_CTL_ADDR + 0x46C) #define IOMUXC_SW_PAD_CTL_PAD_CSI_VSYNC_ADDR (SW_MUX_CTL_ADDR + 0x468) //以下定义时钟控制寄存器名称 static void __iomem *CCM_CCGR1; static void __iomem *CCM_CCGR3; static void __iomem *IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO04; static void __iomem *IOMUXC_SW_PAD_CTL_PAD_GPIO1_IO04; static void __iomem *IOMUXC_SW_MUX_CTL_PAD_CSI_HSYNC; static void __iomem *IOMUXC_SW_PAD_CTL_PAD_CSI_HSYNC; static void __iomem *IOMUXC_SW_MUX_CTL_PAD_CSI_VSYNC; static void __iomem *IOMUXC_SW_PAD_CTL_PAD_CSI_VSYNC; static void __iomem *GPIO1_GDIR; static void __iomem *GPIO1_DR; static void __iomem *GPIO4_GDIR; static void __iomem *GPIO4_DR; dev_t devid; //设备号 struct cdev chrdev[3]; //字符设备结构体数组 struct class *class; //类结构体 struct device *device; //设备结构体 //实现open函数，为file_oprations结构体成员函数 static int led_open(struct inode *inode, struct file *filp) { unsigned int tmp;//以下使能GPIO1、GPIO4的端口时钟tmp = ioread32(CCM_CCGR1);tmp |= 0xC000000;iowrite32(tmp, CCM_CCGR1);tmp = ioread32(CCM_CCGR3);tmp |= 0x3000;iowrite32(tmp, CCM_CCGR3);return 0; } //实现write函数，为file_oprations结构体成员函数 static ssize_t led_write(struct file *filp, const char __user *buf, size_t cnt, loff_t *offt) {unsigned char value;unsigned int tmp;unsigned long n;unsigned int minor;minor = iminor(file_inode(filp)); //获取次设备号n = copy_from_user(&value, buf, cnt); //从应用空间获取值 switch(minor){case 0: //次设备号0表示红色LEDif(value){ //熄灭红色LEDtmp = ioread32(GPIO1_DR);tmp |= (1<<4);iowrite32(tmp, GPIO1_DR);}else{ //点亮红色LEDtmp = ioread32(GPIO1_DR);tmp &= ~(1<<4);iowrite32(tmp, GPIO1_DR);}break;case 1: //次设备号1表示绿色LEDif(value){ //熄灭绿色LEDtmp = ioread32(GPIO4_DR);tmp |= (1<<20);iowrite32(tmp, GPIO4_DR);}else{ //点亮绿色LEDtmp = ioread32(GPIO4_DR);tmp &= ~(1<<20);iowrite32(tmp, GPIO4_DR);}break;case 2: //次设备号2表示蓝色LEDif(value){ //熄灭蓝色LEDtmp = ioread32(GPIO4_DR);tmp |= (1<<19);iowrite32(tmp, GPIO4_DR);}else{ //点亮蓝色LEDtmp = ioread32(GPIO4_DR);tmp &= ~(1<<19);iowrite32(tmp, GPIO4_DR);}default:break;}return cnt; } //实现release函数，为file_oprations结构体函数 static int led_release(struct inode *inode, struct file *filp) {unsigned int tmp;//以下禁止GPIO1、GPIO4的端口时钟tmp = ioread32(CCM_CCGR1);tmp &= ~0xC000000;iowrite32(tmp, CCM_CCGR1);tmp = ioread32(CCM_CCGR3);tmp &= ~0x3000;iowrite32(tmp, CCM_CCGR3);return 0; } //填充一个file_oprations类型的结构体，名为led_dev_fops，包含上述声明的成员函数 static struct file_operations led_dev_fops = {.owner = THIS_MODULE,.open = led_open, //指定open函数成员.write = led_write, //指定write函数成员.release = led_release, //指定release函数成员 }; //初始化函数，此处为驱动模块的入口函数 static int __init led_init(void) {unsigned int tmp;dev_t cur_id;//以下实现各个寄存器的地址映射CCM_CCGR1 = ioremap(CCM_CCGR1_ADDR, 4);CCM_CCGR3 = ioremap(CCM_CCGR3_ADDR, 4);IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO04 = ioremap(IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO04_ADDR, 4);IOMUXC_SW_MUX_CTL_PAD_CSI_HSYNC = ioremap(IOMUXC_SW_MUX_CTL_PAD_CSI_HSYNC_ADDR, 4);IOMUXC_SW_MUX_CTL_PAD_CSI_VSYNC = ioremap(IOMUXC_SW_MUX_CTL_PAD_CSI_VSYNC_ADDR, 4);IOMUXC_SW_PAD_CTL_PAD_GPIO1_IO04 = ioremap(IOMUXC_SW_PAD_CTL_PAD_GPIO1_IO04_ADDR, 4);IOMUXC_SW_PAD_CTL_PAD_CSI_HSYNC = ioremap(IOMUXC_SW_PAD_CTL_PAD_CSI_HSYNC_ADDR, 4);IOMUXC_SW_PAD_CTL_PAD_CSI_VSYNC = ioremap(IOMUXC_SW_PAD_CTL_PAD_CSI_VSYNC_ADDR, 4);GPIO1_GDIR = ioremap(GPIO1_GDIR_ADDR, 4);GPIO4_GDIR = ioremap(GPIO4_GDIR_ADDR, 4);GPIO1_DR = ioremap(GPIO1_DR_ADDR, 4);GPIO4_DR = ioremap(GPIO4_DR_ADDR, 4);//以下使能GPIO1、GPIO4的端口时钟tmp = ioread32(CCM_CCGR1);tmp |= 0xC000000;iowrite32(tmp, CCM_CCGR1);tmp = ioread32(CCM_CCGR3);tmp |= 0x3000;iowrite32(tmp, CCM_CCGR3);//以下把GPIO1_4、GPIO4_19、GPIO4_20端口配置为GPIO模式tmp = ioread32(IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO04);tmp = 0x05;iowrite32(tmp, IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO04);tmp = ioread32(IOMUXC_SW_MUX_CTL_PAD_CSI_HSYNC);tmp = 0x05;iowrite32(tmp, IOMUXC_SW_MUX_CTL_PAD_CSI_HSYNC);tmp = ioread32(IOMUXC_SW_MUX_CTL_PAD_CSI_VSYNC);tmp = 0x05;iowrite32(tmp, IOMUXC_SW_MUX_CTL_PAD_CSI_VSYNC);//以下把GPIO1_4、GPIO4_19、GPIO4_20端口配置为上拉、低速、等模式tmp = ioread32(IOMUXC_SW_PAD_CTL_PAD_GPIO1_IO04);tmp = 0xF838;iowrite32(tmp, IOMUXC_SW_PAD_CTL_PAD_GPIO1_IO04);tmp = ioread32(IOMUXC_SW_PAD_CTL_PAD_CSI_HSYNC);tmp = 0xF838;iowrite32(tmp, IOMUXC_SW_PAD_CTL_PAD_CSI_HSYNC);tmp = ioread32(IOMUXC_SW_PAD_CTL_PAD_CSI_VSYNC);tmp = 0xF838;iowrite32(tmp, IOMUXC_SW_PAD_CTL_PAD_CSI_VSYNC);//以下把GPIO1_4、GPIO4_19、GPIO4_20端口配置为输出tmp = ioread32(GPIO1_GDIR);tmp |= 0x10;iowrite32(tmp, GPIO1_GDIR);tmp = ioread32(GPIO4_GDIR);tmp |= 0x180000;iowrite32(tmp, GPIO4_GDIR);//以下设定GPIO1_4、GPIO4_19、GPIO4_20端口的初始值tmp = ioread32(GPIO1_DR);tmp |= (1<<4);iowrite32(tmp, GPIO1_DR);tmp = ioread32(GPIO4_DR);tmp |= (1<<20 | 1<<19);iowrite32(tmp, GPIO4_DR);//以下禁止GPIO1、GPIO4的端口时钟tmp = ioread32(CCM_CCGR1);tmp &= ~0xC000000;iowrite32(tmp, CCM_CCGR1);tmp = ioread32(CCM_CCGR3);tmp &= ~0x3000;iowrite32(tmp, CCM_CCGR3);//申请主设备号if(alloc_chrdev_region(&devid, 0, 1, "led") < 0){printk("Couldn't alloc_chrdev_region!\r\n");return -EFAULT;}//创建类 class = class_create(THIS_MODULE, "led_dev");//以下实现三个字符型设备的申请和注册及创建三个设备节点for (tmp=0; tmp < 3; tmp++) {chrdev[tmp].owner = THIS_MODULE;//绑定前面声明的file_oprations类型的结构体到字符设备cdev_init(&chrdev[tmp], &led_dev_fops);cur_id = MKDEV(MAJOR(devid), MINOR(devid) + tmp);//填充上面申请到的主设备号到字符设备if(cdev_add(&chrdev[tmp],cur_id, 1) < 0){printk("Couldn't add chrdev!\r\n");return -EFAULT;}//根据创建的类生成一个设备节点device = device_create(class, NULL, cur_id, NULL, "led%d", tmp);}return 0; } //退出函数，此处为驱动模块的出口函数 static void __exit led_exit(void) {unsigned int tmp;dev_t cur_id;//以下实现各个寄存器的解除映射 iounmap(IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO04);iounmap(IOMUXC_SW_PAD_CTL_PAD_GPIO1_IO04);iounmap(IOMUXC_SW_MUX_CTL_PAD_CSI_HSYNC);iounmap(IOMUXC_SW_PAD_CTL_PAD_CSI_HSYNC);iounmap(IOMUXC_SW_MUX_CTL_PAD_CSI_VSYNC);iounmap(IOMUXC_SW_PAD_CTL_PAD_CSI_VSYNC);iounmap(GPIO1_GDIR);iounmap(GPIO1_DR);iounmap(GPIO4_GDIR);iounmap(GPIO4_DR);iounmap(CCM_CCGR1);iounmap(CCM_CCGR3);//以下销毁三个字符型设备及三个设备节点for (tmp=0; tmp < 3; tmp++) {//删除字符设备cdev_del(&chrdev[tmp]);cur_id = MKDEV(MAJOR(devid), MINOR(devid) + tmp);//销毁设备节点device_destroy(class, cur_id);}//释放主设备号unregister_chrdev_region(devid, 1);//销毁类class_destroy(class); } module_init(led_init); //模块入口声明 module_exit(led_exit); //模块出口声明 MODULE_LICENSE("GPL"); //GPL协议声明 MODULE_INFO(intree,"Y");
接下来是配套的Makefile文件，内容如下。
KERNEL_DIR=/opt/ebf_linux_kernel/build_image/build ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- export ARCH CROSS_COMPILE obj-m := led.o all:$(MAKE) -C $(KERNEL_DIR) M=$(CURDIR) modules modules clean:$(MAKE) -C $(KERNEL_DIR) M=$(CURDIR) clean
然后给出应用程序，内容如下，文件名为app.c。
#include <stdio.h> #include <fcntl.h> #include <string.h> #include <unistd.h> int main(int argc, char *argv[]) {int fd;unsigned char val = 0;if( argc != 3 ) //命令参数不对时提示 {printf("Usage :\n");printf("%s <all|red|green|blue> <on|off>\n", argv[0]);return 0;}if(strcmp(argv[1], "all") == 0){if(strcmp(argv[2], "on") == 0){val = 0; //值为0时点亮fd = open("/dev/led0", O_RDWR);//打开设备节点0write(fd, &val, 1); //把值写入设备节点0close(fd); //关闭设备节点0fd = open("/dev/led1", O_RDWR);//打开设备节点1write(fd, &val, 1); //把值写入设备节点1close(fd); //关闭设备节点1fd = open("/dev/led2", O_RDWR);//打开设备节点2write(fd, &val, 1); //把值写入设备节点2close(fd); //关闭设备节点2 }else{val = 1; //值为1时熄灭fd = open("/dev/led0", O_RDWR);//打开设备节点0write(fd, &val, 1); //把值写入设备节点0close(fd); //关闭设备节点0fd = open("/dev/led1", O_RDWR);//打开设备节点1write(fd, &val, 1); //把值写入设备节点1close(fd); //关闭设备节点1fd = open("/dev/led2", O_RDWR);//打开设备节点2write(fd, &val, 1); //把值写入设备节点2close(fd); //关闭设备节点2 }}else{if(strcmp(argv[1], "red") == 0){fd = open("/dev/led0", O_RDWR); //打开设备节点0if( fd < 0 )printf("can`t open\n");if(strcmp(argv[2], "on") == 0)val = 0; //值为0时红色点亮elseval = 1; //值为1时红色熄灭 }else if(strcmp(argv[1], "green") == 0){fd = open("/dev/led1", O_RDWR); //打开设备节点1if( fd < 0 )printf("can`t open\n");if(strcmp(argv[2], "on") == 0)val = 0; //值为0时绿色点亮elseval = 1; //值为1时绿色熄灭 }else if(strcmp(argv[1], "blue") == 0){fd = open("/dev/led2", O_RDWR); //打开设备节点2if( fd < 0 )printf("can`t open\n");if(strcmp(argv[2], "on") == 0)val = 0; //值为0时蓝色点亮elseval = 1; //值为1时蓝色熄灭 }write(fd, &val, 1); //把值写入设备节点close(fd); //关闭设备节点 }return 0; }
完成后，先执行make命令编译驱动程序，生成名为led.ko的驱动模块文件。然后对应用程序进行交叉编译，执行“arm-linux-gnueabihf-gcc app.c -o app”即可。最后，把编译生成的驱动模块文件led.ko和应用程序文件app一起拷贝到NFS共享目录下 ，并在开发板上执行“insmod led.ko”，把模块插入到内核中（可执行lsmod命令查看一下是否加载成功），之后可查看一下/dev目录，应该生成了三个设备节点文件led0、led1、led2，分别对应红、绿、蓝三个LED。此外，还可以执行“cat /proc/devices”查看一下led设备的主设备号。
以上都正常后，就可以执行应用程序来进行测试了。以控制红色为例，输入“./app red on”并回车，就可看到红色LED亮，输入“./app red off”并回车，就可看到红色LED灭，其他颜色的LED可如法进行测试。输入“./app all on”回车可实现三个LED全部点亮，输入“./app all off”回车实现三个LED全部熄灭。实验结果与“嵌入式Linux中的LED驱动控制”一文中的完全一样。
把上面的驱动代码和“嵌入式Linux中的LED驱动控制”一文中的代码进行比较可以看出，最大区别在于字符型cdev结构体一共注册了3个，设备节点也创建了3个。主设备号使用动态方式申请了1个，次设备号则指定了3个（0~2），即三个设备共用了一个驱动。
上面的代码中，最关键的是如何获取到打开文件的次设备号。本例在write接口函数中使用了函数iminor(file_inode(filp))来实现，minor函数调用了file_inode函数，file_inode的参数为file结构体指针。关于这部分的详细介绍可参考“嵌入式Linux中字符型驱动程序的基本框架”一文。其实，获取打开设备节点文件次设备的方式还有很多，比如使用函数iminor(inode)方式，或使用宏MINOR(inode->i_rdev)方式等等，返回值就是获取到的次设备号。