嵌入式Linux中的LED驱动控制
在前面“嵌入式Linux中字符型驱动程序的基本框架”一文中，讨论了一个字符型驱动的基本框架，但没有实现具体的驱动任务。这里就以野火i.MX6ULL开发板为例，通过编写一个实际的驱动程序去控制开发板上三个LED的亮灭。
先来看一下LED部分的电路原理图，如下所示。
从上图中可以看到，三个RGB的二极管采用共阳接法， 因此在给i.MAX6ULL的GPIO_4、CSI_HSYNC、CSI_VSYNC端口输出高电平时，三个发光管匀熄灭，输出低电平时，三个发光管匀点亮。
下面给出了完整的驱动程序代码，文件名为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; //声明一个字符型设备结构体led_dev struct led_dev { dev_t devid; //设备号 struct cdev chrdev; //字符设备结构体 struct class *class; //类结构体 struct device *device; //设备结构体 }; //定义一个led_dev类型的结构体，名称为led struct led_dev led; //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); filp->private_data = &led; //把led结构体保存在file结构体的私有变量中 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 long ret; unsigned char value = 7; unsigned int tmp; ret = copy_from_user(&value, buf, cnt); //从应用空间获取值 if(ret < 0) { printk("kernel write failed!\r\n"); return -EFAULT; } switch(value) //根据应用空间的值判断具体操作 { case 0: //全部点亮三个LED tmp = ioread32(GPIO1_DR); tmp &= ~(1<<4); iowrite32(tmp, GPIO1_DR); tmp = ioread32(GPIO4_DR); tmp &= ~(1<<20 | 1<<19); iowrite32(tmp, GPIO4_DR); break; case 1: //点亮红色LED tmp = ioread32(GPIO1_DR); tmp &= ~(1<<4); iowrite32(tmp, GPIO1_DR); break; case 2: //点亮绿色LED tmp = ioread32(GPIO4_DR); tmp &= ~(1<<20); iowrite32(tmp, GPIO4_DR); break; case 3: //点亮蓝色LED tmp = ioread32(GPIO4_DR); tmp &= ~(1<<19); iowrite32(tmp, GPIO4_DR); break; case 4: //熄灭红色LED tmp = ioread32(GPIO1_DR); tmp |= (1<<4); iowrite32(tmp, GPIO1_DR); break; case 5: //熄灭绿色LED tmp = ioread32(GPIO4_DR); tmp |= (1<<20); iowrite32(tmp, GPIO4_DR); break; case 6: //熄灭蓝色LED tmp = ioread32(GPIO4_DR); tmp |= (1<<19); iowrite32(tmp, GPIO4_DR); break; case 7: //全部熄灭三个LED tmp = ioread32(GPIO1_DR); tmp |= (1<<4); iowrite32(tmp, GPIO1_DR); tmp = ioread32(GPIO4_DR); tmp |= (1<<20 | 1<<19); iowrite32(tmp, GPIO4_DR); break; default: break; } return 0; } //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, .write = led_write, .release = led_release, }; //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; //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(&led.devid, 0, 1, "led") < 0) { printk("Couldn't alloc_chrdev_region!\r\n"); return -1; } led.chrdev.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(&led.chrdev, &led_dev_fops); //填充上面申请到的主设备号到字符设备 if(cdev_add(&led.chrdev,led.devid, 1) < 0) { printk("Couldn't add chrdev!\r\n"); return -1; } //创建类 led.class = class_create(THIS_MODULE, "led_dev"); //根据创建的类生成一个设备节点 led.device = device_create(led.class, NULL, led.devid, NULL, "led"); return 0; } //退出函数，此处为驱动模块的出口函数 static void __exit led_exit(void) { //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); //删除字符设备 cdev_del(&led.chrdev); //释放主设备号 unregister_chrdev_region(led.devid, 1); //销毁设备节点 device_destroy(led.class, led.devid); //销毁类 class_destroy(led.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");
驱动程序属于内核态程序，所以还需要配套一个Makefile文件，其内容如下。
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 clean: $(MAKE) -C $(KERNEL_DIR) M=$(CURDIR) clean
上述Makefile文件中的第一行指定了开发板的内核源代码位置，若放到了其他路径可自行修改。另外，该内容在复制粘贴后，需要修改命令两行（倒数第1、3行）前面的空余部分，修改为Tab键开头。
以下是测试用的应用程序代码，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; fd = open("/dev/led", O_RDWR); //打开设备节点 if( fd < 0 ) printf("can`t open\n"); 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时全部点亮 else val = 7; //值为7时全部熄灭 } else if(strcmp(argv[1], "red") == 0) { if(strcmp(argv[2], "on") == 0) val = 1; //值为1时红色点亮 else val = 4; //值为4时红色熄灭 } else if(strcmp(argv[1], "green") == 0) { if(strcmp(argv[2], "on") == 0) val = 2; //值为2时绿色点亮 else val = 5; //值为5时绿色熄灭 } else if(strcmp(argv[1], "blue") == 0) { if(strcmp(argv[2], "on") == 0) val = 3; //值为3时蓝色点亮 else val = 6; //值为6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，若成功会生成名为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。
完成后，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 。然后在开发板上执行“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，并查看一下/dev目录是否已经生成了设备节点文件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。输入“./app all on”并回车，可看到开发板上三个LED全部点亮，如下图所示。
再输入“./app all off”并回车，可看到它们又全部熄灭，如下图所示。
还可以执行其他命令，来点亮或熄灭单独的LED，比如，单独点亮红色的LED，可执行命“./app red on”，熄灭执行命令“./app red off”等等，以此类推进行检查验证。
--待续--
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