嵌入式Linux LED驱动开发

一、LED驱动概述

本笔记基于IMX6ULL处理器的LED驱动开发，详细介绍了字符设备驱动开发的基本流程。该驱动实现了对LED的基本控制功能，通过字符设备接口供用户空间程序调用。

二、LED驱动核心概念

1. 寄存器地址定义

本驱动涉及多个硬件寄存器的配置：

#define CCM_CGR1_BASE        0x020C406C // 时钟控制寄存器
#define SW_MUX_GPIO1_IO03_BASE 0x020E0068 // 引脚复用配置
#define SW_PAD_GPIO1_IO03_BASE 0x020E02F4 // 引脚电气特性配置
#define GPIO1_DR_BASE        0x0209C000 // 数据寄存器
#define GPIO1_GDIR_BASE      0x0209C004 // 方向寄存器

2. 寄存器操作方法

ioremap：将物理地址映射到内核虚拟地址空间
readl：读取寄存器值
writel：写入寄存器值
iounmap：解除地址映射

3. LED状态定义

#define LEDOFF 0 // LED关闭
#define LEDON  1 // LED开启

三、LED驱动开发步骤

1. 驱动模块初始化与卸载

static int __init led_init(void) {// 初始化代码
}static void __exit led_exit(void) {// 清理代码
}module_init(led_init);
module_exit(led_exit);

2. 硬件初始化

地址映射

CCM_CGR1 = ioremap(CCM_CGR1_BASE, 4);
SW_MUX_GPIO1_IO03 = ioremap(SW_MUX_GPIO1_IO03_BASE, 4);
SW_PAD_GPIO1_IO03 = ioremap(SW_PAD_GPIO1_IO03_BASE, 4);
GPIO1_DR = ioremap(GPIO1_DR_BASE, 4);
GPIO1_GDIR = ioremap(GPIO1_GDIR_BASE, 4);

时钟使能

val = readl(CCM_CGR1);
val &= ~(3 << 26); // 清除旧设置
val |= (3 << 26);  // 启用GPIO1时钟
writel(val, CCM_CGR1);

引脚配置

writel(0x5, SW_MUX_GPIO1_IO03); // 设置为GPIO模式
writel(0x10B0, SW_PAD_GPIO1_IO03); // 配置电气特性

GPIO方向设置

val = readl(GPIO1_GDIR);
val |= (1 << 3); // 设置GPIO1_IO03为输出
writel(val, GPIO1_GDIR);

3. 设备操作函数实现

LED开关函数

static void led_switch(unsigned char state) {unsigned int val = 0;val = readl(GPIO1_DR);if (state == LEDON) {val &= ~(1 << 3); // 拉低电压点亮LED} else if (state == LEDOFF) {val |= (1 << 3); // 拉高电压关闭LED}writel(val, GPIO1_DR);
}

文件操作结构体

static const struct file_operations led_fops = {.owner = THIS_MODULE,.write = led_write,.open = led_open,.release = led_release,
};

open和release函数

static int led_open(struct inode *inode, struct file *file) {printk("LED device opened\n");return 0;
}static int led_release(struct inode *inode, struct file *file) {printk("LED device closed\n");return 0;
}

write函数

static ssize_t led_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos) {int ret = 0;unsigned char databuf[1];ret = copy_from_user(databuf, buf, count);if (ret < 0) {printk("Failed to copy data from user space\n");return -EIO;}led_switch(databuf[0]);return 0;
}

4. 模块注册与注销

static int __init led_init(void) {// ...ret = register_chrdev(LED_MAJOR, LED_NAME, &led_fops);// ...
}static void __exit led_exit(void) {// ...unregister_chrdev(LED_MAJOR, LED_NAME);// ...
}

四、用户空间测试程序

1. 测试程序功能

int main(int argc, char *argv[]) {if (argc != 3) {fprintf(stderr, "Usage: %s <led_device> <0|1>\n", argv[0]);return -1;}char* filename;unsigned char databuf[1];filename = argv[1];databuf[0] = atoi(argv[2]);int fd = 0;int ret = 0;fd = open(filename, O_RDWR);if (fd < 0) {perror("open led device error");return -1;}ret = write(fd, databuf, 1);if (ret < 0) {perror("write led device error");close(fd);return -1;}close(fd);return 0;
}

2. 测试方法

# 编译测试程序
arm-linux-gnueabihf-gcc ledAPP.c -o ledAPP# 加载驱动
sudo insmod led.ko# 创建设备节点
sudo mknod /dev/led c 200 0# 点亮LED
sudo ./ledAPP /dev/led 1# 关闭LED
sudo ./ledAPP /dev/led 0

五、Makefile说明

KERNERDIR := /home/ubuntu2004/linux/IMX6ULL/linux/linux-imx-rel_imx_4.1.15_2.1.0_ga
CURRENTDIR := $(shell pwd)obj-m := led.obuild : kernel_moduleskernel_modules:$(MAKE) -C $(KERNERDIR) M=$(CURRENTDIR) modulesclean:$(MAKE) -C $(KERNERDIR) M=$(CURRENTDIR) clean