S5PV210（TQ210）学习笔记——按键驱动程序

经过前面的配置，S5PV210开发已经可以成功进入Linux控制台了，那么，有了这个环境就可以开始学习Linux驱动的编写和测试了。学习Linux设备驱动，通常是从字符设备驱动开始。我写的第一个驱动程序是Led的，其实也就是熟悉下字符设备驱动的基本结构，本文以中断方式的按键驱动为例，简单的介绍下字符设备驱动程序。

一按键驱动程序的简单实现

下面是基于中断和消息的按键驱动程序，其工作原理是：当应用程序读取键值时，会调用按键驱动程序的read函数，而我们实现的read函数检测完读取长度后没有直接读取键值而是等待按键消息，如果没有按键，程序会进入休眠状态，这样可以节省大量的CPU，而当我们按键时硬件会产生中断，程序自动进入中断处理函数，在中断处理函数中，驱动程序读取键值存入全局变量并激活read函数中等待的消息，应用程序被迅速唤醒并通过read函数读取键值，如此，完成了获取键值的工作。下面是源码，比较简单，也就不多说了。

源码：

[cpp]
#include <linux/types.h>
#include <linux/module.h>
#include <linux/cdev.h>
#include <linux/fs.h>
#include <linux/device.h>
#include <linux/gpio.h>
#include <linux/irq.h>
#include <linux/interrupt.h>
#include <linux/sched.h>
#include <linux/wait.h>
#include <linux/uaccess.h>

static dev_t devno;
static struct cdev cdev;
static struct class* buttons_class;
static struct device* buttons_device;

static wait_queue_head_t button_waitq;

static volatile int pressed = 0;
static unsigned char key_val;

struct key_desc{
    unsigned int pin;
    unsigned char value;
};

static struct key_desc key_descs[8] = {
    [0] = {
        .pin = S5PV210_GPH0(0),
        .value = 0x00,
    },

    [1] = {
        .pin = S5PV210_GPH0(1),
        .value = 0x01,
    },

    [2] = {
        .pin = S5PV210_GPH0(2),
        .value = 0x02,
    },

    [3] = {
        .pin = S5PV210_GPH0(3),
        .value = 0x03,
    },

    [4] = {
        .pin = S5PV210_GPH0(4),
        .value = 0x04,
    },

    [5] = {
        .pin = S5PV210_GPH0(5),
        .value = 0x05,
    },

    [6] = {
        .pin = S5PV210_GPH2(6),
        .value = 0x06,
    },

    [7] = {
        .pin = S5PV210_GPH2(7),
        .value = 0x07,
    },
};

static irqreturn_t buttons_irq(int irq, void *dev_id){
    volatile struct key_desc *key = (volatile struct key_desc *)dev_id;

    if(gpio_get_value(key->pin)){
        key_val = key->value|0x80;
    }
    else{
        key_val = key->value;
    }

    pressed = 1;
    wake_up_interruptible(&button_waitq);

    return IRQ_RETVAL(IRQ_HANDLED);
}

static int buttons_open(struct inode *inode, struct file *file){
    int ret;

    ret = request_irq(IRQ_EINT(0),   buttons_irq, IRQ_TYPE_EDGE_BOTH, "key1", &key_descs[0]);
    if(ret)
        return ret;
    ret = request_irq(IRQ_EINT(1),   buttons_irq, IRQ_TYPE_EDGE_BOTH, "key2", &key_descs[1]);
    if(ret)
        return ret;
    ret = request_irq(IRQ_EINT(2),   buttons_irq, IRQ_TYPE_EDGE_BOTH, "key3", &key_descs[2]);
    if(ret)
        return ret;
    ret = request_irq(IRQ_EINT(3),   buttons_irq, IRQ_TYPE_EDGE_BOTH, "key4", &key_descs[3]);
    if(ret)
        return ret;
    ret = request_irq(IRQ_EINT(4),   buttons_irq, IRQ_TYPE_EDGE_BOTH, "key5", &key_descs[4]);
    if(ret)
        return ret;
    ret = request_irq(IRQ_EINT(5),   buttons_irq, IRQ_TYPE_EDGE_BOTH, "key6", &key_descs[5]);
    if(ret)
        return ret;
    ret = request_irq(IRQ_EINT(22), buttons_irq, IRQ_TYPE_EDGE_BOTH, "key7", &key_descs[6]);
    if(ret)
        return ret;
    ret = request_irq(IRQ_EINT(23), buttons_irq, IRQ_TYPE_EDGE_BOTH, "key8", &key_descs[7]);
    if(ret)
        return ret;
    return 0;
}

static ssize_t buttons_read(struct file * file, char __user *data, size_t count, loff_t *loff){
    if(count != 1){
        printk(KERN_ERR "The driver can only give one key value once!\n");
        return -ENOMEM;
    }

    wait_event_interruptible(button_waitq, pressed);
    pressed = 0;

    if(copy_to_user(data, &key_val, 1)){
        printk(KERN_ERR "The driver can not copy the data to user area!\n");
        return -ENOMEM;
    }

    return 0;
}

static int buttons_close(struct inode *inode, struct file *file){
    free_irq(IRQ_EINT(0), &key_descs[0]);
    free_irq(IRQ_EINT(1), &key_descs[1]);
&

补充：软件开发 , C++ ,