驱动-----dht11温湿度传感器

单总线：只用一根线。

复位信号：设置为输出模式，低电平20ms，然后再拉高30us。然后设置为输入模式，dht11会先拉低80us，然后拉高80us表示对接成功

数据0：开始先拉低50us，然后拉高26~28us表示0

数据1：开始拉低50us,然后拉高70us表示1

每传输一位的数据都要间隔一个拉低50us

梳理一下时序：

应用程序：

#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/module.h>
#include <asm/io.h>
#include <asm/string.h>
#include <asm/uaccess.h>
#include <linux/miscdevice.h>
#include <asm-generic/errno-base.h>
#include <mach/gpio-nrs.h>
#include <mach/gpio.h>
#include <linux/delay.h>

#define DEV_NAME "dht11"
#define PIN_DHT11 S3C2410_GPF(6)

static void dht11_start(void)
{
	gpio_request(PIN_DHT11, "pin_dht11");
	gpio_direction_output(PIN_DHT11, 1);
	msleep(40);
	gpio_set_value(PIN_DHT11, 0);
	mdelay(18);
	gpio_set_value(PIN_DHT11, 1);
	udelay(30);
	gpio_direction_input(PIN_DHT11);
}

static int dht11_wait_respon(void)
{
	int time = 100;
	while((time > 0) && gpio_get_value(PIN_DHT11))
	{
		udelay(1);
		time--;
	}

	if(time <= 0)
	{
		printk("dht11_wait_respon   1\n");
		return -1;
	}

	time = 100;
	while((time > 0) && (!gpio_get_value(PIN_DHT11)))
	{
		udelay(1);
		time--;
	}

	if(time <= 0)
	{
		printk("dht11_wait_respon   2\n");
		return -1;
	}

	time = 100;
	while((time > 0) && gpio_get_value(PIN_DHT11))
	{
		udelay(1);
		time--;
	}

	if(time <= 0)
	{
		printk("dht11_wait_respon   3\n");
		return -1;
	}

	return 0;
}

static int get_bit(void)
{
	int time = 100;
	while((time > 0) && (!gpio_get_value(PIN_DHT11)))
	{
		udelay(1);
		time--;
	}

	if(time <= 0)
	{
		printk("get_bit   1\n");
		return -1;
	}

	udelay(30);

	if(0 == gpio_get_value(PIN_DHT11))
		return 0;
	
	time = 100;
	while((time > 0) && gpio_get_value(PIN_DHT11))
	{
		udelay(1);
		time--;
	}

	if(time <= 0)
	{
		printk("get_bit   2\n");
		return -1;
	}

	return 1;
}

static int dht11_get_data(unsigned char * data)
{
	int i = 0;
	int j = 0;
	for(j = 0; j < 5; j++)
	{
		for(i = 0; i < 8; i++)
		{
			char tmp = 0;
			data[j] <<= 1;
			tmp = get_bit();	
			if(tmp < 0)
				return -1;
			data[j] |= tmp;
		}
	}

	return 0;
}

static int open (struct inode * inode, struct file * file)
{
	printk("dht11 open ...\n");
	return 0;
}

static ssize_t read (struct file * file, char __user * buf, size_t len, loff_t * offset)
{
	int ret = 0;
	unsigned char data[5] = {0};
	dht11_start();
	ret = dht11_wait_respon();
	if(ret < 0)
		return -1;

	ret = dht11_get_data(data);
	if(ret < 0)
		return -1;
	copy_to_user(buf, data, sizeof(data));
	printk("dht11 read ...\n");
	return 0;
}

static ssize_t write (struct file * file, const char __user * buf, size_t len, loff_t * offset)
{
	return 0;
}

static int close (struct inode * inode, struct file * file)
{
	printk("dht11 close ...\n");
	return 0;
}

static struct file_operations fops = 
{
	.owner = THIS_MODULE,
	.open = open,
	.read = read,
	.write = write,
	.release = close
};

static struct miscdevice misc = 
{
	.minor = MISC_DYNAMIC_MINOR,
	.name = DEV_NAME,
	.fops = &fops
};

static int __init dht11_init(void)
{
	int ret = misc_register(&misc);
	if(ret < 0)
		goto err_misc_register;

	printk("dht11_init  ...\n");
	return ret;

err_misc_register:
	misc_deregister(&misc);
	printk("dht11 misc_register faidht11\n");	
	return ret;
}

static void __exit dht11_exit(void)
{
	misc_deregister(&misc);
	printk("dht11_exit  ###############################\n");
}

module_init(dht11_init);
module_exit(dht11_exit);
MODULE_LICENSE("GPL");