開發(fā)環(huán)境：

主機(jī)：Ubuntu12.04

開發(fā)板：RT5350

Openwrt：Openwrt15.05

1 硬件原理

下圖是我們溫度傳感器的接入引腳，3.3V 供電，io 口接 P13 的 GP0( GPIO0 的簡(jiǎn)稱 )。DHT11數(shù)字溫濕度傳感器 是一款含有已校準(zhǔn)數(shù)字信號(hào)輸出的溫濕度復(fù)合傳感器，它應(yīng)用專用的數(shù)字模塊采集技術(shù)和溫濕度傳感技術(shù)，確保產(chǎn)品具有極高的可靠性和卓越的長(zhǎng)期穩(wěn)定性。傳感器包括一個(gè)電阻式感濕元件和一個(gè)NTC測(cè)溫元件，并與一個(gè)高性能 8 位單片機(jī)相連接。因此該產(chǎn)品具有品質(zhì)卓越、超快響應(yīng)、抗干擾能力強(qiáng)、性價(jià)比極高等優(yōu)點(diǎn)。每個(gè)DHT11 傳感器都在極為精確的濕度校驗(yàn)室中進(jìn)行校準(zhǔn)。校準(zhǔn)系數(shù)以程序的形式存在OTP內(nèi)存中，傳感器內(nèi)部在檢測(cè)型號(hào)的處理過(guò)程中要調(diào)用這些校準(zhǔn)系數(shù)。單線制串行接口，使系統(tǒng)集成變得簡(jiǎn)易快捷。超小的體積、極低的功耗，使其成為該類應(yīng)用中，在苛刻應(yīng)用場(chǎng)合的最佳選擇。

2 DHT11 相關(guān)時(shí)序

• 初始化(復(fù)位)時(shí)序圖

1. 控制器首先至少拉低 18ms，然后拉高 20-40us 后等待 DHT11 的應(yīng)答
2. 當(dāng) DHT11 檢測(cè)到信號(hào)后，首先將總線拉低約 80us 然后在拉高 80us 作為應(yīng)答信號(hào)。

• 讀取數(shù)據(jù)時(shí)序圖

• 表示 0 的時(shí)序如下

• 表示 1 的時(shí)序如下

1. DHT11 以低電平應(yīng)答主機(jī)，然后拉高總線準(zhǔn)備輸出。輸出 0 信號(hào)和 1 信號(hào)都是以低電平開始高電平結(jié)束。
2. DHT11 輸出 0、 1 信號(hào)的低電平時(shí)間相同，而高電平的時(shí)間不同，輸出 0 信號(hào)時(shí)高電平約 26-28us,而當(dāng)輸出 1 信號(hào)時(shí)高電平約為 70us。

3 驅(qū)動(dòng)程序

關(guān)于字符設(shè)備驅(qū)動(dòng)程序的使用，我們可以參照點(diǎn)亮 led 燈的那個(gè)實(shí)驗(yàn)，這里只給出跟DHT11 密切相關(guān)的驅(qū)動(dòng)程序，詳細(xì)的程序請(qǐng)查看我們的驅(qū)動(dòng)文件！

//配置連接溫度傳感器的引腳
#define DHT11_L	   	        *GPIO21_0_DATA &= ~(1< //低電平	
#define DHT11_H		        *GPIO21_0_DATA |=  (1< //高電平
#define DHT11_OUT	        *GPIO21_0_DIR  |=  (1< //輸出	
#define DHT11_IN		*GPIO21_0_DIR  &= ~(1< //輸入	
#define DHT11_STA		*GPIO21_0_DATA & 0x01	

//寄存器定義
volatile unsigned long *GPIO21_0_DIR;
volatile unsigned long *GPIO21_0_DATA;	


/****************  基本定義 **********************/
//初始化函數(shù)必要資源定義
//用于初始化函數(shù)當(dāng)中
//device number;
	dev_t dev_num;
//struct dev
	struct cdev dht11_cdev;
//auto "mknode /dev/dht11 c dev_num minor_num"
struct class *dht11_class = NULL;
struct device *dht11_device = NULL;

/********************  dht11有關(guān)的函數(shù)   ****************************/
//從dht11中讀取一個(gè)字節(jié)
static unsigned char read_byte(void)
{
	unsigned char r_val = 0; 
	unsigned char t_count = 0; //計(jì)時(shí)器，防止超時(shí)；
        unsigned char i;

	for(i = 0 ; i < 8 ; i++)
	{
		t_count = 0;
		
		while(!DHT11_STA)
		{
			udelay(1);
			t_count++;
			if(t_count >250)
			{
				printk("read_byte error1n");
				return 100;
			}
		}
		t_count = 0;

		udelay(32);

		if(DHT11_STA == 1)
		{
			r_val < <= 1;
			r_val |= 1;
		}
		else
		{
			r_val < <= 1;
			continue;
		}

		while( DHT11_STA == 1 )
		{
			udelay(2);
			t_count++;
			if(t_count >250)
			{
				printk("read_byte error2n");
				return 100;
			}
	 	 }
	}

	return r_val;
}

//從dht11中讀出數(shù)據(jù)
static unsigned int read_dht11(void)
{
	 unsigned char t_count = 0; //計(jì)時(shí)器；
	 unsigned int  dht11 = 0;
	 unsigned char h_i = 0 , h_f = 0;
	 unsigned char t_i = 0 , t_f = 0;
	 unsigned char check_sum = 0;

	 DHT11_OUT;

	 DHT11_L;
	 mdelay(30); // >18ms;
	 DHT11_H;

	 udelay(30);

	 DHT11_IN;
	 while(DHT11_STA == 1)
	 {
	 	udelay(1);
		t_count++;

		if(t_count > 50)
		{
	 		printk("device error: dht11!n");
			return 0;
		}
	 }
	 t_count = 0;

 	 while(!DHT11_STA)
	 {
		udelay(1);
		t_count++;

		if(t_count > 250)
		{
			printk("read_dht11 error1n");
			return 0;
		}
	 }

	 t_count = 0;

	 udelay(50);

	 while(DHT11_STA)
	 {
		udelay(1);
		t_count++;
		if(t_count > 250)
		{
			printk("read_dht11 error2n");
			return 0;
		}
	 }

	 h_i = read_byte();
	 h_f = read_byte();
	 t_i = read_byte();
	 t_f = read_byte();
	 check_sum = read_byte();

	 if(check_sum == (h_i+h_f+t_i+t_f) || (h_i!=100 && t_i != 100))
	 {
		dht11 = t_i;
		dht11 < <= 8;
		dht11 += h_i;
	 }
	 else
	 {
		dht11 = 0;
		printk("read_dht11 error3n");
	 }

	 return dht11;
}


/**********************************************************************/

/**************** 結(jié)構(gòu)體 file_operations 成員函數(shù) *****************/
//open
static int dht11_open(struct inode *inode, struct file *file)
{
	printk("dht11 drive open...n");

	DHT11_OUT;
	DHT11_H;

	return 0;
}

//close
static int dht11_close(struct inode *inode , struct file *file)
{
	return 0;
}

//read
static ssize_t dht11_read(struct file *file, char __user *buffer,
			size_t len, loff_t *pos)
{
	unsigned int dht11; 
	printk("dht11 drive read...n");

	dht11 = read_dht11();
	copy_to_user(buffer, &dht11, 4);

	return 4;
}



/***************** 結(jié)構(gòu)體： file_operations ************************/
//struct
static const struct file_operations dht11_fops = {
	.owner   = THIS_MODULE,
	.open	 = dht11_open,
	.release = dht11_close,	
	.read	 = dht11_read,
};


/*************  functions: init , exit*******************/
//條件值變量，用于指示資源是否正常使用
unsigned char init_flag = 0;
unsigned char add_code_flag = 0;

//init
static __init int dht11_init(void)
{
	int ret_v = 0;
	printk("dht11 drive init...n");

	//函數(shù)alloc_chrdev_region主要參數(shù)說(shuō)明：
	//參數(shù)2： 次設(shè)備號(hào)
	//參數(shù)3： 創(chuàng)建多少個(gè)設(shè)備
	if( ( ret_v = alloc_chrdev_region(&dev_num,0,1,"dht11") ) < 0 )
	{
		goto dev_reg_error;
	}
	init_flag = 1; //標(biāo)示設(shè)備創(chuàng)建成功；

	printk("The drive info of dht11:nmajor: %dnminor: %dn",
		MAJOR(dev_num),MINOR(dev_num));

	cdev_init(&dht11_cdev,&dht11_fops);
	if( (ret_v = cdev_add(&dht11_cdev,dev_num,1)) != 0 )
	{
		goto cdev_add_error;
	}

	dht11_class = class_create(THIS_MODULE,"dht11");
	if( IS_ERR(dht11_class) )
	{
		goto class_c_error;
	}

	dht11_device = device_create(dht11_class,NULL,dev_num,NULL,"dht11");
	if( IS_ERR(dht11_device) )
	{
		goto device_c_error;
	}
	printk("auto mknod success!n");

	//------------   請(qǐng)?jiān)诖颂砑幽某跏蓟绦? --------------//
       

	GPIO21_0_DATA = (volatile unsigned long *)ioremap(0x10000620, 4);
	GPIO21_0_DIR =  (volatile unsigned long *)ioremap(0x10000624, 4);

        //如果需要做錯(cuò)誤處理，請(qǐng)：goto dht11_error;	

	 add_code_flag = 1;
	//----------------------  END  ---------------------------// 

	goto init_success;

dev_reg_error:
	printk("alloc_chrdev_region failedn");	
	return ret_v;

cdev_add_error:
	printk("cdev_add failedn");
 	unregister_chrdev_region(dev_num, 1);
	init_flag = 0;
	return ret_v;

class_c_error:
	printk("class_create failedn");
	cdev_del(&dht11_cdev);
 	unregister_chrdev_region(dev_num, 1);
	init_flag = 0;
	return PTR_ERR(dht11_class);

device_c_error:
	printk("device_create failedn");
	cdev_del(&dht11_cdev);
 	unregister_chrdev_region(dev_num, 1);
	class_destroy(dht11_class);
	init_flag = 0;
	return PTR_ERR(dht11_device);

//------------------ 請(qǐng)?jiān)诖颂砑幽腻e(cuò)誤處理內(nèi)容 ----------------//
dht11_error:
	add_code_flag = 0;
	return -1;
//--------------------          END         -------------------//
    
init_success:
	printk("dht11 init success!n");
	return 0;
}

//exit
static __exit void dht11_exit(void)
{
	printk("dht11 drive exit...n");	

	if(add_code_flag == 1)
 	{   
           //----------   請(qǐng)?jiān)谶@里釋放您的程序占有的資源   ---------//
	    printk("free your resources...n");	               

		iounmap(GPIO21_0_DATA);
		iounmap(GPIO21_0_DIR);

	    printk("free finishn");		               
	    //----------------------     END      -------------------//
	}					            

	if(init_flag == 1)
	{
		//釋放初始化使用到的資源;
		cdev_del(&dht11_cdev);
 		unregister_chrdev_region(dev_num, 1);
		device_unregister(dht11_device);
		class_destroy(dht11_class);
	}
}

/**************** module operations**********************/
//module loading
module_init(dht11_init);
module_exit(dht11_exit);

//some infomation
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR("from Jafy");
MODULE_DESCRIPTION("dht11 drive");
/*********************  The End ***************************/

4 應(yīng)用程序

int main(int argc, char **argv)
{
	int fd;
	unsigned int dht11 = 0;
	unsigned int humi,temp;

	//打開溫度傳感器驅(qū)動(dòng)模塊
	fd = open("/dev/dht11", O_RDWR | O_NONBLOCK);
	if (fd < 0)
	{
		printf("can't open /dev/dht11n");
		return -1;
	}

	read(fd, &dht11, sizeof(dht11));

	temp = dht11 >>8;
	humi = dht11 &0x000000ff;
	printf("the current temperature is: %dn",temp);
	printf("the current humidity is:    %dn",humi);

	close(fd);
	
	return 0;
}

5 實(shí)驗(yàn)結(jié)果

審核編輯：湯梓紅