1 硬件原理

下图是我们温度传感器的接入引脚，3.3V 供电，io 口接 P13 的 GP0( GPIO0 的简称 )。DHT11数字温湿度传感器是一款含有已校准数字信号输出的温湿度复合传感器，应用专用的数字模块采集技术和温湿度传感技术，确保产品具有极高的可靠性和很好的长期稳定性。传感器包括一个电阻式感湿元件和一个NTC测温元件，并与一个高性能 8 位单片机相连接。因此该产品具有品质很好、超快响应、抗干扰能力强、性价比极高等优点。每个DHT11 传感器都在极为精确的湿度校验室中进行校准。校准系数以程序的形式存在OTP内存中，传感器内部在检测型号的处理过程中要调用这些校准系数。单线制串行接口，使系统集成变得简易快捷。超小的体积、极低的功耗，使其成为该类应用中，在苛刻应用场合的最佳选择。

2 DHT11 相关时序

初始化(复位)时序图

控制器首先至少拉低 18ms，然后拉高 20-40us 后等待 DHT11 的应答
当 DHT11 检测到信号后，首先将总线拉低约 80us 然后在拉高 80us 作为应答信号。

读取数据时序图

表示 0 的时序如下

表示 1 的时序如下

DHT11 以低电平应答主机，然后拉高总线准备输出。输出 0 信号和 1 信号都是以低电平开始高电平结束。
DHT11 输出 0、 1 信号的低电平时间相同，而高电平的时间不同，输出 0 信号时高电平约 26-28us,而当输出 1 信号时高电平约为 70us。

3 驱动程序

关于字符设备驱动程序的使用，我们可以参照点亮 led 灯的那个实验，这里只给出跟DHT11 密切相关的驱动程序，详细的程序请查看我们的驱动文件！

//配置连接温度传感器的引脚#define DHT11_L *GPIO21_0_DATA &= ~(1< < 0) //低电平#define DHT11_H *GPIO21_0_DATA |= (1< < 0) //高电平#define DHT11_OUT *GPIO21_0_DIR |= (1< < 0) //输出#define DHT11_IN*GPIO21_0_DIR &= ~(1< < 0) //输入#define DHT11_STA*GPIO21_0_DATA & 0x01//寄存器定义volatile unsigned long *GPIO21_0_DIR;volatile unsigned long *GPIO21_0_DATA;//初始化函数必要资源定义//用于初始化函数当中//devICe number;dev_t dev_num;//struct devstruct cdev dht11_cdev;//auto "mknode /dev/dht11 c dev_num minor_num"struct class *dht11_class = NULL;struct devICe *dht11_device = NULL;//从dht11中读取一个字节static unsigned char read_byte(void){unsigned char r_val = 0; unsigned char t_count = 0; //计时器，防止超时； 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;}//从dht11中读出数据static unsigned int read_dht11(void){ unsigned char t_count = 0; //计时器； 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;}//openstatic int dht11_open(struct inode *inode, struct file *file){printk("dht11 drive open...n");DHT11_OUT;DHT11_H;return 0;}//closestatic int dht11_close(struct inode *inode , struct file *file){return 0;}//readstatic 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;}//structstatic const struct file_operations dht11_fops = {.owner = THIS_Module,.open = dht11_open,.release = dht11_close,.read = dht11_read,};//条件值变量，用于指示资源是否正常使用unsigned char init_flag = 0;unsigned char add_code_flag = 0;//initstatic __init int dht11_init(void){int ret_v = 0;printk("dht11 drive init...n");//函数alloc_chrdev_region主要参数说明：//参数2： 次设备号//参数3： 创建多少个设备if( ( ret_v = alloc_chrdev_region(&dev_num,0,1,"dht11") ) < 0 ){goto dev_reg_error;}init_flag = 1; //标示设备创建成功；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");//------------ 请在此添加您的初始化程序 --------------// GPIO21_0_DATA = (volatile unsigned long *)ioremap(0x10000620, 4);GPIO21_0_DIR = (volatile unsigned long *)ioremap(0x10000624, 4); //如果需要做错误处理，请：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);//------------------ 请在此添加您的错误处理内容 ----------------//dht11_error:add_code_flag = 0;return -1;//-------------------- END -------------------// init_success:printk("dht11 init success!n");return 0;}//exitstatic __exit void dht11_exit(void){printk("dht11 drive exit...n");if(add_code_flag == 1) { //---------- 请在这里释放您的程序占有的资源 ---------// printk("free your resources...n"); iounmap(GPIO21_0_DATA);iounmap(GPIO21_0_DIR); printk("free finishn"); //---------------------- END -------------------//} if(init_flag == 1){//释放初始化使用到的资源;cdev_del(&dht11_cdev); unregister_chrdev_region(dev_num, 1);device_unregister(dht11_device);class_destroy(dht11_class);}}//module loadingmodule_init(dht11_init);module_exit(dht11_exit);//some infomationMODULE_LICENSE("GPL v2");MODULE_AUTHOR("fROM Jafy");MODULE_DESCRIPTION("dht11 drive");

4 应用程序

int main(int argc, char **argv){int fd;unsigned int dht11 = 0;unsigned int humi,temp;//打开温度传感器驱动模块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;}