DHT11
dht11和ds18b20很类似，都是使用单总线通信的。
3种编程实现方式：
- 查询方式，直接操作gpio，时序通过延时等待实现等
- 中断方式，通过设置双边沿触发中断，获取时序中高低电平时间，根据时间来判定解析时序
对于dht11的工作原理，参考别人文章即可：https://blog.csdn.net/qq_44981039/article/details/110185982
驱动实现
野火imx6ull开发板原理图
设备树编写
根节点下添加：dht11
dht11 {
compatible = "xgj,dht11";
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_ds18b20>;
dht11-gpios = <&gpio1 2 GPIO_ACTIVE_HIGH>;
status = "okay";
}
iomuxc节点下添加：
/*ds18b20*/
pinctrl_ds18b20: ds18b20grp {
fsl,pins = <
MX6UL_PAD_GPIO1_IO02__GPIO1_IO02 0x10b0
>;
};
设备树编译：
ares@ubuntu:~/work/ebf_linux_kernel-ebf_4.19.35_imx6ul$ cat make_dtb.sh
#!/bin/sh
make ARCH=arm -j4 CROSS_COMPILE=arm-linux-gnueabihf- dtbs
将设备树拷贝系统目录：
debian@npi:~/nfs_root/driver$ cat cp_dtb_to_linux.sh
#!/bin/sh
sudo cp imx6ull-mmc-npi.dtb /usr/lib/linux-image-4.19.35-carp-imx6/
- /usr/lib/linux-image-4.19.35-carp-imx6/ ，系统存放设备树的目录
重启系统设备树生效：
sudo reboot
驱动编写
typedefunsignedcharuint8_t;
#define DEV_DTS_NODE_PATH "/dht11"/* 设备树节点的路径，在根节点下 */
#define DEV_PIN_DTS_NAME "dht11-gpios"/* GPIO引脚的属性名 */
#define DEV_NAME "dht11"/* 设备名 /dev/dht11 */
#define DEV_DTS_COMPATIBLE "xgj,dht11"/* 设备匹配属性 compatible */
#define DHT11_PIN dht11_dev.gpio
#define DHT11_IO_OUT() gpio_direction_output(DHT11_PIN, 1);
#define DHT11_IO_IN() gpio_direction_input(DHT11_PIN)
#define DHT11_WRITE(bit) gpio_set_value(DHT11_PIN, bit)
#define DHT11_READ() gpio_get_value(DHT11_PIN)
structdht11 {
int gpio; /* gpio */
int irq;
dev_t dev_no; /* 设备号 */
structcdevchrdev;
structclass *class;
spinlock_t lock;
};
staticintdht11_wait_for_ready(void)
{
int timeout;
timeout = 400;
while (DHT11_READ() && timeout) /* 等待低电平到来 */
{
udelay(1);
--timeout;
}
if (!timeout)
{
printk("timeout %d\n", __LINE__);
return-1; /* 超时 */
}
timeout = 1000;
while (!DHT11_READ() && timeout) /* 等待高电平到来 */
{
udelay(1);
--timeout;
}
if (!timeout)
{
printk("timeout %d\n", __LINE__);
return-1; /* 超时 */
}
timeout = 1000;
while (DHT11_READ() && timeout) /* 等待高电平结束 */
{
udelay(1);
--timeout;
}
if (!timeout)
{
printk("timeout %d\n", __LINE__);
return-1; /* 超时 */
}
return0;
}
staticintdht11_start(void)
{
DHT11_IO_OUT();
DHT11_WRITE(0);
mdelay(20);
DHT11_WRITE(1);
udelay(30);
DHT11_IO_IN(); /* 设置为输入 */
udelay(2);
if (dht11_wait_for_ready()) return-1;
return0;
}
staticintdht11_read_byte(unsignedchar *byte)
{
unsignedchar i;
unsignedchar bit = 0;
unsignedchar data = 0;
int timeout = 0;
for (i = 0; i < 8; i++)
{
timeout = 1000;
while (DHT11_READ() && timeout) /* 等待变为低电平 */
{
udelay(1);
--timeout;
}
if (!timeout)
{
printk("timeout %d\n", __LINE__);
return-1; /* 超时 */
}
timeout = 1000;
while (!DHT11_READ() && timeout) /* 等待变为高电平 */
{
udelay(1);
--timeout;
}
if (!timeout)
{
printk("timeout %d\n", __LINE__);
return-1; /* 超时 */
}
udelay(40);
bit = DHT11_READ();
data <<= 1;
if (bit)
{
data |= 0x01;
#if 0
timeout = 1000;
while (DHT11_READ() && timeout) /* 等待高电平结束 */
{
udelay(1);
--timeout;
}
if (!timeout)
{
printk("timeout %d\n", __LINE__);
return-1; /* 超时 */
}
#endif
}
// data <<= 1; /* 导致错误的原因 ： 移位要放前面，不能放在这里，若放在后面一旦获取最后一个位就会多移动一位导致数据不对 */
}
*byte = data;
return0;
}
- 这部分就是驱动dht11的代码，和单片机下驱动没有什么区别。
- 在编写读取一个字节的函数时出现谬误 ： data <<= 1，数据移位，不能放到最后，移位要放前面，不能放在这里，若放在后面一旦获取最后一个位就会多移动一位导致数据不对，该谬误导致调试了挺久，开始还以为时序有问题一直检查时序。。。
dht11驱动跟内核框架有关的部分：
/* 使设备只能被一个进程打开 */
staticint _drv_open (struct inode *node, struct file *file)
{
printk("dht11 open\n");
return0;
}
staticssize_t _drv_read(struct file *filp, char __user *buf, size_t size, loff_t *offset)
{
int ret;
int i;
unsignedchar data[5] = {0};
unsignedlong flags;
if (size != 5) return -EINVAL;
/* 关闭中断,防止时序被中断破坏 */
spin_lock_irqsave(&dht11_dev.lock, flags);
/* 启动信号 */
if (dht11_start() != 0)
{
printk("dht11 start failed\n");
ret = -EFAULT;
goto failed1;
}
/* 读出5字节数据 */
for (i = 0; i < 5; i++)
{
if (dht11_read_byte(&data[i]))
{
printk("read data err\n");
ret = -EAGAIN;
goto failed1;
}
}
/* 打开中断 */
spin_unlock_irqrestore(&dht11_dev.lock, flags);
/* 校验数据 */
if (data[4] != (data[0]+data[1]+data[2]+data[3]))
{
printk("check data failed\n");
ret = -EAGAIN;
goto failed1;
}
/* 将数据拷贝回用户空间 */
if (copy_to_user(buf, data, 5))
{
ret = -EFAULT;
}
else
{
ret = 5;
}
return ret;
failed1:
spin_unlock_irqrestore(&dht11_dev.lock, flags);
return ret;
}
staticint _drv_release(struct inode *node, struct file *file)
{
printk("dht11 release\n");
return0;
}
staticstructfile_operationsdrv_file_ops = {
.owner = THIS_MODULE,
.open = _drv_open,
.read = _drv_read,
.release = _drv_release,
};
/* 设备树的匹配列表 */
staticstructof_device_iddts_match_table[] = {
{.compatible = DEV_DTS_COMPATIBLE, }, /* 通过设备树来匹配 */
};
staticint _driver_probe(struct platform_device *pdev)
{
int err;
structdevice *ds_dev;
structdevice_node *dev_node;
structdevice_node *node = pdev->dev.of_node;
if (!node) {
printk("hc-sr501 dts node can not found!\r\n");
return -EINVAL;
}
dev_node = of_find_node_by_path(DEV_DTS_NODE_PATH); /* 找到dht11的设备树节点 */
if (IS_ERR(dev_node)) {
printk("dht11 DTS Node not found!\r\n");
return PTR_ERR(dev_node);
}
dht11_dev.gpio = of_get_named_gpio(dev_node, DEV_PIN_DTS_NAME, 0); /* 获取dht11的gpio编号 */
if ( dht11_dev.gpio < 0) {
printk("dht11-gpio not found!\r\n");
return -EINVAL;
}
err = gpio_request(dht11_dev.gpio, DEV_PIN_DTS_NAME);
if(err)
{
printk("gpio_request gpio is failed!\n");
return -EINVAL;
}
printk("dht11 gpio %d\n", dht11_dev.gpio);
/* 内核自动分配设备号 */
err = alloc_chrdev_region(&dht11_dev.dev_no, 0, 1, DEV_NAME);
if (err < 0) {
pr_err("Error: failed to register mbochs_dev, err: %d\n", err);
goto failed3;
}
cdev_init(&dht11_dev.chrdev, &drv_file_ops);
cdev_add(&dht11_dev.chrdev, dht11_dev.dev_no, 1);
dht11_dev.class = class_create(THIS_MODULE, DEV_NAME);
if (IS_ERR(dht11_dev.class)) {
err = PTR_ERR(dht11_dev.class);
goto failed1;
}
/* 创建设备节点 */
ds_dev = device_create(dht11_dev.class , NULL, dht11_dev.dev_no, NULL, DEV_NAME);
if (IS_ERR(ds_dev)) { /* 判断指针是否合法 */
err = PTR_ERR(ds_dev);
goto failed2;
}
spin_lock_init(&dht11_dev.lock); /* 初始化自旋锁 */
printk("dht11 probe success\r\n");
return0;
failed2:
device_destroy(dht11_dev.class, dht11_dev.dev_no);
class_destroy(dht11_dev.class);
failed1:
unregister_chrdev_region(dht11_dev.dev_no, 1);
cdev_del(&dht11_dev.chrdev);
failed3:
gpio_free(dht11_dev.gpio);
return err;
}
staticint _driver_remove(struct platform_device *pdev)
{
device_destroy(dht11_dev.class, dht11_dev.dev_no);
class_destroy(dht11_dev.class);
unregister_chrdev_region(dht11_dev.dev_no, 1);
cdev_del(&dht11_dev.chrdev);
gpio_free(dht11_dev.gpio);
printk(KERN_INFO"dht11 remove success\n");
return0;
}
staticstructplatform_driver _platform_driver = {
.probe = _driver_probe,
.remove = _driver_remove,
.driver = {
.name = DEV_DTS_COMPATIBLE,
.owner = THIS_MODULE,
.of_match_table = dts_match_table, /* 通过设备树匹配 */
},
};
/* 入口函数 */
staticint __init _driver_init(void)
{
int ret;
printk("dht11 %s\n", __FUNCTION__);
ret = platform_driver_register(&_platform_driver); //注册platform驱动
return ret;
}
/* 出口函数 */
staticvoid __exit _driver_exit(void)
{
printk("dht11 %s\n", __FUNCTION__);
platform_driver_unregister(&_platform_driver);
}
module_init(_driver_init);
module_exit(_driver_exit);
MODULE_AUTHOR("Ares");
MODULE_LICENSE("GPL");
测试程序
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<unistd.h>
#include<stdio.h>
#include<string.h>
#include<sys/ioctl.h>
#include<poll.h>
#include<stdint.h>
#define DEV_NAME "/dev/dht11"
voidsleep_ms(unsignedint ms)
{
structtimevaldelay;
delay.tv_sec = 0;
delay.tv_usec = ms * 1000;
select(0, NULL, NULL, NULL, &delay);
}
intmain(int argc, char **argv)
{
int fd;
int ret;
structpollfdfds[1];
/* 2. 打开文件 */
fd = open(DEV_NAME, O_RDWR); // | O_NONBLOCK
if (fd < 0)
{
printf("can not open file %s, %d\n", DEV_NAME, fd);
return-1;
}
uint8_t dht11_data[5];
while (1)
{
if ((ret = read(fd, dht11_data, sizeof(dht11_data))) == sizeof(dht11_data))
{
printf("temp %d.%d humi %d.%d\r\n", dht11_data[2], dht11_data[3], dht11_data[0], dht11_data[1]);
}
else
{
printf("get temp err %d\r\n", ret);
}
sleep_ms(500);
}
}
中断方式
通过编写调试发现通过中断方式很难实现，由于linux的非实时性，中断会丢失，会导致时序不对。
内核中自带的dht11驱动使用IIO子系统实现
drivers/iio/humidity/dht11.c
内核配置：
编写设备树参考Documentation\devicetree\bindings\iio\humidity\dht11.txt
* DHT11 humidity/temperature sensor(and compatibles like DHT22)
Required properties:
- compatible: Should be "dht11"
- gpios: Should specify the GPIO connected to the sensor's data
line, see "gpios property" in
Documentation/devicetree/bindings/gpio/gpio.txt.
Example:
humidity_sensor {
compatible = "dht11";
gpios = <&gpio0 60>;
}
- 若要使用内核dht11驱动，只要在设备树中添加
compatible = "dht11"
