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Add a DHT11 Sensor Driver Example Using GPIO
Use GPIO to communicate with the DHT11 sensor. Test detail: - Tested on Raspberry Pi 5B with Raspberry Pi OS (Debian 12, Linux version 6.6.74) - Verify that the DHT11 driver compiles and loads successfully - Verify that temperature and humidity data can be read correctly from the DHT11 sensor
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‎.ci/non-working

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@@ -4,3 +4,4 @@ intrpt
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vkbd
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syscall-steal
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led
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dht11

‎examples/Makefile

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@@ -32,6 +32,7 @@ obj-m += vinput.o
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obj-m += vkbd.o
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obj-m += static_key.o
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obj-m += led.o
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obj-m += dht11.o
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PWD := $(CURDIR)
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‎examples/dht11.c

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/*
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* dht11.c - Using GPIO to read temperature and humidity from DHT11 sensor.
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*/
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#include <linux/cdev.h>
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#include <linux/delay.h>
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#include <linux/device.h>
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#include <linux/fs.h>
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#include <linux/gpio.h>
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#include <linux/init.h>
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#include <linux/module.h>
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#include <linux/printk.h>
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#include <linux/types.h>
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#include <linux/uaccess.h>
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#include <linux/version.h>
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#include <asm/errno.h>
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#define GPIO_PIN_4 575
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#define DEVICE_NAME "dht11"
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#define DEVICE_CNT 1
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static char msg[64];
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struct dht11_dev {
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dev_t dev_num;
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int major_num, minor_num;
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struct cdev cdev;
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struct class *cls;
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struct device *dev;
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};
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static struct dht11_dev dht11_device;
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/* Define GPIOs for LEDs.
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* TODO: According to the requirements, search /sys/kernel/debug/gpio to
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* find the corresponding GPIO location.
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*/
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static struct gpio dht11[] = { { GPIO_PIN_4, GPIOF_OUT_INIT_HIGH, "Signal" } };
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static int dht11_read_data(void)
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{
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int timeout;
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uint8_t sensor_data[5] = { 0 };
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uint8_t i, j;
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gpio_set_value(dht11[0].gpio, 0);
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mdelay(20);
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gpio_set_value(dht11[0].gpio, 1);
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udelay(30);
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gpio_direction_input(dht11[0].gpio);
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udelay(2);
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timeout = 300;
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while (gpio_get_value(dht11[0].gpio) && timeout--)
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udelay(1);
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if (timeout == 0) {
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return -ETIMEDOUT;
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}
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timeout = 300;
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while (!gpio_get_value(dht11[0].gpio) && timeout--)
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udelay(1);
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if (timeout == 0) {
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return -ETIMEDOUT;
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}
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timeout = 300;
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while (gpio_get_value(dht11[0].gpio) && timeout--)
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udelay(1);
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if (timeout == 0) {
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return -ETIMEDOUT;
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}
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for (j = 0; j < 5; j++) {
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uint8_t byte = 0;
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for (i = 0; i < 8; i++) {
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timeout = 300;
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while (gpio_get_value(dht11[0].gpio) && timeout--)
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udelay(1);
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if (timeout == 0) {
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return -ETIMEDOUT;
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}
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timeout = 300;
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while (!gpio_get_value(dht11[0].gpio) && timeout--)
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udelay(1);
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if (timeout == 0) {
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return -ETIMEDOUT;
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}
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udelay(50);
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byte <<= 1;
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if (gpio_get_value(dht11[0].gpio))
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byte |= 0x01;
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}
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sensor_data[j] = byte;
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}
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if (sensor_data[4] != (uint8_t)(sensor_data[0] + sensor_data[1] +
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sensor_data[2] + sensor_data[3]))
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return -EIO;
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gpio_direction_output(dht11[0].gpio, 1);
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sprintf(msg, "Humidity: %d%%\nTemperature: %d deg C\n", sensor_data[0],
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sensor_data[2]);
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return 0;
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}
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static int device_open(struct inode *inode, struct file *file)
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{
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int ret, retry;
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for (retry = 0; retry < 5; ++retry) {
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ret = dht11_read_data();
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if (ret == 0)
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return 0;
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msleep(10);
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}
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if (ret) {
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gpio_direction_output(dht11[0].gpio, 1);
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return ret;
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}
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return 0;
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}
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static int device_release(struct inode *inode, struct file *file)
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{
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return 0;
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}
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static ssize_t device_read(struct file *filp, char __user *buffer,
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size_t length, loff_t *offset)
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{
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int msg_len = strlen(msg);
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if (*offset >= msg_len)
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return 0;
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size_t remain = msg_len - *offset;
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size_t bytes_read = min(length, remain);
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if (copy_to_user(buffer, msg + *offset, bytes_read))
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return -EFAULT;
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*offset += bytes_read;
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return bytes_read;
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}
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static struct file_operations fops = {
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#if LINUX_VERSION_CODE < KERNEL_VERSION(6, 4, 0)
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.owner = THIS_MODULE,
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#endif
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.open = device_open,
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.release = device_release,
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.read = device_read
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};
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/* Initialize the module - Register the character device */
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static int __init dht11_init(void)
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{
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int ret = 0;
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/* Determine whether dynamic allocation of the device number is needed. */
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if (dht11_device.major_num) {
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dht11_device.dev_num =
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MKDEV(dht11_device.major_num, dht11_device.minor_num);
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ret = register_chrdev_region(dht11_device.dev_num, DEVICE_CNT,
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DEVICE_NAME);
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} else {
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ret = alloc_chrdev_region(&dht11_device.dev_num, 0, DEVICE_CNT,
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DEVICE_NAME);
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}
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/* Negative values signify an error */
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if (ret < 0) {
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pr_alert("Failed to register character device, error: %d\n", ret);
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return ret;
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}
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pr_info("Major = %d, Minor = %d\n", MAJOR(dht11_device.dev_num),
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MINOR(dht11_device.dev_num));
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/* Prevents module unloading while operations are in use */
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#if LINUX_VERSION_CODE < KERNEL_VERSION(6, 4, 0)
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dht11_device.cdev.owner = THIS_MODULE;
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#endif
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cdev_init(&dht11_device.cdev, &fops);
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ret = cdev_add(&dht11_device.cdev, dht11_device.dev_num, 1);
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if (ret) {
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pr_err("Failed to add the device to the system\n");
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goto fail1;
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}
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#if LINUX_VERSION_CODE >= KERNEL_VERSION(6, 4, 0)
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dht11_device.cls = class_create(DEVICE_NAME);
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#else
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dht11_device.cls = class_create(THIS_MODULE, DEVICE_NAME);
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#endif
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if (IS_ERR(dht11_device.cls)) {
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pr_err("Failed to create class for device\n");
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ret = PTR_ERR(dht11_device.cls);
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goto fail2;
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}
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dht11_device.dev = device_create(dht11_device.cls, NULL,
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dht11_device.dev_num, NULL, DEVICE_NAME);
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if (IS_ERR(dht11_device.dev)) {
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pr_err("Failed to create the device file\n");
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ret = PTR_ERR(dht11_device.dev);
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goto fail3;
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}
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pr_info("Device created on /dev/%s\n", DEVICE_NAME);
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ret = gpio_request(dht11[0].gpio, dht11[0].label);
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if (ret) {
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pr_err("Unable to request GPIOs for dht11: %d\n", ret);
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goto fail4;
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}
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ret = gpio_direction_output(dht11[0].gpio, 1);
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if (ret) {
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pr_err("Failed to set GPIO %d direction\n", dht11[0].gpio);
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goto fail5;
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}
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return 0;
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fail5:
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gpio_free(dht11[0].gpio);
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fail4:
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device_destroy(dht11_device.cls, dht11_device.dev_num);
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fail3:
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class_destroy(dht11_device.cls);
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fail2:
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cdev_del(&dht11_device.cdev);
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fail1:
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unregister_chrdev_region(dht11_device.dev_num, DEVICE_CNT);
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return ret;
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}
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static void __exit dht11_exit(void)
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{
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gpio_set_value(dht11[0].gpio, 0);
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gpio_free(dht11[0].gpio);
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device_destroy(dht11_device.cls, dht11_device.dev_num);
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class_destroy(dht11_device.cls);
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cdev_del(&dht11_device.cdev);
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unregister_chrdev_region(dht11_device.dev_num, DEVICE_CNT);
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}
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module_init(dht11_init);
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module_exit(dht11_exit);
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MODULE_LICENSE("GPL");

‎lkmpg.tex

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@@ -1933,6 +1933,41 @@ \subsection{Control the LED's on/off state}
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sudo rmmod led
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\end{codebash}
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\subsection{DHT11 sensor}
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\label{sec:gpio_dht11}
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The DHT11 sensor is a well-known entry-level sensor commonly used to measure humidity and temperature.
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In this subsection, we will use GPIO to communicate through a single data line.
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The DHT11 communication protocol can be referred to in the \href{https://www.mouser.com/datasheet/2/758/DHT11-Technical-Data-Sheet-Translated-Version-1143054.pdf?srsltid=AfmBOoppls-QTd864640bVtbK90sWBsFzJ_7SgjOD2EpwuLLGUSTyYnv}{datasheet}.
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In the implementation, the data pin of the DHT11 sensor is connected to GPIO4 on the Raspberry Pi.
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The sensor's VCC and GND pins are connected to 3.3V and GND, respectively.
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For more details about the Raspberry Pi pin assignments, refer to \href{https://pinout.xyz/}{Raspberry Pi Pinout}.
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The materials used include a Raspberry Pi 5, a DHT11 sensor, and jumper wires.
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\samplec{examples/dht11.c}
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Make and install the module:
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\begin{codebash}
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make
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sudo insmod dht11.ko
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\end{codebash}
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Check the Output of the DHT11 Sensor:
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\begin{codebash}
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sudo cat /dev/dht11
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\end{codebash}
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Expected Output:
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\begin{verbatim}
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$ sudo cat /dev/dht11
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Humidity: 61%
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Temperature: 30°C
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\end{verbatim}
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Finally, remove the module:
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\begin{codebash}
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sudo rmmod dht11
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\end{codebash}
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19361971
\section{Scheduling Tasks}
19371972
\label{sec:scheduling_tasks}
19381973
There are two main ways of running tasks: tasklets and work queues.

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