经验分享—— Linux 内核驱动 DHT11 温湿度传感器

[i=s] 本帖最后由 paopiu 于 2023-11-8 08:47 编辑 [/i]<br /> <br /> **Linux** 内核中自带的 **DHT11** 驱动使用IIO子系统实现。今天给大家介绍直接使用默认 **DHT11** 驱动的方式读取温湿度。本文以 **LuckFox Pico** 为例，撰写教程。 ### 1. 修改内核 切换到内核目录下，并修改内核配置 ``` cd /home/luckfox/Luckfox-Pico/luckfox-pico/sysdrv/source/kernel cp ./arch/arm/configs/luckfox_rv1106_linux_defconfig .config make ARCH=arm menuconfig ``` 在打开的页面中搜索 **DHT11** 或者也可以按 **↑ ↓ \<Select\>** 依次选择 **> Device Drivers > Industrial I/O support > Humidity sensors > DHT11 (and compatible sensors) driver** ) 按下 `/` 搜索，输入 **DHT11** ) 回车，就跳到 **DHT11** 简介页面了 ) 按下数字 **1** ，跳到使能 **DHT11** 页面 ) 按下 **Y** ，打开使能。 选择 **<Save>** 保存配置文件 ) ) 复制配置 ``` make ARCH=arm savedefconfig cp defconfig ./arch/arm/configs/luckfox_rv1106_linux_defconfig ``` 其实这个驱动源代码可以在 **SDK** 里找到 ``` cat /home/luckfox/Luckfox-Pico/luckfox-pico/sysdrv/source/kernel/drivers/iio/humidity/dht11.c ``` 完整的内核可以在 **GitHub** 上找到 [dht11.c]([https://github.com/torvalds/linux/blob/master/drivers/iio/humidity/dht11.c](https://github.com/torvalds/linux/blob/master/drivers/iio/humidity/dht11.c)) ###### dht11.c ``` // SPDX-License-Identifier: GPL-2.0-or-later /* * DHT11/DHT22 bit banging GPIO driver * * Copyright (c) Harald Geyer <[email]harald@ccbib.org[/email]> */ #include <linux/err.h> #include <linux/interrupt.h> #include <linux/device.h> #include <linux/kernel.h> #include <linux/printk.h> #include <linux/slab.h> #include <linux/of.h> #include <linux/of_device.h> #include <linux/sysfs.h> #include <linux/io.h> #include <linux/module.h> #include <linux/platform_device.h> #include <linux/wait.h> #include <linux/bitops.h> #include <linux/completion.h> #include <linux/mutex.h> #include <linux/delay.h> #include <linux/gpio/consumer.h> #include <linux/timekeeping.h> #include <linux/iio/iio.h> #define DRIVER_NAME "dht11" #define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */ #define DHT11_EDGES_PREAMBLE 2 #define DHT11_BITS_PER_READ 40 /* * Note that when reading the sensor actually 84 edges are detected, but * since the last edge is not significant, we only store 83: */ #define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \ DHT11_EDGES_PREAMBLE + 1) /* * Data transmission timing: * Data bits are encoded as pulse length (high time) on the data line. * 0-bit: 22-30uS -- typically 26uS (AM2302) * 1-bit: 68-75uS -- typically 70uS (AM2302) * The acutal timings also depend on the properties of the cable, with * longer cables typically making pulses shorter. * * Our decoding depends on the time resolution of the system: * timeres > 34uS ... don't know what a 1-tick pulse is * 34uS > timeres > 30uS ... no problem (30kHz and 32kHz clocks) * 30uS > timeres > 23uS ... don't know what a 2-tick pulse is * timeres < 23uS ... no problem * * Luckily clocks in the 33-44kHz range are quite uncommon, so we can * support most systems if the threshold for decoding a pulse as 1-bit * is chosen carefully. If somebody really wants to support clocks around * 40kHz, where this driver is most unreliable, there are two options. * a) select an implementation using busy loop polling on those systems * b) use the checksum to do some probabilistic decoding */ #define DHT11_START_TRANSMISSION_MIN 18000 /* us */ #define DHT11_START_TRANSMISSION_MAX 20000 /* us */ #define DHT11_MIN_TIMERES 34000 /* ns */ #define DHT11_THRESHOLD 49000 /* ns */ #define DHT11_AMBIG_LOW 23000 /* ns */ #define DHT11_AMBIG_HIGH 30000 /* ns */ struct dht11 { struct device *dev; struct gpio_desc *gpiod; int irq; struct completion completion; /* The iio sysfs interface doesn't prevent concurrent reads: */ struct mutex lock; s64 timestamp; int temperature; int humidity; /* num_edges: -1 means "no transmission in progress" */ int num_edges; struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ]; }; #ifdef CONFIG_DYNAMIC_DEBUG /* * dht11_edges_print: show the data as actually received by the * driver. */ static void dht11_edges_print(struct dht11 *dht11) { int i; dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges); for (i = 1; i < dht11->num_edges; ++i) { dev_dbg(dht11->dev, "%d: %lld ns %s\n", i, dht11->edges[i].ts - dht11->edges[i - 1].ts, dht11->edges[i - 1].value ? "high" : "low"); } } #endif /* CONFIG_DYNAMIC_DEBUG */ static unsigned char dht11_decode_byte(char *bits) { unsigned char ret = 0; int i; for (i = 0; i < 8; ++i) { ret <<= 1; if (bits[i]) ++ret; } return ret; } static int dht11_decode(struct dht11 *dht11, int offset) { int i, t; char bits[DHT11_BITS_PER_READ]; unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum; for (i = 0; i < DHT11_BITS_PER_READ; ++i) { t = dht11->edges[offset + 2 * i + 2].ts - dht11->edges[offset + 2 * i + 1].ts; if (!dht11->edges[offset + 2 * i + 1].value) { dev_dbg(dht11->dev, "lost synchronisation at edge %d\n", offset + 2 * i + 1); return -EIO; } bits[i] = t > DHT11_THRESHOLD; } hum_int = dht11_decode_byte(bits); hum_dec = dht11_decode_byte(&bits[8]); temp_int = dht11_decode_byte(&bits[16]); temp_dec = dht11_decode_byte(&bits[24]); checksum = dht11_decode_byte(&bits[32]); if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) { dev_dbg(dht11->dev, "invalid checksum\n"); return -EIO; } dht11->timestamp = ktime_get_boottime_ns(); if (hum_int < 4) { /* DHT22: 100000 = (3*256+232)*100 */ dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) * ((temp_int & 0x80) ? -100 : 100); dht11->humidity = ((hum_int << 8) + hum_dec) * 100; } else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */ dht11->temperature = temp_int * 1000; dht11->humidity = hum_int * 1000; } else { dev_err(dht11->dev, "Don't know how to decode data: %d %d %d %d\n", hum_int, hum_dec, temp_int, temp_dec); return -EIO; } return 0; } /* * IRQ handler called on GPIO edges */ static irqreturn_t dht11_handle_irq(int irq, void *data) { struct iio_dev *iio = data; struct dht11 *dht11 = iio_priv(iio); if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) { dht11->edges[dht11->num_edges].ts = ktime_get_boottime_ns(); dht11->edges[dht11->num_edges++].value = gpiod_get_value(dht11->gpiod); if (dht11->num_edges >= DHT11_EDGES_PER_READ) complete(&dht11->completion); } return IRQ_HANDLED; } static int dht11_read_raw(struct iio_dev *iio_dev, const struct iio_chan_spec *chan, int *val, int *val2, long m) { struct dht11 *dht11 = iio_priv(iio_dev); int ret, timeres, offset; mutex_lock(&dht11->lock); if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boottime_ns()) { timeres = ktime_get_resolution_ns(); dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres); if (timeres > DHT11_MIN_TIMERES) { dev_err(dht11->dev, "timeresolution %dns too low\n", timeres); /* In theory a better clock could become available * at some point ... and there is no error code * that really fits better. */ ret = -EAGAIN; goto err; } if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH) dev_warn(dht11->dev, "timeresolution: %dns - decoding ambiguous\n", timeres); reinit_completion(&dht11->completion); dht11->num_edges = 0; ret = gpiod_direction_output(dht11->gpiod, 0); if (ret) goto err; usleep_range(DHT11_START_TRANSMISSION_MIN, DHT11_START_TRANSMISSION_MAX); ret = gpiod_direction_input(dht11->gpiod); if (ret) goto err; ret = request_irq(dht11->irq, dht11_handle_irq, IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, iio_dev->name, iio_dev); if (ret) goto err; ret = wait_for_completion_killable_timeout(&dht11->completion, HZ); free_irq(dht11->irq, iio_dev); #ifdef CONFIG_DYNAMIC_DEBUG dht11_edges_print(dht11); #endif if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) { dev_err(dht11->dev, "Only %d signal edges detected\n", dht11->num_edges); ret = -ETIMEDOUT; } if (ret < 0) goto err; offset = DHT11_EDGES_PREAMBLE + dht11->num_edges - DHT11_EDGES_PER_READ; for (; offset >= 0; --offset) { ret = dht11_decode(dht11, offset); if (!ret) break; } if (ret) goto err; } ret = IIO_VAL_INT; if (chan->type == IIO_TEMP) *val = dht11->temperature; else if (chan->type == IIO_HUMIDITYRELATIVE) *val = dht11->humidity; else ret = -EINVAL; err: dht11->num_edges = -1; mutex_unlock(&dht11->lock); return ret; } static const struct iio_info dht11_iio_info = { .read_raw = dht11_read_raw, }; static const struct iio_chan_spec dht11_chan_spec[] = { { .type = IIO_TEMP, .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }, { .type = IIO_HUMIDITYRELATIVE, .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), } }; static const struct of_device_id dht11_dt_ids[] = { { .compatible = "dht11", }, { } }; MODULE_DEVICE_TABLE(of, dht11_dt_ids); static int dht11_probe(struct platform_device *pdev) { struct device *dev = &pdev->dev; struct dht11 *dht11; struct iio_dev *iio; iio = devm_iio_device_alloc(dev, sizeof(*dht11)); if (!iio) { dev_err(dev, "Failed to allocate IIO device\n"); return -ENOMEM; } dht11 = iio_priv(iio); dht11->dev = dev; dht11->gpiod = devm_gpiod_get(dev, NULL, GPIOD_IN); if (IS_ERR(dht11->gpiod)) return PTR_ERR(dht11->gpiod); dht11->irq = gpiod_to_irq(dht11->gpiod); if (dht11->irq < 0) { dev_err(dev, "GPIO %d has no interrupt\n", desc_to_gpio(dht11->gpiod)); return -EINVAL; } dht11->timestamp = ktime_get_boottime_ns() - DHT11_DATA_VALID_TIME - 1; dht11->num_edges = -1; platform_set_drvdata(pdev, iio); init_completion(&dht11->completion); mutex_init(&dht11->lock); iio->name = pdev->name; iio->info = &dht11_iio_info; iio->modes = INDIO_DIRECT_MODE; iio->channels = dht11_chan_spec; iio->num_channels = ARRAY_SIZE(dht11_chan_spec); return devm_iio_device_register(dev, iio); } static struct platform_driver dht11_driver = { .driver = { .name = DRIVER_NAME, .of_match_table = dht11_dt_ids, }, .probe = dht11_probe, }; module_platform_driver(dht11_driver); MODULE_AUTHOR("Harald Geyer <[email]harald@ccbib.org[/email]>"); MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver"); MODULE_LICENSE("GPL v2"); ``` ### 2. 修改设备树 设备树的修改也很简单。其他 **Linux** 内核的设备树引脚可能略有不同。**Linux** 完整设备树可以参考 **Github** [设备树]([https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/iio/humidity/dht11.yaml](https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/iio/humidity/dht11.yaml)) ``` vi /home/luckfox/Luckfox-Pico/luckfox-pico/sysdrv/source/kernel/arch/arm/boot/dts/rv1103g-luckfox-pico.dts ``` 在 `compatible = "rockchip,rv1103g-38x38-ipc-v10", "rockchip,rv1103";` 这一行下面新增 `humidity_sensor` ，关于这个 `gpios` ，可以看官方引脚图， **RK_P** 是固定的。比如你想使用 **58** 号引脚，那就是 **RK_PD2** 。如果有其他设备树描述涉及到了这个引脚，记得注释掉，防止冲突。 ) ###### rv1103g-luckfox-pico.dts ``` humidity_sensor { compatible = "dht11"; gpios = <&gpio1 RK_PC7 GPIO_ACTIVE_HIGH>; // GPIO pin for DHT11 data }; ``` ### 3. 编译内核 切换到编译目录 ``` cd /home/luckfox/Luckfox-Pico/luckfox-pico ``` 选择编译分支， **LuckFox Pico** 按 **0** ``` ./build.sh lunch ``` 最后编译内核 ``` ./build.sh kernel ``` 内核编译成功后生成的文件在 `<SDK目录>output/image` 目录下，替换原固件中的 `boot.image` 与 `env.txt` 文件。使用 SocToolKit 重新创建SD。 ### 4. 编译传感器读取代码 ###### Makefile ``` # 指定架构 ARCH=arm # 指定编译工具链 CROSS_COMPILE=/home/luckfox/Luckfox-Pico/luckfox-pico/tools/linux/toolchain/arm-rockchip830-linux-uclibcgnueabihf/bin/arm-rockchip830-linux-uclibcgnueabihf- export ARCH CROSS_COMPILE name=humidity_sensor PWD?=$(shell pwd) all: $(CROSS_COMPILE)gcc $(name).c -o $(name) echo $(PWD) clean: rm -f *.ko *.o *.mod *.mod.o *.mod.c *.symvers *.order *.cmd obj-m += $(name).o ``` ###### humidity_sensor.c ``` #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <fcntl.h> #include <errno.h> int main(void) { int temp_fd, humidity_fd; char temp_buf[32], humidity_buf[32]; int temp, humidity; temp_fd = open("/sys/bus/iio/devices/iio:device1/in_temp_input", O_RDONLY); humidity_fd = open("/sys/bus/iio/devices/iio:device1/in_humidityrelative_input", O_RDONLY); if (temp_fd == -1 || humidity_fd == -1) { perror("Failed to open sensor data files"); exit(-1); } while (1) { // Read temperature data lseek(temp_fd, 0, SEEK_SET); ssize_t temp_size = read(temp_fd, temp_buf, sizeof(temp_buf) - 1); if (temp_size == -1) { perror("Failed to read temperature data"); exit(-1); } temp_buf[temp_size] = '\0'; temp = atoi(temp_buf); // Read humidity data lseek(humidity_fd, 0, SEEK_SET); ssize_t humidity_size = read(humidity_fd, humidity_buf, sizeof(humidity_buf) - 1); if (humidity_size == -1) { perror("Failed to read humidity data"); exit(-1); } humidity_buf[humidity_size] = '\0'; humidity = atoi(humidity_buf); // Convert to float float temp_float = (float)temp / 1000; float humidity_float = (float)humidity / 1000; printf("Temperature: %.1f C, Humidity: %.1f %%RH\n", temp_float, humidity_float); sleep(1); } close(temp_fd); close(humidity_fd); return 0; } ``` 使用 `make` 命令编译代码，并将编译好的 `humidity_sensor` 上传到开发板。 在开发板中，执行 `humidity_sensor` ``` chmod +x humidity_sensor ./humidity_sensor ``` ) 如果你的结果和我一样，说明这个 **DHT11** 已经不准了，温度小数位也返回了值。可以执行 `dmesg` 查看日志。 ``` dmesg ``` ) 如果对精度要求不高，可以试着修改 `dht.c` 驱动的第 **156** 行，判断小数位的代码，并重新编译内核并烧录。

学习一下

学习了,以后我就是老师的枪,老师让我打哪我就打哪

打卡学习~

就要这样多元化发展

学习学习

大佬牛，学习一下