# dht11
用rpi來演練
dht11 linux driver: https://github.com/torvalds/linux/blob/master/drivers/iio/humidity/dht11.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * DHT11/DHT22 bit banging GPIO driver
 *
 * Copyright (c) Harald Geyer <[e-mail]>
 */

#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/sysfs.h>
#include <linux/io.h>
#include <linux/mod_devicetable.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 <[e-mail]>");
MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
MODULE_LICENSE("GPL v2");

在我的pi中已經存在，沒有的話需要交叉編譯並且安裝對應的driver

$ modinfo dht11
filename:       /lib/modules/6.6.74+rpt-rpi-v8/kernel/drivers/iio/humidity/dht11.ko.xz
license:        GPL v2
description:    DHT11 humidity/temperature sensor driver
author:         Harald Geyer <[e-mail]>
srcversion:     3D799035BD55AA9516D1306
alias:          of:N*T*Cdht11C*
alias:          of:N*T*Cdht11
depends:        industrialio
intree:         Y
name:           dht11
vermagic:       6.6.74+rpt-rpi-v8 SMP preempt mod_unload modversions aarch64
$ modprobe dht11
$ lsmod | grep dht11
dht11                  12288  0
industrialio           98304  2 iio_hwmon,dht11

### 透過device tree讀取溫濕度

sudo vim /boot/config.txt
# add the following line to the bottom
dtoverlay=dht11,gpiopin=4

重啟，確認Device driver有沒有正確掛載

ls /sys/bus/iio/devices/
iio:device0
cat /sys/bus/iio/devices/iio:device0/name
dht11

接著就可以直接讀取溫濕度

cat /sys/bus/iio/devices/iio:device0/in_temp_input
22300
cat /sys/bus/iio/devices/iio:device0/in_humidityrelative_input
55000

22300代表22.3^。^C, 55000代表濕度為55%
寫成bash script，可以直接呼叫

#!/bin/bash
while true; do
  TEMP=$(cat /sys/bus/iio/devices/iio:device0/in_temp_input)
  HUMID=$(cat /sys/bus/iio/devices/iio:device0/in_humidityrelative_input)
  echo "Temperature: $(echo "scale=1; $TEMP / 1000" | bc)°C"
  echo "Humidity: $(echo "scale=1; $HUMID / 1000" | bc)%"
  sleep 2
done

:::info
DHT11只是個玩具Sensor，讀出來的數據當作參考就好，我主要用在自幹的pi-nas上來遠端觀察系統運行時的環境溫度。
:::

# Appendix
* [Cross compile the rpi-kernel](https://www.raspberrypi.com/documentation/computers/linux_kernel.html)
dht11可以在Device dirver->iio->humidity->dht11中找到
* WiringPi有gpio readall
* https://github.com/WiringPi/WiringPi/releases

gpio readall
 +-----+-----+---------+------+---+---Pi 4B--+---+------+---------+-----+-----+
 | BCM | wPi |   Name  | Mode | V | Physical | V | Mode | Name    | wPi | BCM |
 +-----+-----+---------+------+---+----++----+---+------+---------+-----+-----+
 |     |     |    3.3v |      |   |  1 || 2  |   |      | 5v      |     |     |
 |   2 |   8 |   SDA.1 |   IN | 1 |  3 || 4  |   |      | 5v      |     |     |
 |   3 |   9 |   SCL.1 |   IN | 1 |  5 || 6  |   |      | 0v      |     |     |
 |   4 |   7 | GPIO. 7 |   IN | 1 |  7 || 8  | 1 | IN   | TxD     | 15  | 14  |
 |     |     |      0v |      |   |  9 || 10 | 1 | IN   | RxD     | 16  | 15  |
 |  17 |   0 | GPIO. 0 |   IN | 0 | 11 || 12 | 0 | IN   | GPIO. 1 | 1   | 18  |
 |  27 |   2 | GPIO. 2 |   IN | 0 | 13 || 14 |   |      | 0v      |     |     |
 |  22 |   3 | GPIO. 3 |   IN | 0 | 15 || 16 | 0 | IN   | GPIO. 4 | 4   | 23  |
 |     |     |    3.3v |      |   | 17 || 18 | 0 | IN   | GPIO. 5 | 5   | 24  |
 |  10 |  12 |    MOSI |   IN | 0 | 19 || 20 |   |      | 0v      |     |     |
 |   9 |  13 |    MISO |   IN | 0 | 21 || 22 | 0 | IN   | GPIO. 6 | 6   | 25  |
 |  11 |  14 |    SCLK |   IN | 0 | 23 || 24 | 1 | IN   | CE0     | 10  | 8   |
 |     |     |      0v |      |   | 25 || 26 | 1 | IN   | CE1     | 11  | 7   |
 |   0 |  30 |   SDA.0 |   IN | 1 | 27 || 28 | 1 | IN   | SCL.0   | 31  | 1   |
 |   5 |  21 | GPIO.21 |   IN | 1 | 29 || 30 |   |      | 0v      |     |     |
 |   6 |  22 | GPIO.22 |   IN | 1 | 31 || 32 | 0 | IN   | GPIO.26 | 26  | 12  |
 |  13 |  23 | GPIO.23 |   IN | 0 | 33 || 34 |   |      | 0v      |     |     |
 |  19 |  24 | GPIO.24 |   IN | 0 | 35 || 36 | 0 | IN   | GPIO.27 | 27  | 16  |
 |  26 |  25 | GPIO.25 |   IN | 0 | 37 || 38 | 0 | IN   | GPIO.28 | 28  | 20  |
 |     |     |      0v |      |   | 39 || 40 | 0 | IN   | GPIO.29 | 29  | 21  |
 +-----+-----+---------+------+---+----++----+---+------+---------+-----+-----+
 | BCM | wPi |   Name  | Mode | V | Physical | V | Mode | Name    | wPi | BCM |
 +-----+-----+---------+------+---+---Pi 4B--+---+------+---------+-----+-----+