02.1_iio_buffer的核心要素与体验

IMX6ULL/doc_pic/14_IIO/02_iio_buffer的使用.md

@@ -9,9 +9,83 @@ IIO(Industrial I/O)参考资料：
 
 
 
-## 1. 驱动框架
+## 1. iio_buffer的核心要素与体验
+
+### 1.1 问题引入
+
+以DHT11为例，读取`/sys/bus/iio/devices/iio:device2/in_temp_input`时，读一次得到一个数据。如果想得到连续的数据，就要使用iio_buffer：
+
+* 驱动程序内部读取多次数据，把数据存在iio_buffer里
+* APP读取/dev/iio:deviceX节点，可以一次读到多个数据
+
+![image-20241107103530226](pic/image-20241107103530226.png)
+
+
+
+以DHT11为例，它有2个通道：温度、湿度，那么读取到的数据格式是怎样的？有如下4种组合：
+
+![image-20241107115503773](pic/image-20241107115503773.png)
+
+
+
+使用iio_buffer读数据时，APP要解决这些问题：
+
+* 只想读温度或湿度，或者想同时读取温度和湿度，怎么设置？
+* 读到的数据里，怎么分辨哪些是温度、哪些是湿度？
+
+驱动程序把数据存入iio_buffer时，驱动要解决这些问题：
+
+* 怎么向APP表示数据的格式：比如温度占据多少bit数据、湿度占据多少bit数据
+
+
+
+### 1.2 数据如何排列
+
+在驱动程序里，对于每个通道，数据的格式如下描述：
+
+![image-20241106185855617](pic/image-20241106185855617.png)
+
+
+
+对于APP，可以如下操作看到这些：
+
+![image-20241106193719202](pic/image-20241106193719202.png)
+
+
+
+### 1.3 如何使能/禁止某个通道
+
+![image-20241106192827693](pic/image-20241106192827693.png)
+
+
+
+### 1.4 如何使能/禁止iio_buffer
+
+![image-20241107110425775](pic/image-20241107110425775.png)
+
+
+
+### 1.5 如何读取buffer
+
+读取设备节点即可，比如：
+
+```shell
+hexdump /dev/iio\:device2
+```
+
+注意：hexdump读到16个字节的数据才会打印出来，如果看到打印缓慢，这是正常的。
+
+
+
+### 1.6 上机体验
+
+![image-20241107110327591](pic/image-20241107110327591.png)
+
+
+
+## 2. 使用iio_buffer的DHT11驱动
+
 
-![image-20241025100410862](pic/image-20241025100410862.png)
 
 
 
@@ -50,6 +124,24 @@ iio_channel_start_all_cb > iio_update_buffers > __iio_update_buffers  > iio_enab
 
 
 
+#### 1.1 iio_buffer细节
+
+```shell
+echo 1 > /sys/bus/iio/devices/iio:device2/buffer/enable
+iio_buffer_store_enable
+    __iio_update_buffers
+        iio_buffer_request_update
+            iio_buffer_update_bytes_per_datum
+                buffer->access->set_bytes_per_datum(buffer, bytes);
+                    iio_set_bytes_per_datum_kfifo
+                        r->bytes_per_datum = bpd;
+             ret = buffer->access->request_update(buffer);
+```
+
+
+
+
+
 ### 2. 从硬件中断到APP
 
 

IMX6ULL/source/14_iio/01_dht11_iio_buffer_software/dht11.c

@@ -0,0 +1,522 @@
+/*
+ * DHT11/DHT22 bit banging GPIO driver
+ *
+ * Copyright (c) Harald Geyer <harald@ccbib.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ */
+
+#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.h>
+#include <linux/of_gpio.h>
+#include <linux/timekeeping.h>
+
+#include <linux/iio/iio.h>
+#include <linux/iio/buffer.h>
+#include <linux/iio/kfifo_buf.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;
+
+	int				gpio;
+	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];
+	struct delayed_work		work;
+	struct iio_dev *iio;
+};
+
+#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_boot_ns();
+	if (hum_int < 20) {  /* DHT22 */
+		dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
+					((temp_int & 0x80) ? -100 : 100);
+		dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
+	} else  {
+		dht11->temperature = temp_int;
+		dht11->humidity = hum_int;
+	}
+
+	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);
+
+	/* TODO: Consider making the handler safe for IRQ sharing */
+	if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
+		dht11->edges[dht11->num_edges].ts = ktime_get_boot_ns();
+		dht11->edges[dht11->num_edges++].value =
+						gpio_get_value(dht11->gpio);
+
+		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_boot_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 = gpio_direction_output(dht11->gpio, 0);
+		if (ret)
+			goto err;
+		usleep_range(DHT11_START_TRANSMISSION_MIN,
+			     DHT11_START_TRANSMISSION_MAX);
+		ret = gpio_direction_input(dht11->gpio);
+		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 = {
+	.driver_module		= THIS_MODULE,
+	.read_raw		= dht11_read_raw,
+};
+
+static const struct iio_chan_spec dht11_chan_spec[] = {
+	{ .type = IIO_TEMP,
+		.scan_index = 0,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), 
+		.scan_type = {
+			.sign = 's',
+			.realbits = 8,
+			.storagebits = 8,
+		},
+	},
+	{ .type = IIO_HUMIDITYRELATIVE,
+		.scan_index = 1,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), 
+		.scan_type = {
+			.sign = 's',
+			.realbits = 8,
+			.storagebits = 8,
+		},
+	}
+};
+
+static const unsigned long dht11_scan_masks[] = {0x3, 0};
+
+static const struct of_device_id dht11_dt_ids[] = {
+	{ .compatible = "dht11", },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, dht11_dt_ids);
+
+static int dht11_iio_buffer_preenable(struct iio_dev *indio_dev)
+{
+	return 0;
+}
+
+static int dht11_iio_buffer_postenable(struct iio_dev *indio_dev)
+{
+	struct dht11 *dht11 = iio_priv(indio_dev);
+
+ 	schedule_delayed_work(&dht11->work, HZ*5);
+	
+	return 0;
+}
+
+static int dht11_iio_buffer_postdisable(struct iio_dev *indio_dev)
+{
+	struct dht11 *dht11 = iio_priv(indio_dev);
+
+	cancel_delayed_work_sync(&dht11->work);
+	
+	return 0;
+}
+
+static const struct iio_buffer_setup_ops dht11_iio_buffer_setup_ops = {
+	.preenable = dht11_iio_buffer_preenable,
+	.postenable = dht11_iio_buffer_postenable,
+	.postdisable = dht11_iio_buffer_postdisable,
+};
+
+static int dht11_iio_buffer_init(struct iio_dev *indio_dev)
+{
+	struct iio_buffer *buffer;
+
+	buffer = iio_kfifo_allocate();
+	if (!buffer)
+		return -ENOMEM;
+
+	iio_device_attach_buffer(indio_dev, buffer);
+
+	/* Ring buffer functions - here trigger setup related */
+	indio_dev->setup_ops = &dht11_iio_buffer_setup_ops;
+
+	return 0;
+}
+
+static void dht11_work(struct work_struct *work)
+{
+	struct dht11 *dht11 = container_of(work, struct dht11, work.work);
+	struct iio_dev *iio_dev = dht11->iio;
+
+	int ret, timeres, offset;
+	uint8_t vals[2];
+
+	mutex_lock(&dht11->lock);
+	if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boot_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 = gpio_direction_output(dht11->gpio, 0);
+		if (ret) {
+			goto err;
+		}
+		usleep_range(DHT11_START_TRANSMISSION_MIN,
+				 DHT11_START_TRANSMISSION_MAX);
+		ret = gpio_direction_input(dht11->gpio);
+		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;
+		}
+	}
+
+	vals[0] = dht11->temperature;
+	vals[1] = dht11->humidity;
+	iio_push_to_buffers(iio_dev, vals);
+err:
+	dht11->num_edges = -1;
+	mutex_unlock(&dht11->lock);
+	
+	if (!ret)
+		schedule_delayed_work(&dht11->work, HZ);
+	else
+		schedule_work(&dht11->work.work);
+}
+
+static int dht11_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct device_node *node = dev->of_node;
+	struct dht11 *dht11;
+	struct iio_dev *iio;
+	int ret;
+
+	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->iio = iio;
+
+	INIT_DELAYED_WORK(&dht11->work, dht11_work);
+
+	ret = of_get_gpio(node, 0);
+	if (ret < 0)
+		return ret;
+	dht11->gpio = ret;
+	ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name);
+	if (ret)
+		return ret;
+
+	dht11->irq = gpio_to_irq(dht11->gpio);
+	if (dht11->irq < 0) {
+		dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio);
+		return -EINVAL;
+	}
+
+	dht11->timestamp = ktime_get_boot_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->dev.parent = &pdev->dev;
+	iio->info = &dht11_iio_info;
+	iio->modes = (INDIO_BUFFER_SOFTWARE | INDIO_DIRECT_MODE);
+	iio->channels = dht11_chan_spec;
+	iio->num_channels = ARRAY_SIZE(dht11_chan_spec);
+	iio->available_scan_masks = dht11_scan_masks;
+
+	dht11_iio_buffer_init(iio);
+
+	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 <harald@ccbib.org>");
+MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
+MODULE_LICENSE("GPL v2");

IMX6ULL/source/14_iio/01_dht11_iio_buffer_software/dht11.dts

@@ -0,0 +1,4 @@
+humidity_sensor {
+	compatible = "dht11";
+    gpios = <&gpio4 19 GPIO_ACTIVE_HIGH>;
+};

README.md

@@ -901,6 +901,12 @@ git clone https://e.coding.net/weidongshan/linux/doc_and_source_for_drivers.git
   01.5_通道的sysfs信息修改与体验
   ```
 
+* 2024.11.07 发布IIO"子系统"
+
+  ```shell
+  02.1_iio_buffer的核心要素与体验
+  ```
+
   
 
 ## 6. 联系方式