十七、IIO子系统(一)

17.1 简介

IIO是支持模数转换/数模转换，即ADC/DAC以及多种传感器的Linux子系统。

以下是IIO子系统支持的传感器：
******* ADC——模-数转换器
******* DAC——数模转换器
******* CDC——电容-数字转换器
******* 加速度计
******* 陀螺仪
******* IMU——惯性测量仪
******* 颜色和光传感器
******* 磁力计
******* 压力传感器
******* 距离传感器
******* 温度传感器

关于Linux工业I/O子系统详细位于Linux驱动实现API指南，如下：

https://www.kernel.org/doc/html/latest/driver-api/iio/core.html

IIO核心提供如下功能：
为各类嵌入式传感器驱动程序编写提供统一框架；
为操作传感器的用户太应用程序提供标准接口，如下；

IIO框架提供几种接口，如下：
******* 1、/sys/bus/iio/iio:deviceX  代表一个硬件传感器，按照通道呈现；
******* 2、/dev/iio:deviceX 代表字符设备节点，用于输出事件和传感器数据，可以使用open()、read()、write()、close()函数来访问；

iio内存申请函数使用，如下：

devm_iio_device_alloc()

将设备注册到内核，如下：

devm_iio_device_register()

IIO设备的sysfs接口

在 /sys/bus/iio/iio:deviceX/目录下，部分属性如下：
******* name 是对物理芯片的描述
******* dev 是节点对应的主/从设备号
******* 设备配置属性
******* 数据通道访问属性，如out_voltage0_raw

17.2 数模转换——DAC实验

iio属性定义来自，如下：

driver/iio/industrialio-core.c

17.2.1 IIO缓冲区

IIO缓冲区的使用可以降低CPU消耗。

17.2.2 触发器

驱动程序大多情况下，是基于外部事件（触发器）来捕获数据，。而不是周期性的轮询数据。该驱动能有一个产生硬件事件的设备，也可以有一个具备独立终端源，如接收到外部GPIO线、定时器中断或者用户态特定sysfs文件的写操作的驱动来提供。

17.2.3 工业I/O事件

 展示到用户态的sysfs事件属性，几乎所有的IIO事件都是对应着从传感器督导一个或多个原始数据阈值，例如：
******* 越过电压阈值；
******* 均值超过阈值；
******* 运动检测器；
******* 平方和均方根的阈值；
******* 变化率阈值；

向用户态传递IIO事件

include<linux/iio/events.h>iio_push_event()

17.2.4 iio工具

位于/tools/iio/目录，如下：
******* lsiio
******* iio_event_monitor
******* iio_generic_buffer
******* libiio

17.2.5 LTC2607——DAC模块介绍

内核模块将会操作Analog Device 公司的LTC2607设备。双路12bit、100kHZ和400KHZ 电压输出的DAC，使用I2C串行接口。

该驱动包括三部分，如下：
******* 设备树
******* 操作I2C交互的工业框架
******* IIO设备工业框架

17.2.5.1 设备树

			i2c2: i2c@600 {compatible = "atmel,sama5d2-i2c";reg = <0x600 0x200>;interrupts = <20 IRQ_TYPE_LEVEL_HIGH 7>;dmas = <0>, <0>;dma-names = "tx", "rx";#address-cells = <1>;#size-cells = <0>;clocks = <&flx1_clk>;pinctrl-names = "default";pinctrl-0 = <&pinctrl_mikrobus_i2c>;atmel,fifo-size = <16>;status = "okay";ltc2607@72 {compatible = "arrow,ltc2607";reg = <0x72>;   #I2C设备地址};ltc2607@73 {compatible = "arrow,ltc2607";reg = <0x73>;   #I2C设备地址};};

17.2.5.2 LTC2607驱动模块介绍

17.2.5.2.1 用作I2C交互的工业框架

必须包含的头文件，如下：

#include <linux/i2c.h>
通过包含该头文件，可以引用 struct i2c_driver、 struct i2c_client()、i2c_get_clientdata()、i2c_set_clientdata()

创建有一个i2c_driver数据结构，如下：

static struct i2c_driver ltc2607_driver = {.driver = {.name	= LTC2607_DRV_NAME,.owner	= THIS_MODULE,.of_match_table = dac_dt_ids,},.probe		= ltc2607_probe,.remove		= ltc2607_remove,.id_table	= ltc2607_id,
};

作为i2c驱动注册到I2C总线，如下：

module_i2c_driver(ltc2607_driver);

添加到驱动支持的设备列表，如下：

static const struct of_device_id dac_dt_ids[] = {{ .compatible = "arrow,ltc2607", },{ }
};
MODULE_DEVICE_TABLE(of, dac_dt_ids);

定义i2c_device_id类型数组，如下：

static const struct i2c_device_id ltc2607_id[] = {{ "ltc2607", 0 },{ }
};
MODULE_DEVICE_TABLE(i2c, ltc2607_id);

17.2.5.2.2 用作IIO设备的工业框架

包含的头文件，如下：

#include <linux/iio/iio.h>
通过引用上面头文件，可以使用 iio_priv、devm_iio_device_alloc()

LTC2607驱动力的物理和逻辑设备数据结构之间关联，如下：

static const struct iio_info ltc2607_info = {.write_raw = ltc2607_write_raw,.driver_module = THIS_MODULE,
};ltc2607_write_raw()函数，调用 ltc2607_set_value()函数再调用，i2c_master_send()函数。

计算公式：
DAC值的范围是0 ~ 0xFFFF(65535)
输出电压 = Vref * DAC值 / 65535
Vref = 5V

17.2.5.3 源代码

#include <linux/module.h>
#include <linux/i2c.h>
#include <linux/iio/iio.h>#define LTC2607_DRV_NAME "ltc2607"struct ltc2607_device {struct i2c_client *client;char name[8];
};static const struct iio_chan_spec ltc2607_channel[] = {
{.type		= IIO_VOLTAGE,.indexed	= 1,.output		= 1,.channel	= 0,.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
},{.type		= IIO_VOLTAGE,.indexed	= 1,.output		= 1,.channel	= 1,.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
},{.type		= IIO_VOLTAGE,.indexed	= 1,.output		= 1,.channel	= 2,.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
}};static int ltc2607_set_value(struct iio_dev *indio_dev, int val, int channel)
{struct ltc2607_device *data = iio_priv(indio_dev);u8 outbuf[3];int ret;int chan;if (channel == 2)chan = 0x0F;elsechan = channel;if (val >= (1 << 16) || val < 0)return -EINVAL;outbuf[0] = 0x30 | chan; /* write and update DAC */outbuf[1] = (val >> 8) & 0xff; /* MSB byte of dac_code */outbuf[2] = val & 0xff; /* LSB byte of dac_code */ret = i2c_master_send(data->client, outbuf, 3);if (ret < 0)return ret;else if (ret != 3)return -EIO;elsereturn 0;
}static int ltc2607_write_raw(struct iio_dev *indio_dev,struct iio_chan_spec const *chan,int val, int val2, long mask)
{int ret;switch (mask) {case IIO_CHAN_INFO_RAW:ret = ltc2607_set_value(indio_dev, val, chan->channel);return ret;default:return -EINVAL;}
}static const struct iio_info ltc2607_info = {.write_raw = ltc2607_write_raw,.driver_module = THIS_MODULE,
};static int ltc2607_probe(struct i2c_client *client,const struct i2c_device_id *id)
{static int counter = 0;struct iio_dev *indio_dev;struct ltc2607_device *data;u8 inbuf[3];u8 command_byte;int err;dev_info(&client->dev, "DAC_probe()\n");command_byte = 0x30 | 0x00; /* Write and update register with value 0xFF*/inbuf[0] = command_byte;inbuf[1] = 0xFF;inbuf[2] = 0xFF;/* allocate the iio_dev structure */indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));if (indio_dev == NULL) return -ENOMEM;data = iio_priv(indio_dev);	i2c_set_clientdata(client, data);data->client = client;sprintf(data->name, "DAC%02d", counter++);dev_info(&client->dev, "data_probe is entered on %s\n", data->name);indio_dev->name = data->name;indio_dev->dev.parent = &client->dev;indio_dev->info = &ltc2607_info;indio_dev->channels = ltc2607_channel;indio_dev->num_channels = 3;indio_dev->modes = INDIO_DIRECT_MODE;err = i2c_master_send(client, inbuf, 3); /* write DAC value */if (err < 0) {dev_err(&client->dev, "failed to write DAC value");return err;}dev_info(&client->dev, "the dac answer is: %x.\n", err);err = devm_iio_device_register(&client->dev, indio_dev);if (err)return err;dev_info(&client->dev, "ltc2607 DAC registered\n");return 0;
}static int ltc2607_remove(struct i2c_client *client)
{dev_info(&client->dev, "DAC_remove()\n");return 0;
}static const struct of_device_id dac_dt_ids[] = {{ .compatible = "arrow,ltc2607", },{ }
};
MODULE_DEVICE_TABLE(of, dac_dt_ids);static const struct i2c_device_id ltc2607_id[] = {{ "ltc2607", 0 },{ }
};
MODULE_DEVICE_TABLE(i2c, ltc2607_id);static struct i2c_driver ltc2607_driver = {.driver = {.name	= LTC2607_DRV_NAME,.owner	= THIS_MODULE,.of_match_table = dac_dt_ids,},.probe		= ltc2607_probe,.remove		= ltc2607_remove,.id_table	= ltc2607_id,
};
module_i2c_driver(ltc2607_driver);MODULE_AUTHOR(" ");
MODULE_DESCRIPTION("LTC2607 16-bit DAC");
MODULE_LICENSE("GPL");

17.3 模数转换——ADC实验

首先，介绍开发一个不具有硬件触发功能的ADC，该ADC——SPI设备LTC2422. LTC2422是20bit 双通道ADC，即模拟——数字转换芯片，LTC串行输出数据流，如下：

LTC2422输出数据流长度是24bit.
******* 片选引脚——CS
******* 数据线——SDO  即MISO管脚
******* 串行时钟——SCK

在driver/spi/spidev.c是通用SPI设备驱动，可以通过内核配置来启动它，即 CONFIG_SPI_SPIDEV.

17.3.1 ADC模块设备树

				spi3: spi@400 {compatible = "atmel,at91rm9200-spi";reg = <0x400 0x200>;interrupts = <23 IRQ_TYPE_LEVEL_HIGH 7>;clocks = <&flx4_clk>;clock-names = "spi_clk";#address-cells = <1>;#size-cells = <0>;pinctrl-names = "default";pinctrl-0 = <&pinctrl_mikrobus_spi &pinctrl_mikrobus1_spi_cs &pinctrl_mikrobus2_spi_cs>;atmel,fifo-size = <16>;status = "okay"; /* Conflict with uart6 and i2c3. */spidev@0 {compatible = "spidev";spi-max-frequency = <2000000>;reg = <0>;};ADC: ltc2422@0 {compatible = "arrow,ltc2422";spi-max-frequency = <2000000>;reg = <0>;  #片选信号CS值pinctrl-0 = <&pinctrl_key_gpio_default>;int-gpios = <&pioA PIN_PA29 GPIO_ACTIVE_LOW>;interrupt-parent = <&pioA>;interrupts = <29  IRQ_TYPE_EDGE_FALLING>;};};

17.3.2 ADC模块用作spi交互的工业框架分析

包含头文件，如下：

#include <linux/spi/spi.h>

定义spi_driver数据结构，如下：

static struct spi_driver ltc2422_driver = {.driver = {.name	= "ltc2422",.owner	= THIS_MODULE,.of_match_table = ltc2422_dt_ids,},.probe		= ltc2422_probe,.id_table	= ltc2422_id,
};

将其作为驱动注册到SPI总线上，如下：

module_spi_driver(ltc2422_driver);

定义一个spi_device_id数据结构数组，如下：

static const struct spi_device_id ltc2422_id[] = {{ .name = "ltc2422", },{ }
};
MODULE_DEVICE_TABLE(spi, ltc2422_id);

17.3.3 ADC模块用作iio设备的工业框架分析

包含头文件，如下：

#include <linux/iio/iio.h>
用于devm_iio_alloc()、iio_priv()

创建用于管理设备的私有数据结构，如下：

struct ltc2422_state {struct spi_device *spi;u8 buffer[4];
};

将设备注册到IIO核心里，如下：

devm_iio_device_register(&spi->dev, indio_dev);

一个IIO设备代表一个数据通道，一个IIO设备可以有一个或多个数据通道。添加iio:device生成多个通道，如下：

static const struct iio_chan_spec ltc2422_channel[] = {{.type		= IIO_VOLTAGE,.indexed	= 1,.output		= 1,.channel	= 0,.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
}};

给iio_info数据结构赋值，用户态对sysfs数据通道属性的操作都会被映射到内核的回调函数上，如下：

static const struct iio_info ltc2422_info = {.read_raw = &ltc2422_read_raw,.driver_module = THIS_MODULE,
};

ltc2422_read_raw()函数调用spi_read()函数，如下：

static int ltc2422_read_raw(struct iio_dev *indio_dev,struct iio_chan_spec const *chan, int *val, int *val2, long m)
{int ret;struct ltc2422_state *st = iio_priv(indio_dev);switch (m) {case IIO_CHAN_INFO_RAW:ret = spi_read(st->spi, &st->buffer, 3);if (ret < 0)return ret;*val  = st->buffer[0] << 16;*val |= st->buffer[1] << 8;*val |= st->buffer[2];dev_info(&st->spi->dev, "the value is %x\n", *val);return IIO_VAL_INT;default:return -EINVAL;}
}

17.3.4 ADC模块源代码

#include <linux/module.h>
#include <linux/spi/spi.h>
#include <linux/iio/iio.h>struct ltc2422_state {struct spi_device *spi;u8 buffer[4];
};static const struct iio_chan_spec ltc2422_channel[] = {{.type		= IIO_VOLTAGE,.indexed	= 1,.output		= 1,.channel	= 0,.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
}};static int ltc2422_read_raw(struct iio_dev *indio_dev,struct iio_chan_spec const *chan, int *val, int *val2, long m)
{int ret;struct ltc2422_state *st = iio_priv(indio_dev);switch (m) {case IIO_CHAN_INFO_RAW:ret = spi_read(st->spi, &st->buffer, 3);if (ret < 0)return ret;*val  = st->buffer[0] << 16;*val |= st->buffer[1] << 8;*val |= st->buffer[2];dev_info(&st->spi->dev, "the value is %x\n", *val);return IIO_VAL_INT;default:return -EINVAL;}
}static const struct iio_info ltc2422_info = {.read_raw = &ltc2422_read_raw,.driver_module = THIS_MODULE,
};static int ltc2422_probe(struct spi_device *spi)
{struct iio_dev *indio_dev;struct ltc2422_state *st;int err;dev_info(&spi->dev, "my_probe() function is called.\n");const struct spi_device_id *id = spi_get_device_id(spi);indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*st));if (indio_dev == NULL)return -ENOMEM;st = iio_priv(indio_dev);st->spi = spi;indio_dev->dev.parent = &spi->dev;indio_dev->channels = ltc2422_channel;indio_dev->info = &ltc2422_info;indio_dev->name = id->name;indio_dev->num_channels = 1;indio_dev->modes = INDIO_DIRECT_MODE;err = devm_iio_device_register(&spi->dev, indio_dev);if (err < 0)return err;return 0;
}static const struct of_device_id ltc2422_dt_ids[] = {{ .compatible = "arrow,ltc2422", },{ }
};MODULE_DEVICE_TABLE(of, ltc2422_dt_ids);static const struct spi_device_id ltc2422_id[] = {{ .name = "ltc2422", },{ }
};
MODULE_DEVICE_TABLE(spi, ltc2422_id);static struct spi_driver ltc2422_driver = {.driver = {.name	= "ltc2422",.owner	= THIS_MODULE,.of_match_table = ltc2422_dt_ids,},.probe		= ltc2422_probe,.id_table	= ltc2422_id,
};
module_spi_driver(ltc2422_driver);MODULE_AUTHOR(" ");
MODULE_DESCRIPTION("LTC2422 DUAL ADC");
MODULE_LICENSE("GPL");

17.3.5 应用代码

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/types.h>int8_t read_adc();/* The LTC2422 least significant bit value with 5V full-scale */
float LTC2422_lsb = 4.7683761E-6;  /* The LTC2422 least significant bit value with 3.3V full-scale */
/* float LTC2422_lsb = 3.1471252E-6; *//* check which number is the ADC iio:deviceX and replace x by the number */
#define LTC2422_FILE_VOLTAGE	"/sys/bus/iio/devices/iio:device2/out_voltage0_raw"
#define SPI_DATA_CHANNEL_OFFSET 22
#define SPI_DATA_CHANNEL_MASK   (1 << SPI_DATA_CHANNEL_OFFSET)
#define LTC2422_CONVERSION_TIME     137 /* ms *//* * Returns the Data and Channel Number(0- channel 0, 1-Channel 1)* Returns the status of the SPI read. 0=successful, 1=unsuccessful.*/
int8_t LTC2422_read(uint8_t *adc_channel, int32_t *code);/* Returns the Calculated Voltage from the ADC Code */
float LTC2422_voltage(uint32_t adc_code, float LTC2422_lsb);int8_t LTC2422_read(uint8_t *adc_channel, int32_t *code)
{int a2dReading = 0;FILE *f = fopen(LTC2422_FILE_VOLTAGE, "r");int read = fscanf(f, "%d", &a2dReading);if (read <= 0) {printf("ERROR: Unable to read values from voltage input file.\n");exit(-1);}/* Determine the channel number */*adc_channel = (a2dReading & SPI_DATA_CHANNEL_MASK) ? 1 : 0;*code = a2dReading;fclose(f);return(0);
}/* Returns the Calculated Voltage from the ADC Code */
float LTC2422_voltage(uint32_t adc_code, float LTC2422_lsb)
{float adc_voltage;if (adc_code & 0x200000){adc_code &= 0xFFFFF; /* Clears Bits 20-23 */adc_voltage=((float)adc_code)*LTC2422_lsb;}else{adc_code &= 0xFFFFF; /* Clears Bits 20-23 */adc_voltage = -1*((float)adc_code)*LTC2422_lsb;}return(adc_voltage);
}void delay(unsigned int ms)
{usleep(ms*1000);
}int8_t read_adc()
{float adc_voltage;int32_t adc_code;uint8_t adc_channel;int32_t  adc_code_array;           int8_t return_code;int a2dReading = 0;LTC2422_read(&adc_channel, &adc_code);delay(LTC2422_CONVERSION_TIME);LTC2422_read(&adc_channel, &adc_code);adc_voltage = LTC2422_voltage(adc_code, LTC2422_lsb);printf("the value of ADC channel %d\n", adc_channel);printf("     is : %6.4f\n", adc_voltage);delay(LTC2422_CONVERSION_TIME);LTC2422_read(&adc_channel, &adc_code);adc_voltage = LTC2422_voltage(adc_code, LTC2422_lsb);printf("the value of ADC channel %d\n", adc_channel);printf("     is : %6.4f\n", adc_voltage);return(0);
}int main(void)
{read_adc();printf("Application termined\n");return 0;
}

17.3.6 ADC调试

insmod  ltc2422_daul_device.ko
cd /sys/bus/iio/devices
cat out_voltage0_raw
echo 65535 > out_voltage0_rawrmmod  ltc2422_daul_device.ko

感谢阅读，祝君成功！
-by aiziyou