1. 什么是 IIO 子系统？
1.1 IIO 概述
1.2 IIO 相关的组件
2. IIO 功能特性
3. IIO 相关配置
3.1 配置内核
3.2 配置设备树
3.2.1 IIO providers
3.2.2 IIO consumers
4. IIO API
4.1 用户空间 API
4.1.1 4种接口
4.1.2 操作实例
5. 更多值得学习的知识点
6. 相关参考
ADC / DAC
加速度计
磁力计
陀螺仪
压力传感器
湿度传感器
温度传感器
...
类似于 input 子系统，iio 子系统也可以向应用层上报事件(hardware triggered events)，例如阈值检测事件，自由落体检测事件、更复杂的动作检测事件;
目前 event 的格式为：event code + 时间戳;
$ make menuconfig
Device Drivers --->
<*> Industrial I/O support --->
[*] Enable buffer support within IIO
< > IIO callback buffer used for push in-kernel interfaces
<*> Industrial I/O HW buffering
<*> Industrial I/O buffering based on kfifo
< > Enable IIO configuration via configfs
[*] Enable triggered sampling support
(2) Maximum number of consumers per trigger
< > Enable software triggers support
Accelerometers --->
Analog to digital converters --->
Amplifiers --->
Chemical Sensors --->
Hid Sensor IIO Common ----
SSP Sensor Common --->
Digital to analog converters --->
IIO dummy driver --->
Frequency Synthesizers DDS/PLL --->
Digital gyroscope sensors --->
Health Sensors --->
Humidity sensors --->
Inertial measurement units --->
Light sensors --->
Magnetometer sensors --->
Inclinometer sensors ----
Triggers - standalone --->
Digital potentiometers --->
Pressure sensors --->
Lightning sensors --->
Proximity sensors --->
Temperature sensors --->
io-channel-cells，０ 表示只有 1 路 IIO output，１ 表示有多路 IIO output;
io-channel-ranges: 一个 empty 属性(即不用赋值)，会在 driver/iio/inkern.c/iio_channel_get() 中被引用，它表明继承了当前节点的子节点可以引用当前节点的 IIO channel;
adc: voltage-sensor@ 35 {
compatible = "maxim,max1139";
reg = < 0x35>;
#io-channel-cells = <1>;
};
adc@ 35 {
compatible = "some-vendor,some-adc";
reg = < 0x35>;
adc1: iio-device@ 0 {
#io-channel-cells = <1>;
/* other properties */
};
adc2: iio-device@ 1 {
#io-channel-cells = <1>;
/* other properties */
};
};
IIO consumer 节点的形式是 <phandle iio_specifier>;
它的作用是连接 IIO provider 的 input 端到 IIO consumer 的 output 端;
其中，phandle 是 IIO provider 的句柄，specifier 用于选择第几路 channel;
类似 gpio specifier， IIO specifier 是有 １ 个或者多个 cells 的数组，用于确定 IIO device的 output 端，即 １ 个 cell 对应一个 IIO channel output;
IIO specifier 数组的长度由 IIO provider 节点的 #io-channel-cells 属性决定;
some_consumer {
io-channels = <&adc 1>, <&ref 0>;
io-channel-names = "vcc", "vdd";
};
/sys/bus/iio/devices/iio:deviceX;
可用于配置 /dev/iio:deviceX 接口的 events / data
可用于轮循的方式低速地直接读/写 IIO 设备;
Documentation/ABI/testing/sysfs-bus-iio;
/dev/iio:deviceX，该接口在 IIO 子系统里是可选非必要的;
标准的文件 IO API: open(), read(), write(), close().
用于读取 events 和 data;
用于配置额外的 IIO 特性，例如：软件 triggers 或者 hrtimer triggers;
详细说明：
$ grep -H "" /sys/bus/iio/devices /*/name | grep adc
/sys/bus/iio/devices/iio:device0/name:48003000.adc:adc@0
/sys/bus/iio/devices/iio:device1/name:48003000.adc:adc@1
$ cd /sys/bus/iio/devices/iio:device0/
$ cat in_voltage6_raw # Convert ADC1 channel 0 (analog-to-digital): get raw value
40603
$ cat in_voltage_scale # Read scale
0.044250488
$ cat in_voltage_offset # Read offset
0
$ awk "BEGIN{printf (\"%d\n\", (40603 + 0) * 0.044250488)}"
1796
$ lsiio | grep dac
Device 003: 40017000.dac:dac@ 1
Device 004: 40017000.dac:dac@ 2
$ cd /sys/bus/iio/devices/iio:device3/
$ cat out_voltage1_scale # Read scale
0.708007812
$ awk "BEGIN{printf (\"%d\n\", 2000 / 0.708007812)}" # 假设要输出 2000 mV
2824
$ echo 2824 > out_voltage1_raw # Write raw value to DAC1
$ echo 0 > out_voltage1_powerdown # Enable DAC1 (out of power-down mode)
本文授权转载自公众号“嵌入式Hacker”，作者吴伟东Jack
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