1Overview of IIO 2 3The Industrial I/O subsystem is intended to provide support for devices 4that in some sense are analog to digital converters (ADCs). As many 5actual devices combine some ADCs with digital to analog converters 6(DACs) that functionality is also supported. 7 8The aim is to fill the gap between the somewhat similar hwmon and 9input subsystems. Hwmon is very much directed at low sample rate 10sensors used in applications such as fan speed control and temperature 11measurement. Input is, as its name suggests focused on input 12devices. In some cases there is considerable overlap between these and 13IIO. 14 15A typical device falling into this category would be connected via SPI 16or I2C. 17 18Functionality of IIO 19 20* Basic device registration and handling. This is very similar to 21hwmon with simple polled access to device channels via sysfs. 22 23* Event chrdevs. These are similar to input in that they provide a 24route to user space for hardware triggered events. Such events include 25threshold detectors, free-fall detectors and more complex action 26detection. The events themselves are currently very simple with 27merely an event code and a timestamp. Any data associated with the 28event must be accessed via polling. 29 30Note: A given device may have one or more event channel. These events are 31turned on or off (if possible) via sysfs interfaces. 32 33* Hardware buffer support. Some recent sensors have included 34fifo / ring buffers on the sensor chip. These greatly reduce the load 35on the host CPU by buffering relatively large numbers of data samples 36based on an internal sampling clock. Examples include VTI SCA3000 37series and Analog Device ADXL345 accelerometers. Each buffer supports 38polling to establish when data is available. 39 40* Trigger and software buffer support. In many data analysis 41applications it it useful to be able to capture data based on some 42external signal (trigger). These triggers might be a data ready 43signal, a gpio line connected to some external system or an on 44processor periodic interrupt. A single trigger may initialize data 45capture or reading from a number of sensors. These triggers are 46used in IIO to fill software buffers acting in a very similar 47fashion to the hardware buffers described above. 48 49Other documentation: 50 51device.txt - elements of a typical device driver. 52 53trigger.txt - elements of a typical trigger driver. 54 55ring.txt - additional elements required for buffer support. 56 57sysfs-bus-iio - abi documentation file. 58