Overview of IIO The Industrial I/O subsystem is intended to provide support for devices that in some sense are analog to digital converters (ADCs). As many actual devices combine some ADCs with digital to analog converters (DACs) that functionality is also supported. The aim is to fill the gap between the somewhat similar hwmon and input subsystems. Hwmon is very much directed at low sample rate sensors used in applications such as fan speed control and temperature measurement. Input is, as its name suggests focused on input devices. In some cases there is considerable overlap between these and IIO. A typical device falling into this category would be connected via SPI or I2C. Functionality of IIO * Basic device registration and handling. This is very similar to hwmon with simple polled access to device channels via sysfs. * Event chrdevs. These are similar to input in that they provide a route to user space for hardware triggered events. Such events include threshold detectors, free-fall detectors and more complex action detection. The events themselves are currently very simple with merely an event code and a timestamp. Any data associated with the event must be accessed via polling. Note: A given device may have one or more event channel. These events are turned on or off (if possible) via sysfs interfaces. * Hardware buffer support. Some recent sensors have included fifo / ring buffers on the sensor chip. These greatly reduce the load on the host CPU by buffering relatively large numbers of data samples based on an internal sampling clock. Examples include VTI SCA3000 series and Analog Device ADXL345 accelerometers. Each buffer supports polling to establish when data is available. * Trigger and software buffer support. In many data analysis applications it it useful to be able to capture data based on some external signal (trigger). These triggers might be a data ready signal, a gpio line connected to some external system or an on processor periodic interrupt. A single trigger may initialize data capture or reading from a number of sensors. These triggers are used in IIO to fill software buffers acting in a very similar fashion to the hardware buffers described above. Other documentation: device.txt - elements of a typical device driver. trigger.txt - elements of a typical trigger driver. ring.txt - additional elements required for buffer support. sysfs-bus-iio - abi documentation file.