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diff --git a/drivers/staging/iio/Documentation/overview.txt b/drivers/staging/iio/Documentation/overview.txt new file mode 100644 index 000000000000..64584ad40241 --- /dev/null +++ b/drivers/staging/iio/Documentation/overview.txt @@ -0,0 +1,62 @@ +Overview of IIO + +The Industrial I/O subsytem is intended to provide support for devices +that in some sense are analog to digital convertors (ADCs). As many +actual devices combine some ADCs with digital to analog convertors +(DACs) the intention is to add that functionality at a future date +(hence the name). + +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 it's 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. They 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 ring 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 ring buffer +typically has an event chrdev (similar to the more general ones above) +to pass on events such as buffer 50% full and an access chrdev via +which the raw data it self may be read back. + +* Trigger and software ring 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 many initialize data +capture or reading from a number of sensors. These triggers are +used in iio to fill software ring buffers acting in a very similar +fashion to the hardware buffers described above. + +Other documentation: + +userspace.txt - overview of ring buffer reading from userspace + +device.txt - elemennts of a typical device driver. + +trigger.txt - elements of a typical trigger driver. + +ring.txt - additional elements required for ring buffer support + + + |