Abstract Comedi is a free software project to interface digital acquisition DAQ cards. The hardware of the card takes care of the sequencing and timing of the data acquisition as it proceeds. The sequence consists of a number of identically repeated scans. It is generally preferable to direct Comedi-related questions to the mailing list rather than mailing the maintainers directly. Instructions for multiple acquisitions 4.

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The mechanism part of the device interface is a faithful representation of the bare functionality of the device, independent of what part of the functionality an application will use. Buffering is another important aspect of device drivers: The API also allows you to specify the channel listi. Finding the generic similarities and structure among different cards helps in developing device drivers faster and with better documentation.

In the case of Linux as the host operating system, device driver writers must keep the following issues in mind:. DMA is a feature of the bus, not of the operating system which, of course, has to support its processes to use the feature.

A general DAQ device driver package. Kcomedilib is a Linux kernel module distributed with Comedi that provides the same interface as Comedilib in kernel space, suitable for real-time tasks.


It is the combination of three complementary software linuxx The buffer sizes are user-adjustable. The project does not provide the policy parts, such as Graphical User Interfaces to program and display acquisitions, signal processing libraries, or control algorithms.


A device driver is a piece of software that interfaces a particular piece of hardware: The drivers xomedi implemented as a core Linux kernel module providing common functionality and individual low-level driver modules.

Comedi is a free software project to interface digital acquisition DAQ cards. Your first Comedi program 3.

Integrating the driver in the Comedi library Glossary. So, the operating system provides an interface between both.

The command functionality cannot be offered by DAQ cards that lack the hardware to autonomously sequence a series of scans. Vomedi driver caveats 6.

Ubuntu Manpage: comedi – the Linux Control and Measurement Device Interface

The basic data acquisition functionalities that Comedi offers work on channels, or sets of channels:. Comedi provides the API to configure what triggering source one wants to use in each case.

Analog signals are a bit more complicated.

For example, one writes a driver for the parallel port, because one wants to use it to generate pulses that drive a stepper motor. Typically, an analog acquisition channel can be programmed to generate or read a voltage between a lower and an upper threshold e.


Comedi not only offers the API to access the functionality of the cards, but also to query the capabilities of the installed devices. For example, a set of 16 identical analog inputs.

Applications that use Comedi

This document is part of Comedilib. Abstract Comedi is a free software project to interface digital acquisition DAQ cards. Acquisition and configuration functions 4. Instructions for configuration 4. Much of Comedi has been developed by others. Introduction The Comedi project develops open-source drivers, tools, and libraries for data acquisition.

Schleef designed a structure which is a balance between modularity and complexity: Some devices also allow DMA: However, the DAQ manufacturers have never been able or willing to come up with such a standardization effort themselves.