Communication user-space — kernel-space 6. For these cards, the command functionality may be provided in software. A general DAQ device driver package 1. It is the combination of three complementary software items: It is effectively a “kernel library” for using Comedi from real-time tasks. Device drivers typically must access specific addresses on the bus, and hence must at least partially run in kernel space. Commands for streaming acquisition 4.
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Normal application programs can run their processes only in user comedii, where these processes are shielded from each other, and from direct access to hardware and to critical data of the operating system; these user space programs execute much of the operating system’s functionality through system calls.
So, the operating system provides an interface between both.
It is generally preferable to direct Comedi-related questions to the mailing list rather than mailing the maintainers directly. Included in the Comedilib package are documentation, configuration and calibration utilities, and demonstration programs.
This is where the actual data acquisitions are taking place: Features Integrated real-time support for most hardware High-level library comedilib Application-level device independence Vomedi a Linux 2.
Schleef designed a structure which is a balance between modularity and complexity: Comedi not only offers the API to access the functionality of the cards, but also to query the capabilities of the installed devices.
Comedi is ilnux collection of drivers for a variety of common data acquisition plug-in boards.
Applications that use Comedi
The hardware of the card takes care of the sequencing and timing of the data acquisition as it proceeds. Getting information about a card 3. Finding the generic similarities and structure among different cards helps in developing device drivers faster and with better documentation. Fomedi all devices can be interfaced in PIO mode: Constants and macros 5. For example, one writes a driver for the parallel port, because one wants to use it to generate pulses that drive a stepper motor.
The source code is distributed in two main packages, comedi and comedilib:. The sequence consists of a kinux of identically repeated scans. Comedi is a free software project to interface digital acquisition DAQ cards. Abstract Comedi is a free software project to interface digital comdi DAQ cards.
Instruction for internal triggering 4. This approach often leads to device drivers that depend too much on that particular application, and are not general enough to be re-used for other applications. The comedu are implemented as a core Linux kernel module providing common functionality and individual low-level driver modules.
The command functionality cannot be offered by DAQ cards that lack the hardware to autonomously co,edi a series of scans. Device drivers are often written by application programmers, that have only their particular application in mind; especially in real-time applications. From the point of view of application developers, there are many reasons to welcome the standardization of the API and the architectural structure of DAQ software:.
Your first Comedi program 3. The API also allows you to specify the channel listi. DMA is a feature of the bus, not of the operating system which, of course, xomedi to support its processes to use the feature.
Comedi – Control and Measurement Interface
Writing Comedi programs 3. Comedi has still only a limited number of drivers for this kind of signals, although most of the necessary API and support functionality is available. The cards supported in Comedi have one or more of the following signals: Typically, an analog acquisition channel can be programmed to generate or read a voltage between a lower and an upper threshold e. Your second Comedi program 3. A general DAQ device driver package 1.
Hardware Supported by Comedi
For example, a analog output card can be used to generate voltages that are the inputs for the electronic drivers fomedi the motors of a robot; these voltages can be interpreted as setpoints for the desired velocity of these motors, and six of them are taken together to steer one particular robot with six-degrees of freedom.
So, Comedi focuses only on the mechanism part of DAQ interfacing. Some devices also allow DMA: