For these cards, the command functionality may be provided in software. For example, a analog output card can be used to generate voltages that are the inputs for the electronic drivers of 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. Normal application programs can run their processes only in user space, 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. 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. Features Integrated real-time support for most hardware High-level library comedilib Application-level device independence Requires a Linux 2. Typically, an analog acquisition channel can be programmed to generate or read a voltage between a lower and an upper threshold e. Other cards have the hardware to do two or more acquisitions in parallel, and can perform all the conversions in a scan simultaneously.
|Date Added:||9 August 2016|
|File Size:||21.12 Mb|
|Operating Systems:||Windows NT/2000/XP/2003/2003/7/8/10 MacOS 10/X|
|Price:||Free* [*Free Regsitration Required]|
Callbacks, events and interrupts 6. Other cards have the hardware to do two or more acquisitions in parallel, and can perform all the conversions in a scan simultaneously. Functions for comeddi acquisition 4. Comedi not only offers the API to access the functionality of the cards, but also to query the capabilities of the installed devices.
Commands for streaming acquisition 4. For example, a analog output card can be used to generate voltages that are the inputs for the electronic drivers of the motors of a robot; these voltages can be interpreted as setpoints for the desired velocity comfdi these motors, and six of them are taken together to steer one particular robot with six-degrees of freedom.
Applications that use Comedi
So, the hardware puts a lower boundary the scan interval on the minimum time needed to complete a full scan. And because of the quite strict real-time requirements for a command acquisition, a real-time operating system should be used to translate the command specification into a correctly timed sequence of instructions. Only privileged processes can run in the kernel, where they have access to all hardware and to all kernel data structures. Normal users program against the API of the Comedilib user-space library.
The precise timing between the acquisitions is not hardware controlled. The API also allows you to specify the channel listi. The sequence consists of a number of identically repeated scans.
One golden rule for the device driver writer is to separate mechanism and policy:. DMA is a feature of the bus, not of the operating system which, of course, has to support its processes to use the feature. Users who write an application for a particular device, must link their application to that device’s device driver.
Linxu type of cards are often called data acquisition or DAQ cards. So, the function call blocks until the whole acquisition has finished.
Each scan contains one or more conversions on particular channels, i.
For example, one writes a driver for the parallel port, because one wants to use it to generate pulses that drive a stepper motor. 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:. The basic data acquisition functionalities that Comedi offers work on channels, or sets of channels:.
Abstract Comedi is a free software project to interface digital acquisition DAQ cards.
Comedi – Control and Measurement Interface
It translates the primitive, device-dependent commands with which the hardware manufacturer allows you to configure, read and write the electronics of the hardware interface into more abstract and generic function calls and data structures for the application programmer. Your first Comedi program 3. Comedi is a collection of drivers for a variety of common data acquisition plug-in boards.
The drivers are implemented as a core Linux kernel module providing common functionality and individual low-level driver modules.
This section gives a high-level introduction to which functionality you can expect from the software. In addition, some hardware has limits on the minimum conversion interval it can achieve, i. 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.
Applications that use Comedi
Device drivers are often written by application programmers, that have only their particular application in mind; especially in real-time applications. Digital signals are conceptually quite simple, and don’t need much configuration: Almost all devices can be interfaced in PIO mode: Writing Comedi programs 3.
In the context of this document, the term “source code” as defined by the license is interpreted as the XML source. Acquisition and configuration functions 4.