2.  Configuration

2.1. Configuration
2.2. Getting information about a card

This section assumes that you have successfully compiled and installed the Comedi software, that your hardware device is in your computer, and that you know the relevant details about it, i.e., what kind of card it is, any jumper settings related to input ranges, the I/O base address and IRQ for old non-plug-n-play boards, etc.

2.1.  Configuration

The good news is: on most systems PCI and USB based boards are configured automatically. The kernel will detect your data acquisition devices, will load the appropriate kernel drivers and will create the /dev/comedi entries.

bp1@bp1-x61:~/sandbox/comedilib$ ls -l /dev/comedi0*
crw-rw---- 1 root iocard 98,  0 2012-04-26 23:41 /dev/comedi0
crw-rw---- 1 root iocard 98, 48 2012-04-26 23:41 /dev/comedi0_subd0
crw-rw---- 1 root iocard 98, 49 2012-04-26 23:41 /dev/comedi0_subd1

Usually these devices belong to the group iocard as shown here. The only action you need to take is to become member of this group and then the Comedi device is ready to be used.

There are a few PCI drivers that for one reason or another do not support auto-configuration, either because there is more than one variant of a board sharing the same PCI device ID (e.g. Advantech PCI-1710 and PCI-1710HG), or because some configuration options are needed (e.g. Amplicon PCI224 and PCI234) or for some other reason. It is also possible to disable auto-configuration when loading the comedi kernel module. In these cases devices need to be configured manually as for ISA cards. Conversely, most Comedi drivers supplied with the kernel sources that support auto-configuration may no longer support manual configuration.

By default, the comedi kernel module does not reserve any devices for manual configuration so manual configuration will fail. To allow devices to be configured manually, set the comedi_num_legacy_minors module parameter to the number of devices to reserve for manual configuration when loading the comedi kernel module. If using modprobe, this can be set automatically by editing /etc/modprobe.conf or /etc/modprobe.d/comedi.conf (depending on the system) to include the line:

		    options comedi comedi_num_legacy_minors=4

The number 4 in the above line may be adjusted to increase or decrease the number of devices to be reserved for manual configuration.

Old ISA based cards need to be manually configured which is explained here. You only need to read on here if you have one of these old cards. On embedded systems it might also be necessary to load the driver and then to configure the boards manually. In general manual configuration is done by running the comedi_config command (as root). Here is an example of how to use the command (perhaps you should read its man page now):

		    comedi_config /dev/comedi0 labpc-1200 0x260,3

This command says that the file /dev/comedi0 can be used to access the Comedi device that uses the labpc-1200 board, and that you give it two run-time parameters (0x260 and 3). More parameters are possible, and their meaning is driver dependant.

This tutorial goes through the process of configuring Comedi for two devices, a National Instruments AT-MIO-16E-10, and a Data Translation DT2821-F-8DI.

The NI board is plug-and-play. The current ni_atmio driver has kernel-level ISAPNP support, which is used by default if you do not specify a base address. So you could simply run comedi_config as

		    comedi_config /dev/comedi0 ni_atmio

For the preceding comedi_config command to succeed, the ni_atmio kernel module must be loaded first. For plug-n-play boards on modern kernels, the appropriate comedi kernel modules should get loaded automatically when your computer is booted. The modprobe command can be used to manually load/unload kernel modules, and lsmod will list all the currently loaded modules.

For the Data Translation board, you need to know how the board's jumpers are configured in order to specify the correct comedi_config parameters. These parameters for the board are given in the kernel drivers section about the dt282x driver. The card discussed here is a DT2821-f-8di. The entry for the dt282x driver tells you that the comedi_config parameters give the driver the I/O base, IRQ, DMA 1, DMA 2, and in addition the states of the differential/single-ended and unipolar/bipolar jumpers:

dt282x configuration options:

  • [0] - I/O port base address

  • [1] - IRQ

  • [2] - DMA 1

  • [3] - DMA 2

  • [4] - AI jumpered for 0=single ended, 1=differential

  • [5] - AI jumpered for 0=straight binary, 1=2's complement

  • [6] - AO 0 jumpered for 0=straight binary, 1=2's complement

  • [7] - AO 1 jumpered for 0=straight binary, 1=2's complement

  • [8] - AI jumpered for 0=[-10,10]V, 1=[0,10], 2=[-5,5], 3=[0,5]

  • [9] - AO 0 jumpered for 0=[-10,10]V, 1=[0,10], 2=[-5,5], 3=[0,5], 4=[-2.5,2.5]

  • [10]- A0 1 jumpered for 0=[-10,10]V, 1=[0,10], 2=[-5,5], 3=[0,5], 4=[-2.5,2.5]

So, the appropriate options list might be:


and the full configuration command is:

		    comedi_config /dev/comedi1 dt2821-f-8di 0x200,4,0,0,1,1,1,1,0,2,2

Setting the DMA channels to 0 disables the use of DMA.

So now you have your boards configured correctly. Since data acquisition boards are not typically well-engineered, Comedi sometimes can't figure out if an old non-plug-n-play board is actually in the computer and at the base address you specified. If it can't, it assumes you are right. Both of these boards are well-made, so Comedi will give an error message if it can't find them. The Comedi kernel module, since it is a part of the kernel, prints messages to the kernel logs, which you can access through the command dmesg or the file /var/log/messages. Here is a configuration failure (from dmesg):

comedi0: ni_atmio: 0x0200 can't find board

When it does work, you get:

comedi0: ni_atmio: 0x0260 at-mio-16e-10 ( irq = 3 )

Note that it also correctly identified the board.