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Installation and Configuration

2. Installation and Configuration

I assume 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, the I/O base, the IRQ, jumper settings related to input ranges, etc.

To tell the comedi kernel module that you have a particular device, and some information about it, you will be running the comedi_config command. Perhaps you should read the man page now.

In this tutorial, I will go 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, and the man page tells me that I need to configure the PnP part of the board with isapnptools. The isapnptools package is a little cryptic, but the concepts are simple. Once I learned how to use it, I settled on a /etc/isapnp.conf file that contained the lines:

# ANSI string -->National Instruments, AT-MIO-16E-10<--
(CONFIGURE NIC2400/10725401 (LD 0
	(IO 0 (BASE 0x0260))
	(INT 0 (IRQ 3 (MODE +E)))
#	(DMA 0 (CHANNEL 5))
#	(DMA 1 (CHANNEL 6))
	(ACT Y)
))

It also contains a few lines about overall configuration and about my sound card. I found out after a bit of trial-and-error that the NI board does not always work with interrupts other than IRQ 3. YMMV. Currently, the driver doesn't use DMA, but it may in the future, so I commented out the DMA lines. It is a curious fact that the device ignores the IRQ and DMA information given here, however, I keep the information here to remind myself that the numbers aren't arbitrary.

When I run comedi_config (as root, of course), I provide the same information. Since I want to have the board configured every time I boot, I put the line

/usr/sbin/comedi_config /dev/comedi0 ni_atmio 0x260,3

into /etc/rc.d/rc.local. You can, of course, run this command at a command prompt. The man page tells me that the option list is supposed to be "(I/O base),(IRQ)", so I used the same numbers as I put in /etc/isapnp.conf, i.e., 0x260,3.

For the Data Translation board, I need to have a list of the jumper settings. Fortunately, I wrote them all down in the manual -- I hope they are still correct. However, I had to open the case to figure out which board in the series I had. It is a DT2821-f-8di. The man page of comedi_config tells me that I need to know the I/O base, IRQ, DMA 1, DMA 2. However, since I wrote the driver, I know that it also recognizes the differential/single-ended and unipolar/bipolar jumpers. As always, the source is the final authority, and looking in module/dt282x.c tells me that the options list is interpreted as:

(ai=analog input, ao=analog output.) From this, I decide that the appropriate options list is

0x200,4,,1,1,1

I left the differential/single-ended number blank, since the driver already knowns (from the board name), that it is differential. I also left the DMA numbers blank, since I don't want the driver to use DMA. (Don't want it to interfere with my sound card -- life is full of difficult choices.) Keep in mind that things commented in the source, but not in the documentation are about as likely to change as the weather, so I put good comments next to the following line when I put it in rc.local.

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

So now I think that I have my boards configured correctly. Since data acquisition boards are not typically well-engineered, Comedi sometimes can't figure out if the board is actually there. If it can't, it assumes you are right. Both of these boards are well-made, so comedi will give me 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 /var/log/messages. Here is a configuration failure (from dmesg):

comedi0: ni_atmio: 0x0200 can't find board

When it does work, I get:

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

Note that it also correctly identified my board.

2.1. Getting information from comedi

So now that we have comedi talking to the hardware, we want to talk to comedi. Here's some pretty low-level information -- it's sometimes useful for debugging:

cat /proc/comedi

Right now, on my computer, this command gives:

comedi version 0.6.4
format string
 0: ni_atmio             at-mio-16e-10           7
 1: dt282x               dt2821-f-8di            4

This is a feature that is not well-developed yet. Basically, it currently tells you driver name, device name, and number of subdevices.

In the demo/ directory, there is a command called info, which provides information about each subdevice on the board. The output of it is rather long, since I have 7 subdevices (4 or fewer is common for other boards.) Here's part of the output of the NI board (which is on /dev/comedi0.) ('demo/info /dev/comedi0')

overall info:
  version code: 0x000604
  driver name: ni_atmio
  board name: at-mio-16e-10
  number of subdevices: 7
subdevice 0:
  type: 1 (unknown)
  number of channels: 16
  max data value: 4095
...

The overall info gives information about the device -- basically the same information as /proc/comedi.

This board has 7 subdevices. Devices are separated into subdevices that each have a distinct purpose -- e.g., analog input, analog output, digital input/output. This board also has an EEPROM and calibration DACs that are also subdevices.

Subdevice 0 is the analog input subdevice. You would have known this from the 'type: 1 (unknown)' line, if I've updated demo/info recently, because it would say 'type: 1 (analog input)' instead. The other lines should be self-explanitory. Comedi has more information about the device, but demo/info doesn't currently display this.