Specifications

Comedi

6 / 148

• [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:

0x200,4,0,0,1,1,1,1,0,2,2

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.

2.2 Getting information about a card

So now that you have Comedi talking to the hardware, try to talk to Comedi. Call the command comedi_board_info, which

provides information about each subdevice on the board. Here’s part of the output for the USB-DUX sigma board (which is on

/dev/comedi0), as a result of the command comedi_board_info -v.

overall info:

version code: 0x00074c

driver name: usbduxsigma

board name: usbduxsigma

number of subdevices: 4

subdevice 0:

type: 1 (analog input)

flags: 0x10119000

SDF_CMD_READ:can do asynchronous input commands

SDF_READABLE:subdevice can be read

SDF_GROUND:can do aref=ground

SDF_LSAMPL:subdevice uses 32-bit samples for commands

number of channels: 16

max data value: 16777215