GETTING STARTED:
After installing comedi and comedilib, cd to this directory (comedilib*/demo).
Use ./board_info for a very first test. If hardware and software are correctly
installed, the program prints a list of subdevices it recognises. If the
device is not /dev/comedi0, use here and in the following the command-line
option -f <device>.
Continue with ./inp -s <subdevice> -c <channel> to read individual samples,
and with ./outp -s <subdevice> -c <channel> <integer value> to set an
output value. Other beginning demos are: cmd, dio, inpn, tut1, tut2.
You should understand how these work before trying to understand the
other demos.
The perl subdirectory contains a few examples for the perl wrapper.
DEMO PROGRAMS:
ao_waveform:
You need a device (and driver) capable of streaming analog output,
which currently is some of the members of the NI AT-MIO and PCI-MIO
E series. Creates a sine wave on an analog output channel. You
can specify the frequency of the generated sine wave on the
command line.
board_info:
Displays some information that Comedi knows about a device.
choose_clock:
Selects a master clock source. The subdevice must support
INSN_CONFIG_CLOCK_SRC. The command-line argument specifies
the clock source, and the optional -F option specifies the clock's
frequency.
choose_routing:
Changes the signal routed to a specified channel. The subdevice must support
INSN_CONFIG_SET_ROUTING. The command-line argument specifies
the signal you want routed to the specified channel. This demo
can be used, for example, to choose a what signal you want to
appear on a PFI line (which has been configured as an output)
of a National Instruments board.
common:
This is not an example. The file common.c just contains some code
that is common to many of the examples.
cmd:
An example for directly using Comedi commands. Comedi commands
are used for asynchronous acquisition, with the timing controlled
by on-board timers or external events. If this demo doesn't work
with your hardware, read the comments in the source. Hint: data
is written to stdout, comments to stderr.
dio:
Requirements: A board with a digital I/O subdevice. Not just
a 'digital input' or 'digital output' subdevice, but one in
which the channels can be configured between input and output.
Configures the specified channel as an output if passed a
nonzero argument. Otherwise, the channel is configured as
an input. Once the channel's direction has been configured,
you can read/write to it with the inp/outp demo programs.
do_waveform:
Requirements: NI M-Series board.
This demo uses the digital io subdevice with an
asynchronous command to generate waveforms. The
waveforms in this example are square waves with
varying periods depending on the digital output
channel. Channel N outputs a square wave with
period 2*(N+1) clocks. The command line argument chooses the
clock signal for updating the outputs. As a suggestion,
you might use the output of one of the general
purpose counters for a clock (the default clock
source is the output of general purpose counter 0),
and run the gpct_pulse_generator demo to start the counter
generating pulses on its output.
Note, you must configure at least one of the digital channels as
an output (for example by running the dio demo program)
before running this program. You must also pass the dio
subdevice file using the -f option, since the default write
subdevice for the m-series boards is the analog output. For
example, "dio_waveform -f /dev/comedi0_sub2".
eeprom_dump:
Dumps the EEPROM of a card, if it has one. Useful for debugging
devices/drivers.
gpct_pulse_generator:
Configures a NI general-purpose counter subdevice to produce a
continuous train of pulses on its output. The -F option specifies
the pulse period (as a frequency in Hertz), and the argument specifies
the pulse width (in nanoseconds). By default, the pulse width will
be set to half the pulse period. You may need to use the "dio"
and "choose_routing" demos to route the counter's output to
an output line that you can observe (for instance one of the PFI
lines).
gpct_simple_counting:
Configures a NI general-purpose counter subdevice to act as a
simple event counter. You can select the input to the counter
using the "choose_clock" demo. The counter's value can be read
out using the "inp" demo.
inp:
Simple input: Reads one sample from one channel on one subdevice.
inpn:
Slightly more complicated input demo. (It has a for() loop.)
Reads each channel on a subdevice, at every possible input
range, and converts the data to a voltage.
insn:
Example showing how to use instructions directly. Not
recommended for beginners: use higher-level functions such
as comedi_data_read(), comedi_data_write(), etc., as demonstrated
in the inp, outp, and dio examples.
ledclock:
This demo requires a Fantazein clock modified to be directly
controlled by the parallel port on a computer. The original
demo used a real-time task and controlled the parallel port
directly. This version is not complete.
mmap:
This example shows how to map the internal Comedi buffer
and directly access samples instead of using read() and
write(). This is very similar to cmd.c, so look there for
comments on most of the code.
outp <value>:
Write one <value> to one channel of one subdevice. Requires
a digital or analog output subdevice.
pwm:
controls PWM devices. Use the option -N 0 and -N 1 to switch
it on / off respectively. Call with no arguments to get
a help screen.
receiver:
This demo is meant to be used in conjunction with the sender
demo. Receiver requires a digital input subdevice, and sender
requires a digital output subdevice. When the clock and data
pins are connected between the sending and receiving devices,
one should be able to send bits over the link.
select:
An example for using select() with asynchronous input. This
example requires an asynchronous input subdevice that can
handle TRIG_TIMER as a scan_begin_src.
sender:
See receiver.
sigio:
Similar to the cmd demo. This demo sets up a signal handler
for SIGIO, which is called whenever data is ready to be read
from the device.
sv:
Similar to inp, but measures the input using the comedi_sv_*()
functions, which average many samples to try to get a more accurate
estimate of the actual input.
tut1:
tut2:
Tutorial examples. See the Comedilib documentation.
COMMAND-LINE OPTIONS:
Many of these demos are linked with the file common.c, which parses
command line options. Some options don't make sense with all programs.
The options are:
-a <aref> use analog reference <aref> (default: 0 == ground)
-c <chan> use channel <chan> (default: 0)
-s <subd> use subdevice <subd> (default: 0)
-r <index> use voltage range <index> (default: 0)
-f <file> use device file <file> (default: /dev/comedi0)
-n <value> use <value> for the number of channels in a scan
-N <value> use <value> for the number of scans
-F <freq> use <freq> as the scan frequency
-v verbose
-d set analog reference to differential
-g set analog reference to ground
-o set analog reference to other
-m set analog reference to common
-p display values in physical units
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