int main(int argc,char *argv[])
{
comedi_t *it;
- int chan=0;
lsampl_t data;
it=comedi_open("/dev/comedi0");
- comedi_data_read(it,subdev,chan,range,aref,& data);
+ comedi_data_read(it,subdev,chan,range,aref,&data);
printf("%d\n",data);
</verb></tscreen>
-Should be understandable. Open the device, get the data,
+Should be understandable: open the device, get the data,
print it out. This is basically the guts of <tt>demo/inp.c</tt>,
without error checking or fancy options.
Compile it using
<sect1>Converting samples to voltages
<p>
-If you selected an analog input subdevice, you should notice
+If you selected an analog input subdevice, you probably noticed
that the output of <tt>tut1</tt> is a number between
0 and 4095, or 0 and 65535, depending on the number of bits
in the A/D converter. Comedi samples are <bf>always</bf> unsigned,
input, and Comedi allows you to select which of these to
use. This parameter is called the "range parameter", since
it specifies the "input range" for analog input (or "output range"
-analog output.) The range parameter represents both the gain
+for analog output.) The range parameter represents both the gain
and the unipolar/bipolar aspects.
Comedi keeps the number of available ranges and the largest
<tscreen><verb>
#include <stdio.h> /* for printf() */
#include <comedi.h> /* also included by comedilib.h */
-#include <comedilib.h> /* for comedi_get() */
+#include <comedilib.h> /* 'cuz we're using comedilib */
int subdev = 0; /* change this to your input subdevice */
int chan = 0; /* change this to your channel */
{
comedi_t *cf;
int chan=0;
- int data;
+ lsampl_t data;
int maxdata,rangetype;
double volts;
rangetype=comedi_get_rangetype(cf,subdev,chan);
- data=comedi_get(cf->fd,subdev,chan,range,aref);
+ comedi_data_read(cf->fd,subdev,chan,range,aref,&data);
volts=comedi_to_phys(data,rangetype,range,maxdata);
</verb></tscreen>
-By now, the <tt>comedi_read_data()</tt> line looks a little archaic, using
-the UNIX file descriptor cf->fd instead of just cf. (By the
-way, somewhere in the heart of <tt>comedi_open()</tt> is the line
-<tt>cf->fd=open(filename,O_RDWR)</tt>.) Well, there isn't one good
-replacement, since it highly depends on your application
-what additional features you might want in a <tt>comedi_get()</tt>
-replacement. But this is the topic of a different section.
-
-
<p>
<sect>Application-specific functions
<p>
<ref id="comedi_cmd" name="comedi_cmd"> structure. The source types are:
<itemize>
-<item>TRIG_NONE: don't ever cause an event, sometimes used as a stop_src.
-<item>TRIG_NOW: cause event to occur immediately, the most common start_src.
-It is also used sometimes as a convert_src for 'burst mode' aquisition where
-the individual channels in a scan are scanned through as quickly as possible.
-<item>TRIG_FOLLOW: see notes below, usually used as a scan_begin_src.
+<item>TRIG_NONE: don't ever cause an event
+<item>TRIG_NOW: cause event to occur immediately
+<item>TRIG_FOLLOW: see notes below
<item>TRIG_TIME: cause event to occur at a particular time
-<item>TRIG_TIMER: cause event to occur repeatedly at a specific rate, often
-used as a scan_begin_src or convert_src.
-<item>TRIG_COUNT: cause event when count reaches specific value, almost always
-used as the scan_end_src and often for stop_src.
-<item>TRIG_EXT: external signal causes event, used as start_src for externally
-triggered conversions, and as scan_begin_src or convert_src for externally paced
-conversions.
-<item>TRIG_INT: internal signal causes event, will probably be used as start_src
-for output commands in the future.
+<item>TRIG_TIMER: cause event to occur repeatedly at a specific rate
+<item>TRIG_COUNT: cause event when count reaches specific value
+<item>TRIG_EXT: external signal causes event
+<item>TRIG_INT: internal signal causes event
+<item>TRIG_OTHER: driver-specific meaning
</itemize>
For every trigger, there is a corresponding
structure) whose meaning depends on the type of trigger. The meanings
of the arguments are as follows:
-<itemize>
-<item>trigger src = TRIG_NONE: argument has no meaning
-<item>trigger src = TRIG_NOW: argument is the delay in nanoseconds before triggering
-<item>trigger src = TRIG_FOLLOW: argument has no meaning
-<item>trigger src = TRIG_TIME: argument is the time at which to trigger (in what units??),
-but no drivers support this yet.
-<item>trigger src = TRIG_TIMER: argument is the period in nanoseconds between triggers
-<item>trigger src = TRIG_COUNT: argument is the number of 'counts' per trigger.
-For comedi_cmd.stop_arg, this is the number of scans to perform before ending aquisition.
-For comedi_cmd.scan_end_arg, this is the number of conversions to perform per scan.
-<item>trigger src = TRIG_EXT: argument is the digital input channel to trigger on.
-<item>trigger src = TRIG_INT: argument meaning is unknown??
-</itemize>
Not all triggers are applicable to all events. Supported triggers
for specific events depends significantly on your particular
device.
-TRIG_FOLLOW is a special type of trigger for scan_begin events that
-triggers on the next lower level trigger, in this case, the trigger
-for convert events. It may or may not be supported. Later, it may
-also be used for start events if you want to chain multiple commands.
+TRIG_NONE is typically used only as a stop_src. The arg for TRIG_NONE
+is reserved and should be set to 0.
+
+TRIG_NOW is most often used as a start_src. The arg for TRIG_NOW is
+the number of nanoseconds between when the command is issued and when
+the event should occur. In the case of using TRIG now as a start_src,
+it indicates a delay between issuing the command and the start of
+acquisition. Most drivers only support a delay of 0.
+
+TRIG_FOLLOW is a special type of trigger for events that trigger on
+the completion of some other, logically connected event. The argument
+is reserved and should be set to 0. When used
+as a scan_begin_src, it indicates that a trigger should occur as a
+logical continuation of convert events. This is done in order to
+properly describe boards that do not have separate timers for
+convert and scan_begin events. When used as a start_src for analog
+output subdevices, it indicates that conversion of output samples
+should begin when samples are written to the buffer.
+
+TRIG_TIME is reserved for future use.
+
+TRIG_TIMER is most often used as a convert_src, a scan_begin_src, or
+both. It indicates that triggers should occur at a specific rate.
+The argument specifies the interval between triggers in nanoseconds.
+
+TRIG_COUNT is used for scan_end_src and stop_src. It indicates that
+a trigger should occur when the specified number of corresponding
+lower-level triggers (convert and scan_begin, respectively) occur.
+The argument is the count of lower-level triggers.
+
+TRIG_EXT can be useful as any of the trigger sources. It indicates
+that an external digital line should be used to trigger the event.
+The exact meaning of digital line is device-dependent. Some devices
+have one dedicated line, others may allow generic digital input
+lines to be used. The argument indicates the particular external
+line to use as the trigger.
+
+TRIG_INT is typically used as a start_src. This trigger occurs when
+the application performs an INSN_INTTRIG instruction. Using TRIG_INT
+is a method by which the application can accurately record the time of
+the start of acquisition, since the parsing and setup time of a
+particular command may be significant. The argument associated with
+TRIG_INT is reserved and should be set to 0.
+
+TRIG_OTHER can be useful as any of the trigger sources. The exact
+meaning of TRIG_OTHER is driver-specific, and implements a feature
+that otherwise does not fit into the command interface. Configuration
+of TRIG_OTHER features are done by INSN_CONFIG insns. The argument
+is reserved and should be set to 0.
+
The chanlist member of the <ref id="comedi_cmd" name="comedi_cmd">
structure should point to an array whose number of elements is specificed by chanlist_len
projects / comedilib.git / commitdiff