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4 <!ENTITY % comedilib_entities SYSTEM "comedilib.ent">
8 <section id="acquisitionfunctions">
10 Acquisition and configuration functions
14 This Section gives an overview of all &comedi; functions with which
15 application programmers can implement their data acquisition. (With
16 <quote>acquisition</quote> we mean all possible kinds of interfacing
17 with the cards: input, output, configuration, streaming, etc.)
18 <xref linkend="comedireference"/> explains the function calls in full
22 <section id="singleacquisition">
24 Functions for single acquisition
28 The simplest form of using &comedi; is to get one single sample to or
29 from an interface card. This sections explains how to do such simple
30 <link linkend="dio">digital</link> and
31 <link linkend="singleanalog">analog</link> acquisitions.
36 Single digital acquisition
40 Many boards supported by &comedi; have digital input and output
41 channels; i.e., channels that can only produce a <literal>0</literal>
42 or a <literal>1</literal>.
43 Some boards allow the <emphasis>direction</emphasis> (input or output)
44 of each channel to be specified independently in software.
48 &comedi; groups digital channels into a
49 <emphasis>subdevice</emphasis>, which is a group of digital channels
50 that have the same characteristics. For example, digital output lines
51 will be grouped into a digital
52 output subdevice, bidirectional digital lines will be grouped
53 into a digital I/O subdevice. Thus, there can be multiple
54 digital subdevices on a particular board.
58 Individual bits on a digital I/O device can be read and written using
59 the functions <function><link linkend="func-ref-comedi-dio-read">comedi_dio_read</link></function>
60 and <function><link linkend="func-ref-comedi-dio-write">comedi_dio_write</link></function>:
62 <funcsynopsis><funcprototype>
63 <funcdef>int <function>comedi_dio_read</function></funcdef>
64 <paramdef>comedi_t *<parameter>device</parameter></paramdef>
65 <paramdef>unsigned int <parameter>subdevice</parameter></paramdef>
66 <paramdef>unsigned int <parameter>channel</parameter></paramdef>
67 <paramdef>unsigned int *<parameter>bit</parameter></paramdef>
68 </funcprototype></funcsynopsis>
70 <funcsynopsis><funcprototype>
71 <funcdef>int <function>comedi_dio_write</function></funcdef>
72 <paramdef>comedi_t *<parameter>device</parameter></paramdef>
73 <paramdef>unsigned int <parameter>subdevice</parameter></paramdef>
74 <paramdef>unsigned int <parameter>channel</parameter></paramdef>
75 <paramdef>unsigned int <parameter>bit</parameter></paramdef>
76 </funcprototype></funcsynopsis>
78 The <parameter class="function">device</parameter> parameter is a
79 <link linkend="ref-type-comedi-t">pointer</link>
80 to a successfully opened &comedi; device.
81 The <parameter class="function">subdevice</parameter> and
82 <parameter class="function">channel</parameter> parameters are positive
83 integers that indicate which subdevice and channel is used in the
84 acquisition. The integer <parameter class="function">bit</parameter>
85 contains the value of the acquired bit.
88 The direction of bidirectional lines can be configured using the function
89 <function><link linkend="func-ref-comedi-dio-config">comedi_dio_config</link></function>:
91 <funcsynopsis><funcprototype>
92 <funcdef>int <function>comedi_dio_config</function></funcdef>
93 <paramdef>comedi_t *<parameter>device</parameter></paramdef>
94 <paramdef>unsigned int <parameter>subdevice</parameter></paramdef>
95 <paramdef>unsigned int <parameter>channel</parameter></paramdef>
96 <paramdef>unsigned int <parameter>dir</parameter></paramdef>
97 </funcprototype></funcsynopsis>
99 The parameter <parameter class="function">dir</parameter> should be
100 either <constant>COMEDI_INPUT</constant> or
101 <constant>COMEDI_OUTPUT</constant>.
102 Many digital I/O subdevices group channels into blocks for
103 configuring direction. Changing one channel in a block changes
108 Multiple channels can be read and written simultaneously using the
109 function <function><link linkend="func-ref-comedi-dio-bitfield2">comedi_dio_bitfield2</link></function>:
111 <funcsynopsis><funcprototype>
112 <funcdef>int <function>comedi_dio_bitfield2</function></funcdef>
113 <paramdef>comedi_t *<parameter>device</parameter></paramdef>
114 <paramdef>unsigned int <parameter>subdevice</parameter></paramdef>
115 <paramdef>unsigned int <parameter>write_mask</parameter></paramdef>
116 <paramdef>unsigned int *<parameter>bits</parameter></paramdef>
117 <paramdef>unsigned int <parameter>base_channel</parameter></paramdef>
118 </funcprototype></funcsynopsis>
120 Each channel from <parameter class="function">base_channel</parameter>
121 to <parameter class="function">base_channel</parameter> +
122 <literal>31</literal> is assigned to a bit in the
123 <parameter class="function">write_mask</parameter> and
124 <parameter class="function">bits</parameter>
125 bitfield with bit 0 assigned to channel
126 <parameter class="function">base_channel</parameter>, bit 1 assigned to channel
127 <parameter class="function">base_channel</parameter> +
128 <literal>1</literal>, etc. If a bit in
129 <parameter class="function">write_mask</parameter> is set, the
130 corresponding bit in <parameter class="function">*bits</parameter> will
131 be written to the digital output line corresponding to the channel given by
132 <parameter class="function">base_channel</parameter> plus the bit number.
133 Each digital line is then read and placed into
134 <parameter class="function">*bits</parameter>. The value
135 of bits in <parameter class="function">*bits</parameter> corresponding
136 to digital output lines is undefined and device-specific. Channel
137 <parameter class="function">base_channel</parameter> +
138 <literal>0</literal> is the least significant bit in the bitfield. No
139 more than 32 channels at once can be accessed using this method.
140 <emphasis role="strong">Warning!</emphasis> Older versions of &comedi;
141 may ignore <parameter class="function">base_channel</parameter> and treat
142 it as <literal>0</literal> unless the subdevice has more than 32 channels.
146 The digital acquisition functions seem to be very simple, but, behind
147 the implementation screens of the &comedi; kernel module, they are
148 executed as special cases of the general
149 <link linkend="instructions">instruction</link> command.
156 <section id="singleanalog">
158 Single analog acquisition
161 Analog &comedi; channels can produce data values that are
162 <emphasis>samples</emphasis> from continuous analog signals.
163 These samples are integers with a significant content in
164 the range of, typically, 8, 10, 12, or 16 bits.
167 Single samples can be read from an analog channel using the function
168 <function><link linkend="func-ref-comedi-data-read">comedi_data_read</link></function>:
170 <funcsynopsis><funcprototype>
171 <funcdef>int <function>comedi_data_read</function></funcdef>
172 <paramdef>comedi_t *<parameter>device</parameter></paramdef>
173 <paramdef>unsigned int <parameter>subdevice</parameter></paramdef>
174 <paramdef>unsigned int <parameter>channel</parameter></paramdef>
175 <paramdef>unsigned int <parameter>range</parameter></paramdef>
176 <paramdef>unsigned int <parameter>aref</parameter></paramdef>
177 <paramdef>lsampl_t *<parameter>data</parameter></paramdef>
178 </funcprototype></funcsynopsis>
180 This reads one such data value from a &comedi; channel, and puts it in
181 the user-specified <parameter class="function">data</parameter> buffer.
185 The <parameter class="function">range</parameter> parameter is the zero-based
186 index of one of the gain ranges supported by the channel. This is a number
187 from 0 to N-1 where N is the number of ranges supported by the channel.
189 <function><link linkend="func-ref-comedi-get-n-ranges">comedi_get_n_ranges</link></function>
190 to get the number of ranges supported by the channel, the function
191 <function><link linkend="func-ref-comedi-find-range">comedi_find_range</link></function>
192 to search for a suitable range, or the function
193 <function><link linkend="func-ref-comedi-get-range">comedi_get_range</link></function>
194 to get the details of a supported range.
198 The <parameter class="function">aref</parameter> parameter specifies an
199 analog reference to use:
200 <constant><link linkend="aref-ground">AREF_GROUND</link></constant>,
201 <constant><link linkend="aref-common">AREF_COMMON</link></constant>,
202 <constant><link linkend="aref-diff">AREF_DIFF</link></constant>, or
203 <constant><link linkend="aref-other">AREF_OTHER</link></constant>.
205 <function><link linkend="func-ref-comedi-get-subdevice-flags">comedi_get_subdevice_flags</link></function>
206 to see which analog references are supported by the subdevice.
210 In the opposite direction, single samples can be written to an analog output
211 channel using the function
212 <function><link linkend="func-ref-comedi-data-write">comedi_data_write</link></function>:
214 <funcsynopsis><funcprototype>
215 <funcdef>int <function>comedi_data_write</function></funcdef>
216 <paramdef>comedi_t *<parameter>device</parameter></paramdef>
217 <paramdef>unsigned int <parameter>subdevice</parameter></paramdef>
218 <paramdef>unsigned int <parameter>channel</parameter></paramdef>
219 <paramdef>unsigned int <parameter>range</parameter></paramdef>
220 <paramdef>unsigned int <parameter>aref</parameter></paramdef>
221 <paramdef>lsampl_t <parameter>data</parameter></paramdef>
222 </funcprototype></funcsynopsis>
226 Raw data values read or written by the above functions
227 are unsigned integers less than, or equal to, the maximum sample value
228 of the channel, which can be determined using the function
229 <function><link linkend="func-ref-comedi-get-maxdata">comedi_get_maxdata</link></function>:
231 <funcsynopsis><funcprototype>
232 <funcdef>lsampl_t <function>comedi_get_maxdata</function></funcdef>
233 <paramdef>comedi_t *<parameter>device</parameter></paramdef>
234 <paramdef>unsigned int <parameter>subdevice</parameter></paramdef>
235 <paramdef>unsigned int <parameter>channel</parameter></paramdef>
236 </funcprototype></funcsynopsis>
238 Conversion between raw data values and uncalibrated physical units can
239 be performed by the functions
240 <function><link linkend="func-ref-comedi-to-phys">comedi_to_phys</link></function>
241 and <function><link linkend="func-ref-comedi-from-phys">comedi_from_phys</link></function>:
243 <funcsynopsis><funcprototype>
244 <funcdef>double <function>comedi_to_phys</function></funcdef>
245 <paramdef>lsampl_t <parameter>data</parameter></paramdef>
246 <paramdef>comedi_range *<parameter>range</parameter></paramdef>
247 <paramdef>lsampl_t <parameter>maxdata</parameter></paramdef>
248 </funcprototype></funcsynopsis>
250 <funcsynopsis><funcprototype>
251 <funcdef>lsampl_t <function>comedi_from_phys</function></funcdef>
252 <paramdef>double <parameter>data</parameter></paramdef>
253 <paramdef>comedi_range *<parameter>range</parameter></paramdef>
254 <paramdef>lsampl_t <parameter>maxdata</parameter></paramdef>
255 </funcprototype></funcsynopsis>
259 There are some data structures in these commands that are not fully
265 <type><link linkend="ref-type-comedi-t">comedi_t</link></type>: this data structure
266 contains all information that a user program has to know about an
267 <emphasis>open</emphasis> &comedi; device. The programmer doesn't have
268 to fill in this data structure manually: it gets filled in by opening
275 <type><link linkend="ref-type-lsampl-t">lsampl_t</link></type>: this
276 <quote>data structure</quote> represents one single sample. On most
277 architectures, it's nothing more than a 32 bits value. Internally,
278 &comedi; does some conversion from raw sample data to
279 <quote>correct</quote> integers. This is called <quote>data
286 <type><link linkend="ref-type-comedi-range">comedi_range</link></type>:
287 this holds the minimum and maximum physical values for a gain range supported
288 by a channel of a subdevice, and specifies the units. This can be used in
289 combination with the channel's <quote>maxdata</quote> value to convert between
290 unsigned integer sample values (of type
291 <type><link linkend="ref-type-lsampl-t">lsampl_t</link></type> or
292 <type><link linkend="ref-type-sampl-t">sampl_t</link></type>) and physical
293 units in a nominal (uncalibrated) way using the
294 <function><link linkend="func-ref-comedi-to-phys">comedi_to_phys</link></function>
296 <function><link linkend="func-ref-comedi-from-phys">comedi_from_phys</link></function>
298 <function><link linkend="func-ref-comedi-get-maxdata">comedi_get_maxdata</link></function>
299 function to get the <quote>maxdata</quote> value for the channel.
302 Most functions specify the range to be used for a channel by a zero-based
303 index into the list of ranges supported by the channel. Depending on the
304 device and subdevice, different channels on the subdevice may or may not
305 share the same list of ranges, that is, ranges may or may not be
306 channel-specific. (The <constant>SDF_RANGETYPE</constant> subdevice flag
307 indicates whether ranges are channel-specific.)
314 Each single acquisition by, for example,
315 <function><link linkend="func-ref-comedi-data-read">comedi_data_read</link></function>
316 requires quite some overhead, because all the arguments of the
317 function call are checked. If multiple acquisitions must be done on
318 the same channel, this overhead can be avoided by using a function
319 that can read more than one sample,
320 <function><link linkend="func-ref-comedi-data-read-n">comedi_data_read_n</link></function>:
322 <funcsynopsis><funcprototype>
323 <funcdef>int <function>comedi_data_read_n</function></funcdef>
324 <paramdef>comedi_t *<parameter>device</parameter></paramdef>
325 <paramdef>unsigned int <parameter>subdevice</parameter></paramdef>
326 <paramdef>unsigned int <parameter>channel</parameter></paramdef>
327 <paramdef>unsigned int <parameter>range</parameter></paramdef>
328 <paramdef>unsigned int <parameter>aref</parameter></paramdef>
329 <paramdef>lsampl_t *<parameter>data</parameter></paramdef>
330 <paramdef>unsigned int <parameter>n</parameter></paramdef>
331 </funcprototype></funcsynopsis>
333 The number of samples, <parameter class="function">n</parameter>, is
334 limited by the &comedi; implementation (to a maximum of 100 samples),
335 because the call is blocking.
338 The start of the a single data acquisition can also be delayed by a specified
339 number of nano-seconds using the function
340 <function><link linkend="func-ref-comedi-data-read-delayed">comedi_data_read_delayed</link></function>:
342 <funcsynopsis><funcprototype>
343 <funcdef>int <function>comedi_data_read_delayed</function></funcdef>
344 <paramdef>comedi_t *<parameter>device</parameter></paramdef>
345 <paramdef>unsigned int <parameter>subdevice</parameter></paramdef>
346 <paramdef>unsigned int <parameter>channel</parameter></paramdef>
347 <paramdef>unsigned int <parameter>range</parameter></paramdef>
348 <paramdef>unsigned int <parameter>aref</parameter></paramdef>
349 <paramdef>lsampl_t *<parameter>data</parameter></paramdef>
350 <paramdef>unsigned int <parameter>nano_sec</parameter></paramdef>
351 </funcprototype></funcsynopsis>
355 All these read and write acquisition functions are implemented on top
356 of the generic <link linkend="instructions">instruction</link>
365 <section id="instructions">
367 Instructions for multiple acquisitions
370 The <emphasis>instruction</emphasis> is one of the most generic,
371 overloaden and flexible functions in the &comedi; API. It is used to
372 execute a multiple of identical acquisitions on the same channel, but
374 <link linkend="instructionsconfiguration">configuration</link> of a
376 <anchor id="anchor.instruction.list"/>
377 An <emphasis>instruction list</emphasis> is a list of instructions,
378 possibly on different channels. Both instructions and instructions
379 lists are executed <emphasis>synchronously</emphasis>, i.e., while
380 <emphasis role="strong">blocking</emphasis> the calling process.
381 This is one of the limitations of instructions; the other one is that
382 they cannot code an acquisition involving timers or external events.
383 These limits are eliminated by the
384 <link linkend="commandsstreaming">command</link> acquisition
389 <section id="comediinsnstructure">
391 The instruction data structure
394 All the information needed to execute an instruction is stored in the
395 <type><link linkend="ref-type-comedi-insn">comedi_insn</link></type>
398 typedef struct <anchor id="insn-data-structure"/>comedi_insn_struct {
399 <anchor id="insn-data-structure-insn"/>unsigned int insn; // integer encoding the type of acquisition
400 // (or configuration)
401 unsigned int n; // number of elements in data array
402 <link linkend="ref-type-lsampl-t">lsampl_t</link> <anchor id="insn-data-structure-data"/>*data; // pointer to data buffer
403 unsigned int subdev; // subdevice
404 unsigned int <anchor id="insn-data-structure-chanspec"/><link linkend="ref-macro-CR-PACK">chanspec</link>; // encoded channel specification
405 unsigned int unused[3];
408 Because of the large flexibility of the instruction function, many
409 types of instruction do not need to fill in all fields, or attach
410 different meanings to the same field. But the current implementation
411 of &comedi; requires the
412 <structfield><link linkend="insn-data-structure-data">data</link></structfield>
413 field to be at least one byte long.
417 The <structfield><link linkend="insn-data-structure-insn">insn</link></structfield> member of the
418 <link linkend="insn-data-structure">instruction data structure</link>
419 determines the type of acquisition executed in the corresponding
425 <constant>INSN_READ</constant>: the instruction executes a read on an
432 <constant>INSN_WRITE</constant>: the instruction executes a write on an
439 <constant>INSN_BITS</constant>: indicates that the instruction must
440 read or write values on multiple digital I/O channels.
446 <constant>INSN_GTOD</constant>: the instruction performs a
447 <quote>Get Time Of Day</quote> acquisition.
453 <constant>INSN_WAIT</constant>: the instruction blocks for a specified
454 number of nanoseconds.
464 <section id="instructionexecution">
466 Instruction execution
469 Once an instruction data structure has been filled in, the
470 corresponding instruction is executed with the function
471 <function><link linkend="func-ref-comedi-do-insn">comedi_do_insn</link></function>:
473 <funcsynopsis><funcprototype>
474 <funcdef>int <function>comedi_do_insn</function></funcdef>
475 <paramdef>comedi_t *<parameter>device</parameter></paramdef>
476 <paramdef>comedi_insn *<parameter>instruction</parameter></paramdef>
477 </funcprototype></funcsynopsis>
479 Many &comedi; instructions are shortcuts that relieve the programmer
480 from explicitly filling in the data structure and calling the
481 <function><link linkend="func-ref-comedi-do-insn">comedi_do_insn</link></function>
485 A list of instructions can be executed in one function call using the function
486 <function><link linkend="func-ref-comedi-do-insnlist">comedi_do_insnlist</link></function>:
488 <funcsynopsis><funcprototype>
489 <funcdef>int <function>comedi_do_insnlist</function></funcdef>
490 <paramdef>comedi_t *<parameter>device</parameter></paramdef>
491 <paramdef>comedi_insnlist *<parameter>list</parameter></paramdef>
492 </funcprototype></funcsynopsis>
494 The parameter <parameter class="function">list</parameter> is a pointer to a
495 <type><link linkend="insnlist-data-structure">comedi_insnlist</link></type>
496 data structure holding a pointer to an array of <type>comedi_insn</type>
497 and the number of instructions in the list:
499 typedef struct <anchor id="insnlist-data-structure"/>comedi_insnlist_struct {
500 unsigned int n_insns;
506 The number of instructions in the list is limited in the
507 implementation, because instructions are executed
508 <emphasis>synchronously</emphasis>, i.e., the call blocks until the
509 whole instruction (list) has finished.
517 <section id="instructionsconfiguration">
519 Instructions for configuration
522 <xref linkend="instructions"/> explains how instructions are used to do
523 <emphasis>acquisition</emphasis> on channels. This section explains
524 how they are used to <emphasis>configure</emphasis> a subdevice.
525 There are various sorts of configurations, and the
526 specific information for each different configuration possibility is
527 to be specified via the
528 <structfield><link linkend="insn-data-structure-data">data</link></structfield>
530 <link linkend="insn-data-structure">instruction data structure</link>.
531 (So, the pointer to a
532 <type><link linkend="ref-type-lsampl-t">lsampl_t</link></type>
533 is misused as a pointer to an array with board-specific information.)
537 Using <constant>INSN_CONFIG</constant> as the
538 <structfield><link linkend="insn-data-structure-insn">insn</link></structfield>
540 <link linkend="insn-data-structure">instruction data structure</link>
541 indicates that the instruction will
542 <emphasis>not perform acquisition</emphasis> on a
543 channel, but will <emphasis>configure</emphasis> that channel.
545 <structfield><link linkend="ref-macro-CR-PACK">chanspec</link></structfield>
547 <type><link linkend="insn-data-structure-chanspec">comedi_insn</link></type>
548 data structure, contains the channel to be configured.
549 The zeroth element of the data array
550 is always an id that specifies
551 what type of configuration instruction is being performed. The
552 meaning of rest of the elements in the data array
553 depend on the configuration instruction id.
555 possible ids are summarised in the table below, along with the
556 meanings of the data array elements for
557 each type of configuration instruction.
561 <tgroup cols='4' align='left'>
562 <colspec colwidth='4*' />
563 <colspec colwidth='4*' />
564 <colspec colwidth='1*' />
565 <colspec colwidth='4*' />
568 <entry>data[0]</entry>
569 <entry>Description</entry>
570 <entry>n (number of elements in data array)</entry>
571 <entry>Meanings of data[1], ..., data[n-1]</entry>
576 <entry><constant>INSN_CONFIG_DIO_INPUT</constant></entry>
578 Configure a DIO line as input. It is easier to use
579 <function><link linkend="func-ref-comedi-dio-config">comedi_dio_config</link></function>
580 than to use this configuration instruction directly.
588 <entry><constant>INSN_CONFIG_DIO_OUTPUT</constant></entry>
590 Configure a DIO line as output. It is easier to use
591 <function><link linkend="func-ref-comedi-dio-config">comedi_dio_config</link></function>
592 than to use this configuration instruction directly.
600 <entry><constant>INSN_CONFIG_ALT_SOURCE</constant></entry>
602 Select an alternate input source. This instruction is used by calibration
603 programs to configure analog input channels
604 which can be redirected to read internal calibration
605 references. You need to set the <constant>CR_ALT_SOURCE</constant> flag in the chanspec
606 when reading to actually read from the configured alternate input source.
607 If you are using <function>comedi_data_read</function>, then the channel parameter can be
608 bitwise or'd with the <constant>CR_ALT_SOURCE</constant> flag.
612 data[1]: alternate input source.
616 <entry><constant>INSN_CONFIG_BLOCK_SIZE</constant></entry>
618 Specify block size for asynchonous command data.
619 When performing streaming input, many boards accumulate
620 samples in internal fifos and transfer them to the host
621 computer in chunks. Some drivers let you suggest a size in bytes for how big a
622 the chunks should be. This lets you tune how often the host computer is
623 interrupted with a new chunk of data.
627 data[1]: The desired block size in bytes. The actual configured block size is
628 writen back to data[1] after the instruction completes. This instruction
629 acts purely as a query if the block size is set to zero.
633 <entry><constant>INSN_CONFIG_DIO_QUERY</constant></entry>
635 Queries the configuration of a DIO line to see if it is an input or output.
636 It is probably easier to use the comedilib function
637 <function><link linkend="func-ref-comedi-dio-get-config">comedi_dio_get_config</link></function>
638 than to use this instruction directly.
642 data[1]: The instruction sets this element to either
643 <constant>COMEDI_INPUT</constant> or <constant>COMEDI_OUTPUT</constant>.
651 See the comedilib demo program <filename>demo/choose_clock.c</filename> for an example
652 of using a configuration instruction.
658 <section id="inttrigconfiguration">
660 Instruction for internal triggering
663 This special instruction has
664 <anchor id="insn-inttrig"/><constant>INSN_INTTRIG</constant> as the
665 <structfield><link linkend="insn-data-structure-insn">insn</link></structfield>
667 <link linkend="insn-data-structure">instruction data structure</link>.
668 Its execution causes an
669 <link linkend="trig-int-start-src">internal triggering event</link>. This
670 event can, for example, cause the device driver to start a conversion,
671 or to stop an ongoing acquisition. The exact meaning of the triggering
672 depends on the card and its particular driver.
676 <structfield><link linkend="insn-data-structure-data">data</link></structfield>[0] element of the
677 <constant>INSN_INTTRIG</constant> instruction is reserved for future use,
678 and should be set to <literal>0</literal>.
684 <section id="commandsstreaming">
686 Commands for streaming acquisition
690 The most powerful &comedi; acquisition primitive is the
691 <emphasis>command</emphasis>. It's powerful because, with one single
692 command, the programmer launches:
697 a possibly infinite <emphasis>sequence of acquisitions</emphasis>,
703 accompanied with various <emphasis>callback</emphasis> functionalities
704 (DMA, interrupts, driver-specific callback functions),
710 for <emphasis>any number of channels</emphasis>,
716 with an <emphasis>arbitrary order</emphasis> of channels in each scan
717 (possibly even with repeated channels per scan),
723 and with various scan <emphasis>triggering sources</emphasis>,
724 external (i.e., hardware pulses) as well as internal (i.e., pulses
725 generated on the DAQ card itself, or generated by a
726 <link linkend="inttrigconfiguration">software trigger instruction</link>).
731 This command functionality exists in the &comedi; API, because various
732 data acquisition devices have the capability to perform this kind of
733 complex acquisition, driven by either on-board or
734 off-board timers and triggers.
738 A command specifies a particular data
739 <link linkend="fig-acq-seq">acquisition sequence</link>, which
740 consists of a number of <emphasis>scans</emphasis>, and each scan is
741 comprised of a number of <emphasis>conversions</emphasis>, which
742 usually corresponds to a single A/D or D/A conversion. So, for
743 example, a scan could consist of sampling channels 1, 2 and 3 of a
744 particular device, and this scan should be repeated 1000 times, at
745 intervals of 1 millisecond apart.
748 The command function is complementary to the
749 <link linkend="instructionsconfiguration">configuration instruction</link>
750 function: each channel in the command's
751 <structfield><link linkend="command-data-struct-chanlist">chanlist</link></structfield>
752 should first be configured by an appropriate instruction.
756 <section id="executingcommand">
762 A command is executed by the function
763 <function><link linkend="func-ref-comedi-command">comedi_command</link></function>:
765 <funcsynopsis><funcprototype>
766 <funcdef>int <function>comedi_command</function></funcdef>
767 <paramdef>comedi_t *<parameter>device</parameter></paramdef>
768 <paramdef>comedi_cmd *<parameter>command</parameter></paramdef>
769 </funcprototype></funcsynopsis>
771 The following sections explain the meaning of the
772 <type><link linkend="ref-type-comedi-cmd">comedi_cmd</link></type> data structure.
773 Filling in this structure can be quite complicated, and
774 requires good knowledge about the exact functionalities of the DAQ
775 card. So, before launching a command, the application programmer is
776 adviced to check whether this complex command data structure can be
777 successfully parsed. So, the typical sequence for executing a command is
778 to first send the command through
779 <function><link linkend="func-ref-comedi-command-test">comedi_command_test</link></function>
780 once or twice. The test will check that the command is valid for the
781 particular device, and often makes some adjustments to the command
782 arguments, which can then be read back by the user to see the actual
786 A &comedi; program can find out on-line what the command capabilities
787 of a specific device are, by means of the
788 <function><link linkend="func-ref-comedi-get-cmd-src-mask">comedi_get_cmd_src_mask</link></function>
795 <section id="comedicmdstructure">
797 The command data structure
800 The command executes according to the information about the requested
801 acquisition, which is stored in the
802 <type><link linkend="ref-type-comedi-cmd">comedi_cmd</link></type>
803 <anchor id="command-data-struct"/>data structure:
805 typedef struct comedi_cmd_struct comedi_cmd;
807 struct comedi_cmd_struct {
808 unsigned int subdev; // which subdevice to sample
809 unsigned int <anchor id="command-data-struct-flags"/>flags; // encode some configuration possibilities
810 // of the command execution; e.g.,
811 // whether a callback routine is to be
812 // called at the end of the command
814 unsigned int <anchor id="command-data-struct-start-src"/>start_src; // event to make the acquisition start
815 unsigned int <anchor id="command-data-struct-start-arg"/>start_arg; // parameters that influence this start
817 unsigned int <anchor id="command-data-struct-scan-begin-src"/>scan_begin_src; // event to make a particular scan start
818 unsigned int <anchor id="command-data-struct-scan-begin-arg"/>scan_begin_arg; // parameters that influence this start`
820 unsigned int <anchor id="command-data-struct-convert-src"/>convert_src; // event to make a particular conversion start
821 unsigned int <anchor id="command-data-struct-convert-arg"/>convert_arg; // parameters that influence this start
823 unsigned int <anchor id="command-data-struct-scan-end-src"/>scan_end_src; // event to make a particular scan terminate
824 unsigned int <anchor id="command-data-struct-scan-end-arg"/>scan_end_arg; // parameters that influence this termination
826 unsigned int <anchor id="command-data-struct-stop-src"/>stop_src; // what make the acquisition terminate
827 unsigned int <anchor id="command-data-struct-stop-arg"/>stop_arg; // parameters that influence this termination
829 unsigned int <anchor id="command-data-struct-chanlist"/>*chanlist; // pointer to list of channels to be sampled
830 unsigned int <anchor id="command-data-struct-chanlist-len"/>chanlist_len; // number of channels to be sampled
832 sampl_t *<anchor id="command-data-struct-data"/>data; // address of buffer
833 unsigned int <anchor id="command-data-struct-data-len"/>data_len; // number of samples to acquire
836 The start and end of the whole command acquisition sequence, and the
837 start and end of each scan and of each conversion, is triggered by a
838 so-called <emphasis>event</emphasis>. More on these in
839 <xref linkend="comedicmdsources"/>.
843 The <parameter class="function">subdev</parameter> member of the
844 <type><link linkend="ref-type-comedi-cmd">comedi_cmd</link></type> structure is
845 the index of the subdevice the command is intended for. The
846 <function><link linkend="func-ref-comedi-find-subdevice-by-type">comedi_find_subdevice_by_type</link></function>
847 function can be useful in discovering the index of your desired subdevice.
851 The <structfield><link linkend="command-data-struct-chanlist">chanlist</link></structfield>
853 <type><link linkend="ref-type-comedi-cmd">comedi_cmd</link></type> data
854 structure should point to an array whose number of elements is
856 <structfield><link linkend="command-data-struct-chanlist-len">chanlist_len</link></structfield>
857 (this will generally be the same as the
858 <structfield><link linkend="command-data-struct-scan-end-arg">scan_end_arg</link></structfield>).
860 <structfield><link linkend="command-data-struct-chanlist">chanlist</link></structfield>
861 specifies the sequence of channels and gains (and analog references)
862 that should be stepped through for each scan. The elements of the
863 <structfield><link linkend="command-data-struct-chanlist">chanlist</link></structfield> array should be
864 initialized by <quote>packing</quote> the channel, range and reference
865 information together with the
866 <function><link linkend="ref-macro-CR-PACK">CR_PACK</link></function>
871 The <structfield><link linkend="command-data-struct-data">data</link></structfield> and
872 <structfield><link linkend="command-data-struct-data-len">data_len</link></structfield>
873 members can be safely ignored when issueing commands from a user-space
874 program. They only have meaning when a command is sent from a
875 <emphasis role="strong">kernel</emphasis> module using the
876 <systemitem>kcomedilib</systemitem> interface, in which case they specify
877 the buffer where the driver should write/read its data to/from.
881 The final member of the
882 <type><link linkend="command-data-struct">comedi_cmd</link></type> structure is the
883 <structfield><link linkend="command-data-struct-flags">flags</link></structfield> field,
884 i.e., bits in a word that can be bitwise-or'd together. The meaning of
885 these bits are explained in
886 <xref linkend="comedicmdflags"/>.
892 <section id="comedicmdsources">
894 The command trigger events
895 <anchor id="source.trigger.anchor"/>
898 A command is a very versatile acquisition instruction, in the sense
899 that it offers lots of possibilities to let different hardware and
900 software sources determine when acquisitions are started, performed,
901 and stopped. More specifically, the command
902 <link linkend="command-data-struct">data structure</link>
903 has <emphasis>five</emphasis> types of events: start the
904 <link linkend="acquisitionterminology">acquisition</link>,
905 start a <link linkend="scan">scan</link>, start a
906 <link linkend="conversion">conversion</link>, stop a scan, and stop
907 the acquisition. Each event can be given its own
908 <emphasis><link linkend="source.trigger.anchor">source</link></emphasis>
909 (the <parameter class="function">…_src</parameter> members in the
910 <type><link linkend="ref-type-comedi-cmd">comedi_cmd</link></type> data
911 structure). And each event source can have a corresponding
912 argument (the <parameter class="function">…_arg</parameter> members of
913 the <type><link linkend="ref-type-comedi-cmd">comedi_cmd</link></type> data
914 structure) whose meaning depends on the type of source trigger.
915 For example, to specify an external digital line <quote>3</quote> as a
916 source (in general, <emphasis>any</emphasis> of the five event
917 sources), you would use
918 <parameter>src</parameter>=<constant><link linkend="trig-ext">TRIG_EXT</link></constant>
919 and <parameter>arg</parameter>=<literal>3</literal>.
922 The following paragraphs discuss in somewhat more detail the trigger
923 event sources(<parameter class="function">…_src</parameter>), and the
924 corresponding arguments (<parameter class="function">…_arg</parameter>).
927 The start of an acquisition is controlled by the
928 <structfield><link linkend="command-data-struct-start-src">start_src</link></structfield> events.
929 The available options are:
934 <anchor id="trig-now-start-src"/>
935 <constant>TRIG_NOW</constant>: the <quote>start</quote> event occurs
936 <structfield><link linkend="command-data-struct-start-arg">start_arg</link></structfield>
937 nanoseconds after the command is set up. Currently, only
938 <structfield><link linkend="command-data-struct-start-arg">start_arg</link></structfield>=<literal>0</literal> is
945 <anchor id="trig-follow-start-src"/>
946 <constant>TRIG_FOLLOW</constant>: (For an output device.) The <quote>start</quote>
947 event occurs when data is written to the buffer.
953 <anchor id="trig-ext-start-src"/>
954 <constant>TRIG_EXT</constant>: the <quote>start</quote> event occurs when an
955 external trigger signal occurs; e.g., a rising edge of a digital line.
956 <structfield><link linkend="command-data-struct-start-arg">start_arg</link></structfield>
957 chooses the particular digital line.
963 <anchor id="trig-int-start-src"/>
964 <constant>TRIG_INT</constant>: the <quote>start</quote> event occurs on a &comedi;
965 internal signal, which is typically caused by an
966 <constant><link linkend="insn-inttrig">INSN_INTTRIG</link></constant>
972 The start of the beginning of each
973 <link linkend="scan">scan</link> is controlled by the
974 <structfield><link linkend="command-data-struct-scan-begin-src">scan_begin_src</link></structfield> events.
975 The available options are:
980 <anchor id="trig-timer-start-scan"/>
981 <constant>TRIG_TIMER</constant>: <quote>scan begin</quote>
982 events occur periodically. The time between <quote>scan begin</quote>
984 <structfield><link linkend="command-data-struct-scan-begin-arg">scan_begin_arg</link></structfield>
991 <anchor id="trig-follow-start-scan"/>
992 <constant>TRIG_FOLLOW</constant>: The <quote>scan begin</quote>
993 event occurs immediately after a <quote>scan end</quote>
1000 <anchor id="trig-ext-start-scan"/>
1001 <constant>TRIG_EXT</constant>: the <quote>scan begin</quote>
1002 event occurs when an external trigger signal
1003 occurs; e.g., a rising edge of a digital line.
1004 <structfield><link linkend="command-data-struct-scan-begin-arg">scan_begin_arg</link></structfield>
1005 chooses the particular digital line.
1011 <structfield><link linkend="command-data-struct-scan-begin-arg">scan_begin_arg</link></structfield>
1012 used here may not be supported exactly by the device, but it
1013 will be adjusted to the nearest supported value by
1014 <function><link linkend="func-ref-comedi-command-test">comedi_command_test</link></function>.
1017 The timing between each sample in a
1018 <link linkend="scan">scan</link> is controlled by the
1019 <structfield><link linkend="command-data-struct-convert-src">convert_src</link></structfield>
1021 The available options are:
1026 <anchor id="convert-trig-timer"/>
1027 <anchor id="trig-timer"/>
1028 <constant>TRIG_TIMER</constant>: the conversion events occur periodically.
1029 The time between <quote>convert</quote> events is
1030 <structfield><link linkend="command-data-struct-convert-arg">convert_arg</link></structfield>
1037 <anchor id="convert-trig-ext"/>
1038 <anchor id="trig-ext"/>
1039 <constant>TRIG_EXT</constant>: the conversion events occur when an
1040 external trigger signal occurs, e.g., a rising edge of a digital line.
1041 <structfield><link linkend="command-data-struct-convert-arg">convert_arg</link></structfield>
1042 chooses the particular digital line.
1048 <anchor id="convert-trig-now"/>
1049 <anchor id="trig-now"/>
1050 <constant>TRIG_NOW</constant>: All conversion events in a
1051 <link linkend="scan">scan</link> occur simultaneously.
1056 The <emphasis>end</emphasis> of each scan is almost always specified
1058 <structfield><link linkend="command-data-struct-scan-end-src">scan_end_src</link></structfield>
1060 <constant><link linkend="trig-count">TRIG_COUNT</link></constant>,
1061 with the argument being the same as the number of channels in the
1062 <structfield><link linkend="command-data-struct-chanlist">chanlist</link></structfield>. You
1063 could probably find a device that allows something else, but it would
1068 <link linkend="acquisitionterminology">acquisition</link> is
1070 <structfield><link linkend="command-data-struct-stop-src">stop_src</link></structfield> event.
1071 The available options are:
1076 <anchor id="acquisition-end-trig-count"/>
1077 <anchor id="trig-count"/>
1078 <constant>TRIG_COUNT</constant>: stop the acquisition after
1079 <structfield><link linkend="command-data-struct-stop-arg">stop_arg</link></structfield>
1086 <anchor id="acquisition-end-trig-none"/>
1087 <anchor id="trig-none"/>
1088 <constant>TRIG_NONE</constant>: perform continuous acquisition,
1090 <function><link linkend="func-ref-comedi-cancel">comedi_cancel</link></function>.
1093 Its <structfield>stop_arg</structfield> argument is reserved and should be set to <literal>0</literal>.
1094 (<quote>Reserved</quote>
1095 means that unspecified things could happen if it is set to something
1096 else but <literal>0</literal>.)
1101 There are a couple of less usual or not yet implemented events:
1106 <anchor id="trig-time"/>
1107 <constant>TRIG_TIME</constant>:
1108 cause an event to occur at a particular time.
1111 (This event source is reserved for future use.)
1117 <anchor id="trigother-event"/>
1118 <constant>TRIG_OTHER</constant>: driver specific event trigger.
1121 This event can be useful as any of the trigger sources. Its exact
1122 meaning is driver specific, because it implements a feature that
1123 otherwise does not fit into the generic &comedi; command interface.
1124 Configuration of <constant>TRIG_OTHER</constant> features are done by
1125 <constant><link linkend="instructionsconfiguration">INSN_CONFIG</link></constant>
1129 The argument is reserved and should be set to <literal>0</literal>.
1134 Not all event sources are applicable to all events. Supported
1135 trigger sources for specific events depend significantly on your
1136 particular device, and even more on the current state of its device
1138 <function><link linkend="func-ref-comedi-get-cmd-src-mask">comedi_get_cmd_src_mask</link></function>
1139 function is useful for determining what trigger sources a subdevice
1146 <section id="comedicmdflags">
1149 <anchor id="source.flags.anchor"/>
1154 <structfield><link linkend="command-data-struct-flags">flags</link></structfield>
1156 <link linkend="ref-type-comedi-cmd">command data structure</link>
1157 is used to specify some <quote>behaviour</quote> of the acquisitions in
1159 The meaning of the field is as follows:
1164 <anchor id="trig-rt"/>
1165 <constant>TRIG_RT</constant>: ask the driver to use a
1166 <emphasis role="strong">hard real-time</emphasis> interrupt handler.
1167 This will reduce latency in handling interrupts from your data
1169 hardware. It can be useful if you are sampling at high frequency, or
1170 if your hardware has a small onboard data buffer. You must have a
1171 real-time kernel (<ulink url="http://www.rtai.org">RTAI</ulink> or
1172 <ulink url="http://www.rtlinux-gpl.org/">RTLinux/GPL</ulink>)
1173 and must compile &comedi; with real-time support, or this flag will do
1180 <anchor id="trig-wake-eos"/>
1181 <constant>TRIG_WAKE_EOS</constant>:
1182 where <quote>EOS</quote> stands for <quote>End of Scan</quote>. Some
1183 drivers will change their behaviour when this flag is set, trying to
1184 transfer data at the end of every scan (instead of, for example,
1185 passing data in chunks whenever the board's hardware data buffer is
1186 half full). This flag may degrade a driver's performance at high
1187 frequencies, because the end of a scan is, in general, a much more
1188 frequent event than the filling up of the data buffer.
1194 <anchor id="trig-round-nearest"/>
1195 <constant>TRIG_ROUND_NEAREST</constant>:
1196 round to nearest supported timing period, the default.
1197 This flag (as well as the following three), indicates how timing
1198 arguments should be rounded if the hardware cannot achieve the exact
1205 <anchor id="trig-round-down"/>
1206 <constant>TRIG_ROUND_DOWN</constant>: round period down.
1212 <anchor id="trig-round-up"/>
1213 <constant>TRIG_ROUND_UP</constant>: round period up.
1219 <anchor id="trig-round-up-next"/>
1220 <constant>TRIG_ROUND_UP_NEXT</constant>:
1221 this one doesn't do anything, and I don't know what it was intended
1228 <anchor id="trig-dither"/>
1229 <constant>TRIG_DITHER</constant>: enable dithering? Dithering is
1230 a software technique to smooth the influence of discretization
1231 <quote>noise</quote>.
1237 <anchor id="trig-deglitch"/>
1238 <constant>TRIG_DEGLITCH</constant>: enable deglitching?
1239 Another <quote>noise</quote> smoothing technique.
1245 <anchor id="trig-write"/>
1246 <constant>TRIG_WRITE</constant>:
1247 write to bidirectional devices. Could be useful, in principle, if
1248 someone wrote a driver that supported commands for a digital I/O
1249 device that could do either input or output.
1255 <anchor id="trig-bogus"/>
1256 <constant>TRIG_BOGUS</constant>: do the motions?
1262 <anchor id="trig-other"/>
1263 <constant>TRIG_CONFIG</constant>: perform configuration, not triggering.
1264 This is a legacy of the deprecated
1265 <type><link linkend="ref-type-comedi-trig">comedi_trig_struct</link></type>
1266 data structure, and has no function at present.
1280 If you wish to aquire accurate waveforms, it is vital that you use an
1281 anti-alias filter. An anti-alias filter is a low-pass filter used to
1282 remove all frequencies higher than the Nyquist frequency (half your sampling rate)
1283 from your analog input signal
1284 before you convert it to digital. If you fail to filter your input signal,
1285 any high frequency components in the original analog signal will create
1286 artifacts in your recorded digital waveform that cannot be corrected.
1289 For example, suppose you are sampling an analog input channel at a rate of
1290 1000 Hz. If you were to apply a 900 Hz sine wave to the input, you
1291 would find that your
1292 sampling rate is not high enough to faithfully record the 900 Hz input,
1293 since it is above your Nyquist frequency of 500 Hz. Instead, what you
1294 will see in your recorded digital waveform is a 100 Hz sine wave! If you
1295 don't use an anti-alias filter, it is impossible to tell whether the 100
1296 Hz sine wave you see in your digital signal was really produced by a
1297 100 Hz input signal, or a 900 Hz signal aliased to 100 Hz, or a 1100 Hz
1301 In practice, the cutoff frequency for the anti-alias filter is usually
1302 set 10% to 20% below the Nyquist frequency due to fact that real filters
1303 do not have infinitely sharp cutoffs.
1309 <section id="slowlyvarying">
1311 Slowly-varying inputs
1315 <emphasis role="strong">Note: The functions described here use an old
1316 feature that is no longer implemented by the &comedi;
1317 kernel layer. THEY WILL NOT WORK!</emphasis>
1321 Sometimes, your input channels change slowly enough that
1322 you are able to average many successive input values to get a
1323 more accurate measurement of the actual value. In general,
1324 the more samples you average, the better your estimate
1325 gets, roughly by a factor of
1326 <function>sqrt<parameter>number_of_samples</parameter></function>.
1327 Obviously, there are limitations to this:
1334 you are ultimately limited by <quote>Spurious Free Dynamic
1335 Range</quote>. This SFDR is one of the popular measures to quantify how
1336 much noise a signal carries. If you take a Fourier transform of your
1337 signal, you will see several <quote>peaks</quote> in the transform: one
1338 or more of the fundamental harmonics of the measured signal, and lots
1339 of little <quote>peaks</quote> (called <quote>spurs</quote>) caused by
1340 noise. The SFDR is then the difference between the amplitude of the
1341 fundamental harmonic and of the largest spur (at frequencies below
1342 half of the Nyquist frequency of the DAQ sampler!).
1348 you need to have <emphasis>some</emphasis> noise on the input channel,
1349 otherwise you will be averaging the same number <literal>N</literal>
1350 times. (Of course, this only holds if the noise is large enough to
1351 cause at least a one-bit discretization.)
1357 the more noise you have, the greater your SFDR, but it
1358 takes many more samples to compensate for the increased
1365 if you feel the need to average samples for, for example, two seconds,
1366 your signal will need to be <emphasis>very</emphasis> slowly-varying,
1367 i.e., not varying more than your target uncertainty for the entire two
1375 As you might have guessed, the &comedi; library has functions
1376 to help you in your quest to accurately measure slowly varying
1379 <funcsynopsis><funcprototype>
1380 <funcdef>int <function>comedi_sv_init</function></funcdef>
1381 <paramdef>comedi_sv_t *<parameter>sv</parameter></paramdef>
1382 <paramdef>comedi_t *<parameter>device</parameter></paramdef>
1383 <paramdef>unsigned int <parameter>subdevice</parameter></paramdef>
1384 <paramdef>unsigned int <parameter>channel</parameter></paramdef>
1385 </funcprototype></funcsynopsis>
1387 The above function <function><link linkend="func-ref-comedi-sv-init">comedi_sv_init</link></function> initializes the
1388 <type><link linkend="ref-type-comedi-sv-t">comedi_sv_t</link></type> data structure, used
1389 to do the averaging acquisition:
1391 typedef struct comedi_sv_struct {
1392 <link linkend="ref-type-comedi-t">comedi_t</link> *dev;
1393 unsigned int subdevice;
1400 /* number of measurements to average (for analog inputs) */
1407 The actual acquisition is done with the function
1408 <function><link linkend="func-ref-comedi-sv-measure">comedi_sv_measure</link></function>:
1410 <funcsynopsis><funcprototype>
1411 <funcdef>int <function>comedi_sv_measure</function></funcdef>
1412 <paramdef>comedi_sv_t *<parameter>sv</parameter></paramdef>
1413 <paramdef>double *<parameter>data</parameter></paramdef>
1414 </funcprototype></funcsynopsis>
1416 The number of samples over which the function
1417 <function>comedi_sv_measure</function> averages is limited by the
1418 implementation (currently the limit is 100 samples).
1422 One typical use for this function is the measurement of thermocouple
1424 And the &comedi; self-calibration utility also uses these functions.
1425 On some hardware, it is possible to tell it to measure an
1426 internal stable voltage reference, which is typically going
1427 to be very slowly varying; on the kilosecond time scale
1428 or more. So, it is reasonable to measure millions of samples,
1429 to get a very accurate measurement of the A/D converter output
1430 value that corresponds to the voltage reference. Sometimes,
1431 however, this is overkill, since there is no need to
1432 perform a part-per-million calibration to a standard that
1433 is only accurate to a part-per-thousand.
1438 <section id="experimentalfunctionality">
1440 Experimental functionality
1444 The following subsections document functionality that has not yet
1445 matured. Most of this functionality has even not been implemented yet
1446 in any single device driver. This information is included here, in
1447 order to stimulate discussion about their API, and to encourage
1448 pioneering implementations.
1451 <section id="digitalinputcombining">
1453 Digital input combining machines
1457 (<emphasis role="strong">Status: experimental (i.e., no driver implements
1458 this yet)</emphasis>)
1461 When one or several digital inputs are used to modify an output
1462 value, either an accumulator or a single digital line or bit,
1463 a bitfield structure is typically used in the &comedi; interface.
1464 The digital inputs have two properties, <quote>sensitive</quote> inputs
1465 and <quote>modifier</quote> inputs. Edge transitions on sensitive
1466 inputs cause changes in the output signal, whereas modifier inputs
1467 change the effect of edge transitions on sensitive inputs. Note that
1468 inputs can be both modifier inputs and sensitive inputs.
1472 For simplification purposes, it is assumed that multiple digital
1473 inputs do not change simultaneously.
1477 The combined state of the modifier inputs determine a modifier
1478 state. For each combination of modifier state and sensitive
1479 input, there is a set of bits that determine the effect on the
1480 output value due to positive or negative transitions of the
1481 sensitive input. For each transition direction, there are two
1482 bits defined as follows:
1484 <variablelist spacing="compact">
1487 <listitem>transition is ignored.</listitem>
1491 <listitem>accumulator is incremented, or output is set.</listitem>
1495 <listitem>accumulator is decremented, or output is cleared.</listitem>
1499 <listitem>reserved.</listitem>
1503 For example, a simple digital follower is specified by the bit
1504 pattern 01 10, because it sets the output on positive transitions
1505 of the input, and clears the output on negative transitions. A
1506 digital inverter is similarily 10 01. These systems have only
1507 one sensitive input.
1511 As another example, a simple up counter, which increments on
1512 positive transitions of one input, is specified by 01 00. This
1513 system has only one sensitive input.
1517 When multiple digital inputs are used, the inputs are divided
1518 into two types, inputs which cause changes in the accumulator, and
1519 those that only modify the meaning of transitions on other inputs.
1520 Modifier inputs do not require bitfields, but there needs to be
1521 a bitfield of length 4*(2^(N-1)) for each edge sensitive input,
1522 where N is the total number of inputs. Since N is usually 2 or
1523 3, with only one edge sensitive input, the scaling issues are
1530 <section id="analogconversion">
1532 Analog filtering configuration
1536 <emphasis role="strong">(Status: design (i.e., no driver implements
1537 this yet).)</emphasis>
1541 The <structfield><link linkend="insn-data-structure-insn">insn</link></structfield>
1543 <link linkend="insn-data-structure">instruction data structure</link>
1544 has not been assigned yet.
1547 The <structfield><link linkend="insn-data-structure-chanspec">chanspec</link></structfield> field
1548 of the <link linkend="insn-data-structure">instruction data
1549 structure</link> is ignored.
1553 Some devices have the capability to add white noise (dithering) to
1554 analog input measurement. This additional noise can then be averaged
1555 out, to get a more accurate measurement of the input signal. It
1556 should not be assumed that channels can be separately configured.
1557 A simple design can use 1 bit to turn this feature on/off.
1561 Some devices have the capability of changing the glitch characteristics
1562 of analog output subsytems. The default (off) case should be where
1563 the average settling time is lowest. A simple design can use 1 bit
1564 to turn this feature on/off.
1568 Some devices have a configurable analog filters as part of the analog
1569 input stage. A simple design can use 1 bit to enable/disable the
1570 filter. Default is disabled, i.e., the filter being bypassed, or if
1571 the choice is between two filters, the filter with the largest
1576 <section id="waveformgeneration">
1578 Analog Output Waveform Generation
1582 <emphasis role="strong">(Status: design (i.e., no driver implements
1583 this yet).)</emphasis>
1586 The <structfield><link linkend="insn-data-structure-insn">insn</link></structfield> field of the
1587 <link linkend="insn-data-structure">instruction data structure</link>
1588 has not been assigned yet.
1591 The <structfield><link linkend="insn-data-structure-chanspec">chanspec</link></structfield> field
1592 of the <link linkend="insn-data-structure">instruction data
1593 structure</link> is ignored.
1597 Some devices have the ability to cyclicly loop through samples kept in
1598 an on-board analog output FIFO. This config should allow the user to
1599 enable/disable this mode.
1603 This config should allow the user to configure the number of samples
1604 to loop through. It may be necessary to configure the channels used.
1609 <section id="extendedtriggering">
1614 <emphasis role="strong">(Status: alpha.)</emphasis>
1618 The <structfield><link linkend="insn-data-structure-insn">insn</link></structfield> field of the
1619 <link linkend="insn-data-structure">instruction data structure</link>
1620 has not been assigned yet.
1623 The <structfield><link linkend="insn-data-structure-chanspec">chanspec</link></structfield> field
1624 of the <link linkend="insn-data-structure">instruction data
1625 structure</link> is ignored.
1629 This section covers common information for all extended
1630 triggering configuration, and doesn't describe a particular
1631 type of extended trigger.
1635 Extended triggering is used to configure triggering engines that
1636 do not fit into commands. In a typical programming sequence, the
1637 application will use
1638 <link linkend="instructionsconfiguration">configuration instructions</link>
1639 to configure an extended trigger, and a
1640 <link linkend="commandsstreaming">command</link>,
1642 <constant><link linkend="trig-other">TRIG_OTHER</link></constant>
1643 as one of the trigger sources.
1647 Extended trigger configuration should be designed in such a way
1648 that the user can probe for valid parameters, similar to how
1649 command testing works. An extended trigger configuration instruction
1650 should not configure the hardware directly, rather, the configuration
1651 should be saved until the subsequent command is issued. This
1652 allows more flexibility for future interface changes.
1656 It has not been decided whether the configuration stage should return a
1657 token that is then used as the trigger argument in the command.
1658 Using tokens is one method to satisfy the problem that extended
1659 trigger configurations may have subtle compatiblity issues with
1660 other trigger sources/arguments that can only be determined at
1661 command test time. Passing all stages of a command test should
1662 only be allowed with a properly configured extended trigger.
1666 Extended triggers must use
1667 <structfield><link linkend="insn-data-structure-data">data</link></structfield>[1] as flags. The
1668 upper 16 bits are reserved and used only for flags that are common to
1669 all extended triggers. The lower 16 bits may be defined by the
1670 particular type of extended trigger.
1674 Various types of extended triggers must use
1675 <structfield><link linkend="insn-data-structure-data">data</link></structfield>[1] to know which
1676 event the extended trigger will be assigned to in the command
1677 structure. The possible values are an OR'd mask of the following:
1683 <constant>COMEDI_EV_START</constant>
1688 <constant>COMEDI_EV_SCAN_BEGIN</constant>
1693 <constant>COMEDI_EV_CONVERT</constant>
1698 <constant>COMEDI_EV_SCAN_END</constant>
1703 <constant>COMEDI_EV_STOP</constant>
1710 <section id="analogtriggering">
1715 <emphasis role="strong">
1716 (Status: alpha. The <filename>ni_mio_common.c</filename> driver
1717 implements this feature.)
1722 The <structfield><link linkend="insn-data-structure-insn">insn</link></structfield> field of the
1723 <link linkend="insn-data-structure">instruction data structure</link>
1724 has not been assigned yet.
1727 The <structfield><link linkend="insn-data-structure-chanspec">chanspec</link></structfield> field
1728 of the <link linkend="insn-data-structure">instruction data
1729 structure</link> is ignored.
1733 The <structfield><link linkend="insn-data-structure-data">data</link></structfield> field
1734 of the <link linkend="insn-data-structure">instruction data
1735 structure</link> is used as follows:
1736 <variablelist spacing="compact">
1738 <term>data[1]</term>
1739 <listitem>trigger and combining machine configuration.</listitem>
1742 <term>data[2]</term>
1743 <listitem>analog triggering signal chanspec.</listitem>
1746 <term>data[3]</term>
1747 <listitem>primary analog level.</listitem>
1750 <term>data[4]</term>
1751 <listitem>secondary analog level.</listitem>
1756 Analog triggering is described by a digital combining machine that
1757 has two sensitive digital inputs. The sensitive digital inputs are
1758 generated by configurable analog comparators. The analog comparators
1759 generate a digital 1 when the analog triggering signal is greater
1760 than the comparator level. The digital inputs are not modifier
1761 inputs. Note, however, there is an effective modifier due to the
1762 restriction that the primary analog comparator level must be less
1763 than the secondary analog comparator level.
1767 If only one analog comparator signal is used, the combining machine
1768 for the secondary input should be set to ignored, and the secondary
1769 analog level should be set to <literal>0</literal>.
1773 The interpretation of the chanspec and voltage levels is device
1774 dependent, but should correspond to similar values of the analog
1775 input subdevice, if possible.
1779 Notes: Reading range information is not addressed. This makes it
1780 difficult to convert comparator voltages to data values.
1784 Possible extensions: A parameter that specifies the necessary time
1785 that the set condition has to be true before the trigger is generated.
1786 A parameter that specifies the necessary time that the reset condition
1787 has to be true before the state machine is reset.
1792 <section id="bitfieldmatching">
1794 Bitfield Pattern Matching Extended Trigger
1797 <emphasis role="strong">
1798 (Status: design. No driver implements this feature yet.)
1803 The <structfield><link linkend="insn-data-structure-insn">insn</link></structfield> field of the
1804 <link linkend="insn-data-structure">instruction data structure</link>
1805 has not been assigned yet.
1808 The <structfield><link linkend="insn-data-structure-chanspec">chanspec</link></structfield> field
1809 of the <link linkend="insn-data-structure">instruction data
1810 structure</link> is ignored.
1814 The <structfield><link linkend="insn-data-structure-data">data</link></structfield> field
1815 of the <link linkend="insn-data-structure">instruction data
1816 structure</link> is used as follows:
1818 <variablelist spacing="compact">
1820 <term>data[1]</term>
1821 <listitem>trigger flags.</listitem>
1824 <term>data[2]</term>
1825 <listitem>mask.</listitem>
1828 <term>data[3]</term>
1829 <listitem>pattern.</listitem>
1834 The pattern matching trigger issues a trigger when all of a specifed
1835 set of input lines match a specified pattern. If the device allows,
1836 the input lines should correspond to the input lines of a digital input
1837 subdevice, however, this will necessarily be device dependent. Each
1838 possible digital line that can be matched is assigned a bit in the
1839 mask and pattern. A bit set in the mask indicates that the
1840 input line must match the corresponding bit in the pattern.
1841 A bit cleared in the mask indicates that the input line is ignored.
1845 Notes: This only allows 32 bits in the pattern/mask, which may be
1846 too few. Devices may support selecting different sets of lines from
1847 which to match a pattern.
1851 Discovery: The number of bits can be discovered by setting the mask
1852 to all 1's. The driver must modify this value and return
1853 <constant>-EAGAIN</constant>.
1858 <section id="countertimer">
1860 Counter configuration
1863 <emphasis role="strong">
1864 (Status: design. No driver implements this feature yet.)
1869 The <structfield><link linkend="insn-data-structure-insn">insn</link></structfield> field of the
1870 <link linkend="insn-data-structure">instruction data structure</link>
1871 has not been assigned yet.
1874 The <structfield><link linkend="insn-data-structure-chanspec">chanspec</link></structfield> field
1875 of the <link linkend="insn-data-structure">instruction data
1876 structure</link> is used to specify which counter to use. (I.e., the
1877 counter is a &comedi; channel.)
1881 The <structfield><link linkend="insn-data-structure-data">data</link></structfield> field
1882 of the <link linkend="insn-data-structure">instruction data
1883 structure</link> is used as follows:
1885 <variablelist spacing="compact">
1887 <term>data[1]</term>
1888 <listitem>trigger configuration.</listitem>
1891 <term>data[2]</term>
1892 <listitem>primary input chanspec.</listitem>
1895 <term>data[3]</term>
1896 <listitem>primary combining machine configuration.</listitem>
1899 <term>data[4]</term>
1900 <listitem>secondary input chanspec.</listitem>
1903 <term>data[5]</term>
1904 <listitem>secondary combining machine configuration.</listitem>
1907 <term>data[6]</term>
1908 <listitem>latch configuration.</listitem>
1913 Note that this configuration is only useful if the counting has to be
1914 done in <emphasis>software</emphasis>. Many cards offer configurable
1915 counters in hardware; e.g., general purpose timer cards can be
1916 configured to act as pulse generators, frequency counters, timers,
1920 Counters can be operated either in synchronous mode (using
1921 <constant><link linkend="insn-read">INSN_READ</link></constant>)
1922 or asynchronous mode (using
1923 <link linkend="commandsstreaming">commands</link>), similar to analog
1925 The input signal for both modes is the accumulator.
1926 Commands on counter subdevices are almost always specified using
1927 <structfield><link linkend="command-data-struct-scan-begin-src">scan_begin_src</link></structfield>
1928 = <constant><link linkend="trigother-event">TRIG_OTHER</link></constant>,
1929 with the counter configuration also serving as the extended configuration for
1930 the <quote>scan begin</quote> source.
1934 Counters are made up of an accumulator and a combining machine that
1935 determines when the accumulator should be incremented or decremented
1936 based on the values of the input signals. The combining machine
1937 optionally determines when the accumulator should be latched and
1938 put into a buffer. This feature is used in asynchronous mode.
1942 Note: How to access multiple pieces of data acquired at each event?
1947 <section id="auxcounter">
1949 One source plus auxiliary counter configuration
1952 <emphasis role="strong">
1953 (Status: design. No driver implements this feature yet.)
1958 The <structfield><link linkend="insn-data-structure-insn">insn</link></structfield> field of the
1959 <link linkend="insn-data-structure">instruction data structure</link>
1960 has not been assigned yet.
1963 The <structfield><link linkend="insn-data-structure-chanspec">chanspec</link></structfield> field
1964 of the <link linkend="insn-data-structure">instruction data
1965 structure</link> is used to …
1969 The <structfield><link linkend="insn-data-structure-data">data</link></structfield> field
1970 of the <link linkend="insn-data-structure">instruction data
1971 structure</link> is used as follows:
1975 <variablelist spacing="compact">
1977 <term>data[1]</term>
1979 is flags, including the flags for the command triggering
1980 configuration. If a command is not subsequently issued on the
1981 subdevice, the command triggering portion of the flags are ignored.
1985 <term>data[2]</term>
1987 determines the mode of operation. The mode of operation
1988 is actually a bitfield that encodes what to do for various
1989 transitions of the source signals.
1993 <term>data[3]</term>
1994 <term>data[4]</term>
1996 determine the primary source for the counter, similar to the
1997 <structfield><link linkend="command-data-struct-scan-begin-src">…_src</link></structfield> and the
1998 <structfield><link linkend="command-data-struct-scan-begin-arg">…_arg</link></structfield> fields
2000 <link linkend="command-data-struct">command data structure</link>.
2007 Notes: How to specify which events cause a latch and push, and what
2015 National instruments RTSI trigger bus
2018 A number of NI boards support the RTSI (Real Time System Integration) bus.
2019 It's primary use is to synchronize multiple DAQ cards.
2020 On PXI boards, the RTSI lines correspond to the PXI trigger lines 0 to 7. PCI
2021 boards use cables to connect to their RTSI ports.
2022 The RTSI bus consists of 8 digital signal lines numbered 0 to 7 that are bi-directional.
2023 Each of these signal lines
2024 can be configured as an input or output, and the signal appearing on the output
2025 of each line can be configured to one of several internal board timing signals
2026 (although on older boards RTSI line 7 can only be used for the clock signal).
2027 The <systemitem>ni_pcimio</systemitem>, <systemitem>ni_atmio</systemitem>, and
2028 <systemitem>ni_mio_cs</systemitem> drivers expose the RTSI bus
2029 as a digital I/O subdevice (subdevice number 10).
2032 The functions <function>comedi_dio_config</function> and
2033 <function>comedi_dio_get_config</function> can be used on
2034 the RTSI subdevice to
2035 set/query the direction (input or output) of each of the RTSI lines individually.
2038 The subdevice also supports the
2039 <constant>INSN_CONFIG_SET_CLOCK_SRC</constant> and
2040 <constant>INSN_CONFIG_GET_CLOCK_SRC</constant> configuration
2041 instructions, which can be
2042 used to configure/query what source the board uses to synchronize its
2043 master clock to. The various possibilities are defined in the <filename>comedi.h</filename>
2047 <tgroup cols='2' align='left'>
2050 <entry>Clock Source</entry>
2051 <entry>Description</entry>
2056 <entry><constant>NI_MIO_INTERNAL_CLOCK</constant></entry>
2058 Use the board's internal oscillator.
2062 <entry><constant>NI_MIO_RTSI_CLOCK</constant></entry>
2064 Use the RTSI line 7 as the master clock. This source is
2065 only supported on pre-m-series boards. The newer m-series boards
2066 use <function>NI_MIO_PLL_RTSI_CLOCK</function> instead.
2070 <entry><constant>NI_MIO_PLL_PXI_STAR_TRIGGER_CLOCK</constant></entry>
2072 Only available for newer m-series PXI boards. Synchronizes the board's
2073 phased-locked loop (which runs at 80MHz) to the PXI star trigger
2078 <entry><constant>NI_MIO_PLL_PXI10_CLOCK</constant></entry>
2080 Only available for newer m-series PXI boards.
2081 Synchronizes the board's
2082 phased-locked loop (which runs at 80MHz) to the 10 MHz PXI backplane
2088 <function>NI_MIO_PLL_RTSI_CLOCK<parameter>n</parameter></function>
2091 Only available for newer m-series boards.
2092 The function returns a clock source which will cause the board's
2093 phased-locked loop (which runs at 80MHz) to syncronize to the RTSI
2094 line specified in the function argument.
2102 For all clock sources except <constant>NI_MIO_INTERNAL_CLOCK</constant>
2103 and <constant>NI_MIO_PLL_PXI10_CLOCK</constant>,
2104 you should pass the period of the clock your are feeding to the board when
2105 using <constant>INSN_CONFIG_SET_CLOCK_SRC</constant>.
2108 Finally, the configuration instructions
2109 <constant>INSN_CONFIG_SET_ROUTING</constant> and
2110 <constant>INSN_CONFIG_GET_ROUTING</constant>
2111 can be used to select/query which internal signal
2112 will appear on a given RTSI output line. The header file <filename>comedi.h</filename> defines
2113 the following signal sources which can be routed to an RTSI line:
2117 <tgroup cols='2' align='left'>
2120 <entry>Signal Source</entry>
2121 <entry>Description</entry>
2126 <entry><constant>NI_RTSI_OUTPUT_ADR_START1</constant></entry>
2128 ADR_START1, an analog input start signal. See the NI's
2129 DAQ-STC Technical Reference Manual for more information.
2133 <entry><constant>NI_RTSI_OUTPUT_ADR_START2</constant></entry>
2135 ADR_START2, an analog input stop signal. See the NI's
2136 DAQ-STC Technical Reference Manual for more information.
2140 <entry><constant>NI_RTSI_OUTPUT_SCLKG</constant></entry>
2142 SCLKG, a sample clock signal. See the NI's
2143 DAQ-STC Technical Reference Manual for more information.
2147 <entry><constant>NI_RTSI_OUTPUT_DACUPDN</constant></entry>
2149 DACUPDN, a dac update signal. See the NI's
2150 DAQ-STC Technical Reference Manual for more information.
2154 <entry><constant>NI_RTSI_OUTPUT_DA_START1</constant></entry>
2156 DA_START1, an analog output start signal. See the NI's
2157 DAQ-STC Technical Reference Manual for more information.
2161 <entry><constant>NI_RTSI_OUTPUT_G_SRC0</constant></entry>
2163 G_SRC0, the source signal to general purpose counter 0. See the NI's
2164 DAQ-STC Technical Reference Manual for more information.
2168 <entry><constant>NI_RTSI_OUTPUT_G_GATE0</constant></entry>
2170 G_GATE0, the gate signal to general purpose counter 0. See the NI's
2171 DAQ-STC Technical Reference Manual for more information.
2175 <entry><constant>NI_RTSI_OUTPUT_RGOUT0</constant></entry>
2177 RGOUT0, the output signal of general purpose counter 0. See the NI's
2178 DAQ-STC Technical Reference Manual for more information.
2183 <function>NI_RTSI_OUTPUT_RTSI_BRD<parameter>n</parameter></function>
2186 RTSI_BRD0 though RTSI_BRD3 are four internal signals which can
2187 have various other signals routed to them in turn. Currently, comedi
2188 provides no way to configure the signals routed to the RTSI_BRD lines.
2189 See the NI's DAQ-STC Technical Reference Manual for more information.
2193 <entry><constant>NI_RTSI_OUTPUT_RTSI_OSC</constant></entry>
2195 The RTSI clock signal. On pre-m-series boards, this signal is always
2196 routed to RTSI line 7, and cannot be routed to lines 0 through 6. On
2197 m-series boards, any RTSI line can be configured to output the clock
2206 The RTSI bus pins may be used as trigger inputs for many of the
2207 &comedi; trigger functions. To use the RTSI bus pins, set the source to be
2208 <constant>TRIG_EXT</constant> and the source argument using the return values
2209 from the <function>NI_EXT_RTSI<parameter>n</parameter></function> function (or similarly the
2210 <function>NI_EXT_PFI<parameter>n</parameter></function> function if you want
2211 to trigger from a PFI line). The <constant>CR_EDGE</constant> and
2212 <constant>CR_INVERT</constant> flags may
2213 also be set on the trigger source argument to specify edge and
2214 falling edge/low level triggering.
2218 An example to set up a device as a master is given below.
2221 <programlisting><![CDATA[
2222 void comediEnableMaster(comedi_t *dev){
2223 comedi_insn configCmd;
2224 lsampl_t configData[2];
2227 static const unsigned rtsi_subdev = 10;
2228 static const unsigned rtsi_clock_line = 7;
2230 /* Route RTSI clock to line 7 (not needed on pre-m-series boards since their
2231 clock is always on line 7). */
2232 memset(&configCmd, 0, sizeof(configCmd));
2233 memset(&configData, 0, sizeof(configData));
2234 configCmd.insn = INSN_CONFIG;
2235 configCmd.subdev = rtsi_subdev;
2236 configCmd.chanspec = rtsi_clock_line;
2238 configCmd.data = configData;
2239 configCmd.data[0] = INSN_CONFIG_SET_ROUTING;
2240 configCmd.data[1] = NI_RTSI_OUTPUT_RTSI_OSC;
2241 ret = comedi_do_insn(dev, &configCmd);
2243 comedi_perror("comedi_do_insn: INSN_CONFIG");
2246 // Set clock RTSI line as output
2247 ret = comedi_dio_config(dev, rtsi_subdev, rtsi_clock_line, INSN_CONFIG_DIO_OUTPUT);
2249 comedi_perror("comedi_dio_config");
2253 /* Set routing of the 3 main AI RTSI signals and their direction to output.
2254 We're reusing the already initialized configCmd instruction here since
2255 it's mostly the same. */
2256 configCmd.chanspec = 0;
2257 configCmd.data[1] = NI_RTSI_OUTPUT_ADR_START1;
2258 ret = comedi_do_insn(dev, &configCmd);
2260 comedi_perror("comedi_do_insn: INSN_CONFIG");
2263 ret = comedi_dio_config(dev, rtsi_subdev, 0, INSN_CONFIG_DIO_OUTPUT);
2265 comedi_perror("comedi_dio_config");
2269 configCmd.chanspec = 1;
2270 configCmd.data[1] = NI_RTSI_OUTPUT_ADR_START2;
2271 ret = comedi_do_insn(dev, &configCmd);
2273 comedi_perror("comedi_do_insn: INSN_CONFIG");
2276 ret = comedi_dio_config(dev, rtsi_subdev, 1, INSN_CONFIG_DIO_OUTPUT);
2278 comedi_perror("comedi_dio_config");
2282 configCmd.chanspec = 2;
2283 configCmd.data[1] = NI_RTSI_OUTPUT_SCLKG;
2284 ret = comedi_do_insn(dev, &configCmd);
2286 comedi_perror("comedi_do_insn: INSN_CONFIG");
2289 ret = comedi_dio_config(dev, rtsi_subdev, 2, INSN_CONFIG_DIO_OUTPUT);
2291 comedi_perror("comedi_dio_config");
2295 ]]></programlisting>
2298 An example to slave a m-series device from this master follows. A pre-m-series
2299 device would need to use <constant>NI_MIO_RTSI_CLOCK</constant> for
2300 the clock source instead. In
2301 your code, you may also wish to configure the master device to use the
2302 external clock source instead of using its internal clock directly (for
2303 best syncronization).
2305 <programlisting><![CDATA[
2306 void comediEnableSlave(comedi_t *dev){
2307 comedi_insn configCmd;
2308 lsampl_t configData[3];
2310 unsigned int d = 0;;
2311 static const unsigned rtsi_subdev = 10;
2312 static const unsigned rtsi_clock_line = 7;
2314 memset(&configCmd, 0, sizeof(configCmd));
2315 memset(&configData, 0, sizeof(configData));
2316 configCmd.insn = INSN_CONFIG;
2317 configCmd.subdev = rtsi_subdev;
2318 configCmd.chanspec = 0;
2320 configCmd.data = configData;
2321 configCmd.data[0] = INSN_CONFIG_SET_CLOCK_SRC;
2322 configCmd.data[1] = NI_MIO_PLL_RTSI_CLOCK(rtsi_clock_line);
2323 configCmd.data[2] = 100; /* need to give it correct external clock period */
2324 ret = comedi_do_insn(dev, &configCmd);
2326 comedi_perror("comedi_do_insn: INSN_CONFIG");
2329 /* configure RTSI clock line as input */
2330 ret = comedi_dio_config(dev, rtsi_subdev, rtsi_clock_line, INSN_CONFIG_DIO_INPUT);
2332 comedi_perror("comedi_dio_config");
2335 /* Configure RTSI lines we are using for AI signals as inputs. */
2336 ret = comedi_dio_config(dev, rtsi_subdev, 0, INSN_CONFIG_DIO_INPUT);
2338 comedi_perror("comedi_dio_config");
2341 ret = comedi_dio_config(dev, rtsi_subdev, 1, INSN_CONFIG_DIO_INPUT);
2343 comedi_perror("comedi_dio_config");
2346 ret = comedi_dio_config(dev, rtsi_subdev, 2, INSN_CONFIG_DIO_INPUT);
2348 comedi_perror("comedi_dio_config");
2353 int comediSlaveStart(comedi_t *dev){
2355 unsigned int nChannels = 8;
2356 double sampleRate = 50000;
2357 unsigned int chanList[8];
2361 for(i = 0; i < nChannels; i++){
2362 chanList[i] = CR_PACK(i, 0, AREF_GROUND);
2365 memset(&cmd, 0, sizeof(cmd));
2366 ret = comedi_get_cmd_generic_timed(dev, subdevice, &cmd,
2367 (int)(1e9/(nChannels * sampleRate)));
2369 printf("comedi_get_cmd_generic_timed failed\n");
2372 cmd.chanlist = chanList;
2373 cmd.chanlist_len = nChannels;
2374 cmd.scan_end_arg = nChannels;
2375 cmd.start_src = TRIG_EXT;
2376 cmd.start_arg = CR_EDGE | NI_EXT_RTSI(0);
2377 cmd.convert_src = TRIG_EXT;
2378 cmd.convert_arg = CR_INVERT | CR_EDGE | NI_EXT_RTSI(2);
2379 cmd.stop_src = TRIG_NONE;
2381 ret = comedi_command(dev0, &cmd0);
2383 printf("comedi_command failed\n");
2388 ]]></programlisting>