Asynchronous commands
Function: comedi_cancel -- stop streaming input/output in progress
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Description:
 The function <function>comedi_cancel</function> can be used to stop a command
 previously started by
 <function><link linkend="func-ref-comedi-command">comedi_command</link></function>
 which is still in progress
 on the subdevice indicated by the parameters <parameter class="function">device</parameter>
 and <parameter class="function">subdevice</parameter>.
Returns:
 On success, <literal>0</literal> is returned.
 On failure, <literal>-1</literal> is returned.

Function: comedi_command -- start streaming input/output
Retval: int
Param: comedi_t * device
Param: comedi_cmd * command
Description:
 The function <function>comedi_command</function> starts a streaming input
 or output.  The
 command structure pointed to by <parameter class="function">command</parameter> specifies
 settings for the
 acquisition.  The command must be able to pass
 <function><link
 linkend="func-ref-comedi-command-test">comedi_command_test</link></function>
 with a return value of <literal>0</literal>, or
 <function>comedi_command</function> will fail.
 For input subdevices, sample values are read using the
 function <function>read</function> on the device file descriptor.
 For output subdevices,
 sample values are written using the function <function>write</function>.
Returns:
 On success, <literal>0</literal> is returned.
 On failure, <literal>-1</literal> is returned.

Function: comedi_command_test -- test streaming input/output configuration
Retval: int
Param: comedi_t * device
Param: comedi_cmd * command
Description:
 The function <function>comedi_command_test</function> tests the command structure pointed
 to by the parameter <parameter class="function">command</parameter> and returns an
 integer describing the
 testing stages that were successfully passed.  In addition, if elements
 of the <type>comedi_cmd</type> structure are invalid, they may be modified.  Source
 elements are modified to remove invalid source triggers.  Argument
 elements are adjusted or rounded to the nearest valid value.
Returns:
 The meanings of the return value are as follows:

 <itemizedlist>
 	<listitem>
 		<para><literal>0</literal> indicates a valid command.</para>
 	</listitem>
 	<listitem>
 		<para>
 			<literal>1</literal> indicates that one of the
			<structfield>&hellip;_src</structfield>
 			members of the command contained an
 			unsupported trigger.  The bits corresponding to the unsupported
 			triggers are zeroed.
 		</para>
 	</listitem>
 	<listitem>
 		<para>
 			<literal>2</literal> indicates that the particular combination
 			of <structfield>&hellip;_src</structfield> settings is not supported by the driver, or that
 			one of the <structfield>&hellip;_src</structfield> members has the bit corresponding to
 			multiple trigger sources set at the same time.
 		</para>
 	</listitem>
 	<listitem>
 		<para>
 			<literal>3</literal> indicates that one of the
			<structfield>&hellip;_arg</structfield> members
 			of the command is set outside the range of allowable values.
 			For instance, an argument for a
			<constant>TRIG_TIMER</constant> source which
 			exceeds the board's maximum speed.  The invalid
			<structfield>&hellip;_arg</structfield>
 			members will be adjusted to valid values.
 		</para>
 	</listitem>
 	<listitem>
 		<para>
 			<literal>4</literal> indicates that one of the
			<structfield>&hellip;_arg</structfield> members
 			required adjustment.  For instance, the argument of a
 			<constant>TRIG_TIMER</constant> source may have been rounded to the nearest
 			timing period supported by the board.
 		</para>
 	</listitem>
 	<listitem>
 		<para>
 			<literal>5</literal> indicates that some aspect of the
 			command's <structfield>chanlist</structfield> is unsupported by the board.  For example,
 			some analog input boards require that all channels in the chanlist
 			use the same input range.
 		</para>
 	</listitem>
 </itemizedlist>
 On failure, <literal>-1</literal> is returned.

Function: comedi_get_buffer_contents -- streaming buffer status
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Description:
 The function <function>comedi_get_buffer_contents</function> is used on a subdevice
 that has a Comedi command in progress to get the number of unread bytes.  For
 a streaming input command, this is the number of bytes that can be read.  For
 a streaming output command, subtracting this from the buffer size gives the
 space available to be written.
Returns:
  On success, <function>comedi_get_buffer_contents</function> returns the
  number of unread bytes in the buffer.
  On failure, <literal>-1</literal> is returned.

Function: comedi_get_buffer_read_offset -- streaming buffer read offset
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Description:
 The function <function>comedi_get_buffer_read_offset</function> is used on
 a subdevice that has a Comedi command in progress to get the current read
 position in the streaming buffer as an offset in bytes from the start of
 the buffer.  The position will wrap around to 0 when it reaches the buffer
 size.  This offset is only useful for memory mapped buffers.

 This function replaces <function><link
 linkend="func-ref-comedi-get-buffer-offset">comedi_get_buffer_offset</link></function> and has the same functionality.
Returns:
 On success, <function>comedi_get_buffer_read_offset</function> returns the current
 read position as an offset in bytes from the start of the buffer.
 On failure, <literal>-1</literal> is returned.

Function: comedi_get_buffer_write_offset -- streaming buffer write offset
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Description:
 The function <function>comedi_get_buffer_write_offset</function> is used on
 a subdevice that has a Comedi command in progress to get the current write
 position in the streaming buffer as an offset in bytes from the start of
 the buffer.  The position will wrap around to 0 when it reaches the buffer
 size.  This offset is only useful for memory mapped buffers.
Returns:
 On success, <function>comedi_get_buffer_write_offset</function> returns the
 current write position as an offset in bytes from the start of the buffer.
 On failure, <literal>-1</literal> is returned.

Function: comedi_get_buffer_read_count -- streaming buffer read count
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Param: unsigned int * read_count
Description:
 The function <function>comedi_get_buffer_read_count</function> is used on
 a subdevice that has a Comedi command in progress to get the number of bytes
 that have been read from the buffer, modulo
 <constant class="limit">UINT_MAX</constant> + <literal>1</literal>.  The
 value is stored in
 <code>*<parameter class="function">read_count</parameter></code>.
Returns:
 On success, <literal>0</literal> is returned.
 On failure, <literal>-1</literal> is returned.

Function: comedi_get_buffer_write_count -- streaming buffer write count
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Param: unsigned int * write_count
Description:
 The function <function>comedi_get_buffer_write_count</function> is used on
 a subdevice that has a Comedi command in progress to get the number of bytes
 that have been written to the buffer, modulo
 <constant class="limit">UINT_MAX</constant> + <literal>1</literal>.  The
 value is stored in
 <code>*<parameter class="function">write_count</parameter></code>.
Returns:
 On success, <literal>0</literal> is returned.
 On failure, <literal>-1</literal> is returned.

Function: comedi_get_buffer_size -- streaming buffer size of subdevice
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Description:
 The function <function>comedi_get_buffer_size</function> returns the size (in bytes)
 of the streaming buffer for the subdevice specified by
 <parameter class="function">device</parameter> and
 <parameter class="function">subdevice</parameter>.
Returns:
 On success, <function>comedi_get_buffer_size</function> returns the size of
 the buffer in bytes.
 On failure, <literal>-1</literal> is returned.

Function: comedi_get_cmd_generic_timed -- streaming input/output capabilities
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Param: comedi_cmd * command
Param: unsigned int chanlist_len
Param: unsigned int scan_period_ns
Description:
 The command capabilities of the subdevice indicated by the parameters
 <parameter class="function">device</parameter> and <parameter
 class="function">subdevice</parameter>
 are probed, and the results placed in the
 command structure pointed to by the parameter <parameter
 class="function">command</parameter>.
 The command structure pointed to by <parameter class="function">command</parameter>
 is modified to be a
 valid command that can be used as a parameter to
 <function><link linkend="func-ref-comedi-command">comedi_command</link></function>
 (after the command has additionally been assigned a valid
 <structfield>chanlist</structfield> array).
 The command measures scans consisting of <parameter class="function">chanlist_len</parameter>
 channels
 at a scan rate that corresponds to a period of
 <parameter class="function">scan_period_ns</parameter> nanoseconds.
 The rate is adjusted to a rate that the device
 can handle.
Returns:
 On success, <literal>0</literal> is returned.
 On failure, <literal>-1</literal> is returned.

Function: comedi_get_cmd_src_mask -- streaming input/output capabilities
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Param: comedi_cmd * command
Description:
 The command capabilities of the subdevice indicated by the parameters
 <parameter class="function">device</parameter> and <parameter
 class="function">subdevice</parameter>
 are probed, and the results placed in the
 command structure pointed to by <parameter class="function">command</parameter>.  The trigger
 source elements of the command structure are set to be the bitwise-or
 of the subdevice's supported trigger sources.  Other elements in the structure
 are undefined.
Returns:
 On success, <literal>0</literal> is returned.
 On failure, <literal>-1</literal> is returned.

Function: comedi_get_max_buffer_size -- maximum streaming buffer size
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Description:
 The function <function>comedi_get_max_buffer_size</function> returns the maximum
 allowable size (in bytes) of the streaming buffer for the subdevice
 specified by <parameter class="function">device</parameter>
 and <parameter class="function">subdevice</parameter>.
 Changing the maximum buffer
 size can be accomplished with
 <function><link
 linkend="func-ref-comedi-set-max-buffer-size">comedi_set_max_buffer_size</link></function>
 or with the <command>comedi_config</command> program,
 and requires appropriate privileges.
Returns:
 On success, the maximum allowable size (in bytes) of the streaming buffer
 is returned.
 On failure, <literal>-1</literal> is returned.

Function: comedi_get_read_subdevice -- find streaming input subdevice
Retval: int
Param: comedi_t * device
Description:
 The function <function>comedi_get_read_subdevice</function> returns the
 index of the subdevice
 whose streaming input buffer is currently accessible through the
 device <parameter class="function">device</parameter>, if there is one.
Returns:
 On success, <function>comedi_get_read_subdevice</function>returns the index
 of the current <quote>read</quote> subdevice if there is one,
 or <literal>-1</literal> if there is no <quote>read</quote> subdevice.
 On failure, <literal>-1</literal> is returned.

Function: comedi_get_write_subdevice -- find streaming output subdevice
Retval: int
Param: comedi_t * device
Description:
 The function <function>comedi_get_write_subdevice</function> returns the
 index of the subdevice
 whose streaming output buffer is currently accessible through the
 device <parameter class="device">device</parameter>, if there is one.
Returns:
 On success, <function>comedi_get_write_subdevice</function>returns the index
 of the current <quote>write</quote> subdevice if there is one,
 or <literal>-1</literal> if there is no <quote>write</quote> subdevice.
 On failure, <literal>-1</literal> is returned.

Function: comedi_mark_buffer_read -- streaming buffer control
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Param: unsigned int num_bytes
Description:
 The function <function>comedi_mark_buffer_read</function> is used on a subdevice
 that has a Comedi input command in progress.  It should only be used
 if you are using a <function>mmap</function> mapping to read data from Comedi's buffer
 (as opposed to calling <function>read</function> on the device file
 descriptor),
 since Comedi will automatically keep track of how many bytes have been
 transferred via <function>read</function> calls.  This function is
 used to indicate that the next <parameter class="function">num_bytes</parameter>
 bytes in the buffer
 are no longer needed and may be discarded.
Returns:
 On success, <function>comedi_mark_buffer_read</function> returns the
 number of bytes successfully marked as read.  The return value may be less than
 the <parameter class="function">num_bytes</parameter>.
 On failure, <literal>-1</literal> is returned.

Function: comedi_mark_buffer_written -- streaming buffer control
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Param: unsigned int num_bytes
Description:
 The function <function>comedi_mark_buffer_written</function> is used on a subdevice
 that has a Comedi output command in progress.  It should only be used
 if you are using a <function>mmap</function> mapping to write data to Comedi's buffer
 (as opposed to calling <function>write</function> on the device
 file descriptor), since Comedi
 will automatically keep track of how many bytes have been
 transferred via <function>write</function> calls.  This function is
 used to indicate that the next <parameter class="function">num_bytes</parameter>
 bytes in the buffer
 are valid and may be sent to the device.
Returns:
 On success, <function>comedi_mark_buffer_written</function> returns the
 number of bytes successfully marked as written.  The return value may be less than
 the <parameter class="function">num_bytes</parameter>.
 On failure, <literal>-1</literal> is returned.

Function: comedi_poll -- force updating of streaming buffer
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Description:
 The function <function>comedi_poll</function> is used on a subdevice that has a
 Comedi command in progress in order to update the streaming buffer.
 If supported by the driver, all available samples are copied to
 the streaming buffer.  These samples may be pending in DMA buffers
 or device FIFOs.
 Only a few Comedi drivers support this operation.
Returns:
 On success, <function>comedi_poll</function> returns the number of additional
 bytes available.
 On failure, <literal>-1</literal> is returned.

Function: comedi_set_buffer_size -- streaming buffer size of subdevice
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Param: unsigned int size
Description:
 The function <function>comedi_set_buffer_size</function> changes the size of the
 streaming buffer for the subdevice specified by
 <parameter class="function">device</parameter> and <parameter
 class="function">subdevice</parameter>.
 The buffer size will be set to <parameter class="function">size</parameter> bytes,
 rounded up to a multiple of the virtual memory page
 size.  The virtual memory page size can be determined using
 <code language="C">sysconf(_SC_PAGE_SIZE)</code>.

 This function does not require special privileges.  However,
 it is limited to a (adjustable) maximum buffer size, which can
 be changed by a privileged user calling
 <function><link
 linkend="func-ref-comedi-set-max-buffer-size">comedi_set_max_buffer_size</link></function>,
 or running the program <command>comedi_config</command>.
Returns:
 On success, <function>comedi_set_buffer_size</function> returns the new
 buffer size in bytes.
 On failure, <literal>-1</literal> is returned.

Function: comedi_set_max_buffer_size -- streaming maximum buffer size of subdevice
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Param: unsigned int max_size
Description:
 The function <function>comedi_set_max_buffer_size</function> changes the maximum
 allowable size (in bytes) of the streaming buffer for the subdevice
 specified by <parameter class="function">device</parameter> and
 <parameter class="function">subdevice</parameter>.  Changing the maximum buffer
 size requires the user to have appropriate privileges.
Returns:
 On success, <function>comedi_set_max_buffer_size</function> returns the new
 maximum buffer size in bytes.
 On failure, <literal>-1</literal> is returned.

Function: comedi_set_read_subdevice -- set streaming input subdevice
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Status: Works for Linux "in-tree" Comedi since kernel version 3.19.
Description:
 The function <function>comedi_set_read_subdevice</function> sets
 <parameter class="function">subdevice</parameter> as the current
 <quote>read</quote> subdevice if the subdevice supports streaming
 input commands.

 No action is performed if <parameter class="function">subdevice</parameter>
 is already the current <quote>read</quote> subdevice.

 Changes are local to the <emphasis>open file description</emphasis> for this
 <parameter class="function">device</parameter> and have no effect on other
 open file descriptions for the underlying device node.
Returns:
 On success, <literal>0</literal> is returned.
 On failure, <literal>-1</literal> is returned.

Function: comedi_set_write_subdevice -- set streaming output subdevice
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Status: Works for Linux "in-tree" Comedi since kernel version 3.19.
Description:
 The function <function>comedi_set_write_subdevice</function> sets
 <parameter class="function">subdevice</parameter> as the current
 <quote>write</quote> subdevice if the subdevice supports streaming
 output commands.

 No action is performed if <parameter class="function">subdevice</parameter>
 is already the current <quote>write</quote> subdevice.

 Changes are local to the <emphasis>open file description</emphasis> for this
 <parameter class="function">device</parameter> and have no effect on other
 open file descriptions for the underlying device node.
Returns:
 On success, <literal>0</literal> is returned.
 On failure, <literal>-1</literal> is returned.