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

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

Function: comedi_command_test -- test streaming input/output configuration
Retval: int
Param: comedi_t * device
Param: comedi_cmd * command
Description:
 The function comedi_command_test() tests the command structure pointed
 to by the parameter <parameter>command</parameter> and returns an
 integer describing the
 testing stages that were successfully passed.  In addition, if elements
 of the *<parameter>command</parameter> 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.

 The meanings of the return value are as follows:

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

Function: comedi_get_buffer_contents -- streaming buffer status
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Description:
 The function comedi_get_buffer_contents() is used on a subdevice
 that has a Comedi command in progress.  The number of bytes that
 are available in the streaming buffer is returned.  If there is
 an error, -1 is returned.

Function: comedi_get_buffer_offset -- streaming buffer status
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Description:
 The function comedi_get_buffer_offset() is used on a subdevice
 that has a Comedi command in progress.  This function returns
 the offset in bytes of the read pointer in the streaming buffer.
 This offset is only useful for memory mapped buffers.
 If there is an error, -1 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 comedi_get_buffer_size() returns the size (in bytes)
 of the streaming buffer for the subdevice specified by
 <parameter>device</parameter> and
 <parameter>subdevice</parameter>.  On error, -1 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>device</parameter> and <parameter>subdevice</parameter>
 are probed, and the results placed in the
 command structure pointed to by the parameter command.  The command
 structure *<parameter>command</parameter> is modified to be a
 valid command that can be used as a parameter to
 <link linkend="func-ref-comedi-command"><function>comedi_command</function></link>
 (after the command has additionally been assigned a valid chanlist array).
 The command measures scans consisting of <parameter>chanlist_len</parameter>
 channels
 at a scan rate that corresponds to a period of
 <parameter>scan_period_ns</parameter> nanoseconds.
 The rate is adjusted to a rate that the device
 can handle.
Returns:
 If successful, 0 is returned, otherwise -1.

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>device</parameter> and <parameter>subdevice</parameter>
 are probed, and the results placed in the
 command structure *<parameter>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:
 If successful, 0 is returned, otherwise -1.

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

Function: comedi_get_read_subdevice -- find streaming input subdevice
Retval: int
Param: comedi_t * device
Description:
 The function comedi_get_read_subdevice() returns the subdevice
 whose streaming input buffer is accessible through the
 device <parameter>dev</parameter>.  If
 there is no such subdevice, -1 is returned.

Function: comedi_get_write_subdevice -- find streaming output subdevice
Retval: int
Param: comedi_t * device
Description:
 The function comedi_get_write_subdevice() returns the subdevice
 whose streaming output buffer is accessible through the
 device <parameter>dev</parameter>.  If there is no such subdevice,
 -1 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 comedi_mark_buffer_read() is used on a subdevice
 that has a Comedi input command in progress.  It should only be used
 if you are using a mmap() to read data from Comedi's buffer
 (as opposed to calling read() on the device file),
 since Comedi will automatically keep track of how many bytes have been
 transferred via read() calls.  This function is
 used to indicate that the next <parameter>num_bytes</parameter>
 bytes in the buffer
 are no longer needed and may be discarded.
Returns:
 The function <function>comedi_mark_buffer_read</function> returns the
 number of bytes successfully marked as read,
 or -1 on error.  The return value may be less than
 <parameter>num_bytes</parameter> if you attempt to mark more
 bytes read than are currently available for reading, or
 if <parameter>num_bytes</parameter> must be rounded down
 to be an exact multiple of the subdevice's
 sample size (either sizeof(sampl_t) or sizeof(lsampl_t)).

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 comedi_mark_buffer_written() is used on a subdevice
 that has a Comedi output command in progress.  It should only be used
 if you are using a mmap() to write data to Comedi's buffer
 (as opposed to calling write() on the device
 file), since Comedi
 will automatically keep track of how many bytes have been
 transferred via write() calls.  This function is
 used to indicate that the next <parameter>num_bytes</parameter>
 bytes in the buffer
 are valid and may be sent to the device.
Returns:
 The function <function>comedi_mark_buffer_written</function> returns
 number of bytes successfully marked as written,
 or -1 on error.  The return value may be less than
 <parameter>num_bytes</parameter> if you attempt to mark more
 bytes written than the amount of free space currently available
 in the output buffer, or
 if <parameter>num_bytes</parameter> must be
 rounded down to be an exact multiple of the subdevice's
 sample size (either sizeof(sampl_t) or sizeof(lsampl_t)).

Function: comedi_poll -- force updating of streaming buffer
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Description:
 The function comedi_poll() 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.  If successful, the number of additional bytes
 available is returned.  If there is an error, -1 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 comedi_set_buffer_size() changes the size of the
 streaming buffer for the subdevice specified by
 <parameter>device</parameter> and <parameter>subdevice</parameter>.
 The buffer size will be set to <parameter>size</parameter> bytes,
 rounded up to a multiple of the virtual memory page
 size.  The virtual memory page size can be determined using
 sysconf(_SC_PAGE_SIZE).

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

Function: comedi_set_max_buffer_size -- streaming buffer size of subdevice
Retval: int
Param: comedi_t * device
Param: unsigned int subdevice
Param: unsigned int max_size
Description:
 The function comedi_set_max_buffer_size() changes the maximum
 allowable size (in bytes) of the streaming buffer for the subdevice
 specified by device and subdevice.  Changing the maximum buffer
 size requires the user to have appropriate privileges.
Returns:
 The old buffer size is returned on success.  On error, -1 is returned.