VLTRANSFER(3dm)						       VLTRANSFER(3dm)

NAME    [Toc]    [Back]

     vlBeginTransfer, vlEndTransfer, vlGetTransferSize - begin and end
     transfer on video path

SYNOPSIS    [Toc]    [Back]

     #include <dmedia/vl.h>

     int vlBeginTransfer(VLServer svr, VLPath path, int	count,
		   VLTransferDescriptor	*xferDesc);
     int vlEndTransfer(VLServer	svr, VLPath path);
     int vlGetTransferSize(VLServer svr, VLPath	path);

PARAMETERS    [Toc]    [Back]

     svr       Specifies the video server.

     path      Specifies the path.

     count     Specifies the number of transfer	descriptors in the array
	       passed. If count	= 0 then the continuous	mode transfer
	       operations are used.  Transfers will continue using ring
	       buffers,	if necessary,  until vlEndTransfer is called.

     xferDesc  If count	is non-zero, then xferDesc is an array of transfer
	       descriptors.  Each element of the array can specify a discrete,
	       continuous, or automatic	transfer. The contents of a descriptor
	       are described below.

DESCRIPTION    [Toc]    [Back]

     vlBeginTransfer immediately begins	a continuous transfer of video data on
     the specified path	if count is set	to zero.  If count is non-zero,	then
     vlBeginTransfer initiates a series	of transfers on	the specified path
     using the fields of each descriptor as follows.

     trigger An	event to trigger the transfer on.  VLTriggerImmediate means
	     that the transfer will start as soon as the daemon	is able	to
	     start.  VLDeviceEvent is generally	used to	indicate an external
	     triggering	mechanism, such	as the GPI input.

     delay   A count of	frames to wait after the trigger is received. In the
	     case of VLTriggerImmediate,
	     this may be ignored.

     count   The count of frames to transfer.

     mode    There are three current values for	the mode:

	     VL_TRANSFER_MODE_DISCRETE
		  means	that a single transfer of count	frames is executed.

	     VL_TRANSFER_MODE_CONTINUOUS
		  means	that a single transfer of undetermined length is
		  started, and will not	end until vlEndTransfer	is called.



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VLTRANSFER(3dm)						       VLTRANSFER(3dm)



	     VL_TRANSFER_MODE_AUTOTRIGGER
		  means	that every trigger received will cause a transfer of
		  count	frames.	 In this case if delay plus count is greater
		  than the time	between	triggers, undetermined behavior	may
		  result.

     The following events may be delivered once	vlBeginTransfer	has been
     called:

	  VLTransferComplete
	       events are delivered for	each frame transfer on paths which use
	       buffers.

	  VLTransferFailed
	       events are delivered to indicate	an error condition preventing
	       data transfer.

     vlEndTransfer ends	the transfer of	video data on the specified path.

     vlGetTransferSize returns the number of bytes of space required for a
     transfer on the server specified, using the path specified, for one frame
     or	field of data. For this	information to be useful, all controls that
     can effect	the size of the	data should be set before this call.

     The user is responsible for multiplying the returned value	by the number
     of	frames to get the buffer's size.

     There are several controls	that affect the	transfer of data.  See the
     documentation for the particular controls of a device that	affect the
     data transfer, such as rate, addresses, field or frame mode, depth,
     format, sizes, etc.

RETURN VALUE    [Toc]    [Back]

     If	successful, vlBeginTransfer and	vlEndTransfer return zero.  A value of
     -1	indicates an error, and	vlGetErrno(3v) can be called to	return the
     error code.

SEE ALSO    [Toc]    [Back]

     vlCreateBuffer(3dm), vlRegisterBuffer(3dm)


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