• 5.10.1. DX_IOTT Overview
• 5.10.2. DX_IOTT Definition
• 5.10.3. DX_IOTT Parameters
• 5.10.4. DX_IOTT Playback Array Example

5.10. DX_IOTT: Input/Output Transfer Table

The DX_IOTT data structure contains parameters for the Input/Output Transfer Table.

5.10.1. DX_IOTT Overview

The DX_IOTT structure identifies a source or destination for voice data. It is used with the dx_play( ) and dx_rec( ) functions.

A DX_IOTT structure describes a single data transfer to or from one file, memory block, or custom device. If the voice data is stored on a custom device, the device must have a standard Windows device interface. The device must support open( ), close( ), read( ), and write( ) and lseek( ).

To use multiple combinations, each source or destination of I/O is specified as one element in an array of DX_IOTT structures. The last DX_IOTT entry must have IO_EOT specified in the io_type field.

NOTE:

The DX_IOTT data area must remain in scope for the duration of the function if running asynchronously.

5.10.2. DX_IOTT Definition

The typedef for the structure is as follows:

    typedef struct dx_iott {

       unsigned short io_type;          /* Transfer type */

       unsigned short rfu;              /* Reserved */

       int              io_fhandle;     /* File descriptor */

       char *           io_bufp;        /* Pointer to base memory */

       unsigned long    io_offset;      /* File/Buffer offset */

       long int         io_length;      /* Length of data */

       DX_IOTT          *io_nextp;      /* Ptr to next DX_IOTT if IO_LINK set */

       DX_IOTT          *io_prevp;      /* (Optional) Ptr to previous DX_IOTT */

    }DX_IOTT;




5.10.3. DX_IOTT Parameters

Parameter	Description
io_type	Specifies whether the data is stored in a file or in memory. It also determines if the next DX_IOTT structure is contiguous in memory, linked, or if this is the last DX_IOTT in the chain. It is also used to enable WAVE data offset I/O. Set the io_type field to an OR combination of the following defines.
	Data Transfer Type	Description
	IO_DEV	file data
	IO_MEM	memory data
	IO_UIO	nonstandard storage media data using the dx_setuio( ) function; must be ORed with IO_DEV
	Structure Linkage	Description
	IO_CONT	the next DX_IOTT structure is contiguous (default)
	IO_LINK	the next DX_IOTT structure is part of a linked list
	IO_EOT	this is the last DX_IOTT structure in the chain
	If none of IO_CONT, IO_LINK, or IO_EOT are specified, IO_CONT is assumed.
	Other Types	Description
	IO_USEOFFSET	enables use of the io_offset and io_length fields for WAVE data
	To enable offset I/O for WAVE data, set the DX_IOTT io_type field to IO_USEOFFSET ORed with the IO_DEV define (to indicate file data rather than memory buffer). NOTE: Wave files cannot be recorded to memory buffers or played from memory buffers.
io_fhandle	Specifies a unique file descriptor provided by the dx_fileopen( ) function if IO_DEV is set in io_type. If IO_DEV is not set in io_type, io_fhandle should be set to 0.
io_bufp	Specifies a base memory address if IO_MEM is set in io_type.
io_offset	Specifies one of the following:
	an offset from the beginning of a file if IO_DEV is specified in io_type.
	for WAVE file offset I/O (IO_DEV is ORed with IO_USEOFFSET in io_type), set the io_offset field to a file offset value that is calculated from the beginning of the WAVE audio data rather than the beginning of the file (that is, the first 80 bytes that make up the file header are not counted).
	an offset from the base buffer address specified in io_bufp if IO_MEM is specified in io_type.
io_length	Specifies the number of bytes allocated for recording or the byte length of the playback file. Specify -1 to play until end of data. During dx_play( ), a value of -1 causes playback to continue until an EOF is received or one of the terminating conditions is satisfied. During dx_rec( ), a value of -1 in io_length causes recording to continue until one of the terminating conditions is satisfied.
io_nextp	Points to the next DX_IOTT structure in the linked list if IO_LINK is set in io_type.
io_prevp	Points to the previous DX_IOTT structure. This field is automatically filled in when dx_rec( ) or dx_play( ) are called. The io_prevp field of the first DX_IOTT structure is set to NULL.

5.10.4. DX_IOTT Playback Array Example

The following example uses different sources for playback, an array or linked list of DX_IOTT structures.

#include <srllib.h>

#include <dxxxlib.h>

#include <windows.h>

DX_IOTT iott[3];

/* first iott: voice data in a file with descriptor fd1*/

iott[0].io_fhandle = fd1;

iott[0].io_offset = 0;

iott[0].io_length = -1;

iott[0].io_type = IO_DEV;

/* second iott: voice data in a file with descriptor fd2 */

iott[1].io_fhandle = fd2;

iott[1].io_offset = 0;

iott[1].io_length = -1;

iott[1].io_type = IO_DEV;

/* third iott: voice data in a file with descriptor fd3 */

iott[2].io_fhandle = fd3;

iott[2].io_offset = 0;

iott[2].io_length = -1;

iott[2].io_type = IO_DEV|IO_EOT;

      .

      .

/* play all three voice files: pass &iott[0] as argument to dx_play( )

      .

      .

/* form a linked list of iott[0] and iott[2] */

iott[0].io_nextp=&iott[2];

iott[0].io_type|=IO_LINK

/* pass &iott[0] as argument to dx_play( ). This time only files 1 and 3

 * will be played.

 */

    .

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