User Guide

Ampex 1308911-02 5-5

libdd2 API Functions DST API Overview

int adfn; /* Absolute double-frame number */

int ptid; /* Partition ID (starting at zero!) */

int fsn; /* File section number (within partition) */

dst_dbn_st ldbn; /* Logical data block number (within FSN) */

dst_dd2_pos_st;

valid Bit mask that indicates whether the position is valid and, if so, which

structure members contain valid information

#define DST_POSN_INVALID 0x0000

#define DST_ADFN_VALID 0x0001

#define DST_DBN_VALID 0x0002

#define DST_FSN_VALID 0x0004

#define DST_PTID_VALID 0x0008

#define DST_TIMECODE_VALID 0x0010

adfn

Absolute Double Frame Number - The number of the physical block

that contains the speciﬁed location. This is an optional value that,

strictly speaking, is not part of the position speciﬁcation. When used, it

provides a very accurate hint to the drive, expediting high-speed

positioning to the speciﬁed position.

DO NOT SPECIFY AN ADFN UNLESS YOU ARE CERTAIN THAT

IT IS ACCURATE. An incorrect

adfn can set the tape position to an

invalid location (such as past end of data).

ptid Partition Identiﬁcation Number (ID) - The number of the partition that

contains the speciﬁed location. Partitions are numbered sequentially on

the tape starting at zero.

fsn File Section Number - The number of the ﬁle section that contains the

speciﬁed location. Files are numbered sequentially within a partition

starting at one.

ldbn Logical Data Block Number - The block number of the location. Data

blocks are numbered sequentially within a ﬁle section starting at zero.

dst_600_pos_st Structure

This structure type represents position in DST600 format and may not be portable across

platforms. It is similar to the native DST structure, except that is identiﬁes the location by

cumulative data block number within the partition rather than logical data block number

within the ﬁle section. Use this position form only if you must maintain DST 600

compatibility.

typedef struct

{

u_int valid; /* Flag indicating which members are valid */