Page
114
LTO SCSI Interface Manual
SPACE
The Space command uses three methods to move the tape. This command moves
the position:
•
Forward or backward a specified number of blocks.
•
Forward or backward a specified number of filemarks.
•
Forward to the end of recorded data (EOD).
If the target block or filemark is in the buffer of the drive, no tape motion results,
otherwise, spacing is done at high search speed.
Command Descriptor Block
Byte
Bits
7
6
5
4
3
2
1
0
0
Operation Code (11h)
1
Ignored LUN
Reserved
Code
2
Count, MSB
3
Count
4
Count, LSB
5
Control
Field Descriptions
Field
Bytes
Bits
Description
Operation
Code
0
The Operation Code for Space is 11h.
Ignored
Logical
Unit
1
5-7
The LUN field is residual from the SCSI-1 days and is ignored.
Code
1
0-2
000b = Move Count blocks
001b = Move Count filemarks
011 = Move to end of recorded data (EOD)
Count
2-4
This field specifies the number of blocks or filemarks to space over.
A positive Count moves the tape forward. A negative (2's comple-
ment) Count moves the tape backward. A zero Count causes no
media movement and is not an error. For Space to EOD operation,
this field is ignored.
Reserved
All reserved bits must be 0.
Control
5
See Control Byte Format on page 18.
The Space command instructs the drive to set a new logical position relative to the
current logical position. How this is done is dependent on the value of the Code field
and the Count field. The Count field is a signed value indicating the distance to
move, negative indicating movement towards BOT and positive indicating movement
towards EOT.
If the Code field is 000b, then the logical position is moved the number of blocks
indicated by the Count field. If a file mark is detected between the current logical
position and the requested logical position, the new logical position is set to
immediately after the file mark in the direction of the space operation. If BOT or EOD
is detected before the requested logical position, then the logical position is set to
that position.
