Table: LOAD/UNLOAD Command Block
An Immediate (lMM) bit of zero indicates that the Drive will not return status until the LOADIUNLOAD operation has completed. An IMM bit of one indicates that the Drive will return status as soon as the execution of all previous immediate commands have been completed and the Command Descriptor Block of the LOADIUNLOAD command has been validated. Note that the LINK bit MUST be zero if the IMM bit is set.
A Retension (RET) bit of one indicates that the Drive will perform a retension pass before the load or unload operation is performed. Reten-sion means moving the tape one complete pas~ between EOT and BOT.
A Load bit of one indicates that the tape will be moved to BOT. The tape is logically loaded which means that the Drive is able to accept medium access commands. A Load bit of zero indicates that the tape is logically unloaded. The Drive will no longer accept media access commands.
An End Of Tape (EaT) of zero indicates that the tape will be positioned at BOT after the load/unload operation has been performed. A EOT bit of one indicates that the tape will be positioned at EOT after the load/-unload operation has been performed. This allows fast retensioning of the cartridge next time it is used.
11-2 SCSI-2 Functional Specifications
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Combinations of the EOT, RET and Load bits are shown in the table below:EOT RET Load
I
Operation Performed0 0 0 Unload, move to BOT
0 0 1 Load, move to BOT
0 1 0 Retension, Unload, move to BOT 0 1 1 Retension, Load, move to BOT
1 0 0 Unload, move to EOT
1 0 1 Illegal, CHECK CONDITION
1 1 0 Retension, Unload, move to EOT
1 1 1 Illegal, CHECK CONDITION
Table: LOAD/UNLOAD Operations
11.3. Exception Handling
If CHECK CONDITION status is returned for a LOADIUNLOAD com-mand with an IMM bit of one, the load or unload operation has not been performed.
See sections on Error Conditions For All Commands, Deferred Errors and Error Conditions For Media Access Commands.
If the LINK and IMM bits both are set, then the Drive will return CHECK CONDITION status. The Error Code will be set to E$STE_IFIC.
If an illegal combination of Load, EOT and RET bits is detected, the Drive returns CHECK CONDITION status. The Error Code will be set to E$STE_IFIC.
71-3
SCS-2FuncffonalSpecmcaffons
Tandberg Data Load/Unload
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71-4 SCSl-2 Functional Specifications
12.
LOCATE Physical Command
LOCATE Logical Command
Locate
12. 1. Command Description
The LOCATE command causes the Drive to position the tape to a speci-fied position in the data stream. Both physical and logical positions are supported.
The LOCATE Physical command will interpret the Block Address in the CDB as a special key or "bookmark". All blocks, filemarks and setmarks can be identified with such a key. This position key can be obtained with the use of the READ POSITION command. While writing (or reading), the READ POSITION command is typically executed every time the tape is at a position that the Host system might want to go back to at a later stage. The returned position key can then be stored and used later as an input to the LOCATE command. These values can be regarded as keys that are unique to any given physical position on the tape. It might, however, be several keys that will result in the same logical position, as some physical tape blocks do not have any logical contents (i.e. ECC blocks or Filler blocks). The physical position numbers must be obtained with the READ POSITION command, and must not be manipulated in any way by the Host system. The LOCATE command will then bring the tape back to the same position as it was when the READ POSITION command was executed.
The LOCATE Logical command does not need special keys to get to a certain logical position. The Block Address in the CDBwill for this command be interpreted as the logical block position, meaning the number of blocks seen on the SCSI-bus from BOT. If a tape contains filemarks or setmarks, they will not count as logical blocks. It is therefore not possible to issue a LOCATE Logical command to such a tapemark.
12-1 SCSl-2 Functional Specifications
BYTE
12.2. Command Descriptor Block
BIT 7 6 5 4 3 2 1
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Table: LOCATE Command Block
When the Block address Type (BT) bit is cleared, the Block Location field in the CDB will be the logical block identifier for the LOCATE operation. If the BT bit is set, the Block Location field in the CDB will be the physical block identifier.
A change partition (CP) bit of one indicates that a change to the partition specified in the Partition field is to occur prior to positioning to the physical block specified in the Block Location address field (a CP of one is only legal when the Drive is in QFA mode). A CP bit of zero indicates that no partition change is to be made and the Partition field is to be ignored.
An immediate (IMM) bit of zero indicates that the Drive will not return status until the locate operation has completed. An IMM bit of one indi-cates that the Drive will return status as soon as the execution of all previous commands have been completed and the command descriptor block of the LOCATE command has been validated. If CHECK CONDI-TION status is returned for the LOCATE command with the IMM bit set to one, the locate operation will not be performed.
Block Location The input to the LOCATE command can be either physical or logical block id,ntifiers. After a successful command execution, the logical tape position will be located before the specified block (beginning.-of-media side).
12-2 SCSI-2 Functional Specifications
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Partition If the CP bit is one, the Partition field specifies the partition number into which to locate.The Drive has two valid partitions: