IBM Ultrastar 36LZX, Specifications

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10.1.18 QUEUE TAG MESSAGES (20h, 21h, 22h)
Queue Tag XXh 1
Ordered Queue Tag message 22H
Head of Queue Tag message 21H
Simple Queue Tag message 20H 0
Description Value Byte
Figure 177. Queue Tag Messages
Queue Tag messages are used to specify an identifier called a Queue Tag for an I/O process which
establish the I_T_L_Q nexus. The queue tag filed is an 8-bit unsigned integer assigned by the initiator
during an initial connection. The Queue Tag for every I/O process for each I_T_L nexus must be unique.
If the target receives a Queue Tag that is currently in use for the I_T_L nexus, it will respond as "Incor-
rect Initiator Response". A Queue Tag becomes available for reassignment when I/O process ends. The
numeric value of a Queue Tag has no effect on the order of execution.
Whenever an initiator connects to the target, the appropriate Queue Tag message must be sent imme-
diately following the Identify message and within the same MESSAGE OUT phase to establish the
I_T_L_Q nexus for the I/O process.
Whenever the target reconnects to an initiator to continue a tagged I/O process, the Simple Queue Tag
message is sent immediately following the Identify and within the same MESSAGE IN phase to revive
the I_T_L_Q nexus for the I/O process.
10.1.18.1 SIMPLE QUEUE TAG (20h)
The Simple Queue Tag Message specifies that the current I/O process be placed in the command
queue. The order of execution with respect to other I/O processes received with Simple Queue Tag
Messages is up to the discretion of the target. The target will send a Simple Queue Tag Messages
after reselection for I/O processes that were received with either Simple, Ordered, or Head of Queue
Tag messages.
10.1.18.2 HEAD OF QUEUE TAG (21h)
Commands with this tag should be inserted into the head of the queue. When a command is being exe-
cuted, this tagged command will be inserted to the head of queue to be executed after the command
being currently executed. The previous executed command will not be terminated by this tagged com-
mand. This tagged command will wait until the previous command is completed. If plural head-of-queue
tagged commands are received, those command will be executed in LIFO(Last in First out) order.
10.1.18.3 ORDERED QUEUE TAG (22h)
This tagged command is executed in the order received. All commands received before this command
should be executed before this command and all commands received after this commands should be
executed after this command.
Ultrastar 36LZX hard disk drive specifications
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