Hitachi HUS151414VL3600, Specifications

Page: 240 / 321

Hitachi Ultrastar 15K147 SCSI Hard Disk Drive Specification
222
19.1.19 Queue Tag messages (20H, 21H, 22H)
Table 181:
Queue Tag messages
Queue Tag messages are used to specify an identifier called a Queue Tag for an I/O process that establishes the I_T_L_Q
nexus. The queue tag field 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 “Incorrect Initiator Response”. A Queue Tag becomes available for reassignment when the 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 immediately 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 message is sent immediately fol-
lowing the Identify and within the same MESSAGE IN phase to revive the I_T_L_Q nexus for the I/O process.
19.1.19.1 Simple (20h)
The Simple 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 messages is up to the discretion of the Target. The Target will send Simple
messages after reselection for I/O processes that were received with either Simple, Ordered, or Head of Queue messages.
19.1.19.2 Head Of Queue (21h)
Commands with this tag should be inserted into the head of the queue. When a command is being executed, this tagged com-
mand 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 command. This tagged command will wait until the previous command is com-
pleted. If plural head-of-queue tagged commands are received, those command will be executed in LIFO (Last in First out)
order. This will be ignored if the WCE bit is set.
19.1.19.3 Ordered (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.
19.1.20 Ignore Wide Residue
Table 182:
I gnore Wide Residue message format
The Ignore Wide Residue message is sent from the Target to indicate that the number of valid bytes sent during the last REQ/
ACK handshake of a DATA IN phase is less than the negotiated transfer width. The ignore field (always = 01h) indicates that
one byte (data bits 8-15) should be ignored. This message is sent immediately after the DATA IN phase and prior to any other
Byte Value Description
0 20H Simple Queue
21H Head of Queue
22H Ordered
1 XXh Queue Tag
Byte Value Description
0 23H Ignore Wide Residue message
1 01H Ignore