Fujitsu MBA3073 SERIES Technical Manual page 165

(2) Pointer operation
When the TARG issues a request message or executes reconnection, the INIT saves the pointer
(that is, the INIT sets the current pointer value to the Saved pointer) or restores the pointer (that is,
the INIT sets the Saved pointer value to the current pointer).
Within the Saved pointer, the command pointer and status pointer always have their initial value
of that command. The command pointer points to the first byte position of the CDB (command),
and the status pointer points to the storage position of status byte in that command. While in the
Saved pointer, the data pointer points to the beginning of data area of the command when the
command execution has started. These values are held until the TARG issues a SAVE DATA
POINTER message to the INIT. When the INIT receives this SAVE DATA POINTER message,
the INIT stores the current data pointer value in the saved data pointer area.
The TARG can restore the pointers by sending the RESTORE POINTERS message to the INIT.
When the INIT receives this RESTORE POINTERS message, it stores pointer values of the saved
pointer in the corresponding current pointer.
If the INIT receives an IDENTIFY message after the RESELECTION phase, the INIT restores the
pointers in the similar way as when it has received the RESTORE POINTERS message.
If a command is in the disconnect state, the INIT saves only the saved pointer value of the
command. Therefore, if the command disconnect is expected during data transfer, the TARG
shall save the current data pointer values by issuing the SAVE DATA POINTER message before
issuing the DISCONNECT message.
Note:
As the TARG may set any pointer value before starting disconnect processing or command
termination, the pointer value of the INIT may or may not point to the byte position of the data
recently transferred over the SCSI bus.
Figure 2.2 shows the SCSI pointer configuration. It indicates the execution of the command
(CDB ) after the INIT was connected with TARG#0 and LUN#0. Therefore, the current pointer
0
keeps each pointer value to execute the command (CDB
data, and status pointers for this command are X
The current pointer values are updated to (X
and executing the data transfer. The saved pointer values except for the data pointer keep the
initial values (X , Z
0
initial value at the command issuance, (Y
saving operation was performed by the TARG specification, (Y
values can be restored into the current pointer by a RESTORE POINTERS message when the
TARG retries the command.
Also, the pointers to the commands (CDB
are stored at the corresponding positions (1, m) in the saved pointer group. They are fetched and
restored as the current pointers when the commands are reconnected.
158
0
) until the command execution ends. The saved data pointer value keeps the
0
), or the current pointer value at the time the pointer
0
, CDB
1
). The initial values for the command,
0
, Y , and Z .
0 0 0
+ c) and (Y + d) by fetching the command (CDB
0
+ dn). These saved pointer
0
) which are in operation with other logical units
m
)
0
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