User Manual

SCSI Commands Reference Manual, Rev. J 306
www.seagate.com Parameters for direct access devices
5.2.2.2.2 Parameter control byte
5.2.2.2.2.1 Introduction
The DU bit, TSD bit, and FORMAT AND LINKING field are collectively referred to as the parameter control byte. These fields are
described in this subclause.
DU (Disable Update) bit
For cumulative log parameter values, indicated by the PC field (see table 74) of the LOG SELECT command and LOG SENSE command, the dis-
able update (DU) bit is defined as follows:
0 DU set to zero indicates that the device server shall update the log parameter value to reflect all events that should be noted by that
parameter; or
1 DU set to one indicates that the device server shall not update the log parameter value except in response to a LOG SELECT command
that specifies a new value for the parameter.
Note. When updating cumulative log parameter values, a device server may use volatile memory to hold these values until a LOG SELECT or
LOG SENSE command is received with an SP bit set to one or a vendor specific event occurs. As a result the updated cumulative log
parameter values may be lost if a power cycle occurs.
If the PC field (see table 74) indicates that threshold values or default values are being processed, the device server shall:
a) set the DU bit to zero, if a LOG SENSE command is being processed; and
b) ignore the DU bit, if a LOG SELECT command is being processed.
Regardless of the value in the PC field, the device server shall process ASCII format list log parameters (see 5.2.2.2.2.4) and binary
format list log parameters (see 5.2.2.2.2.5) by:
a) setting the DU bit to zero, if a LOG SENSE command is being processed; and
b) ignoring the DU bit, if a LOG SELECT command is being processed.
TSD (Target Save Disable) bit
0 A target save disable (TSD) bit set to zero indicates that the logical unit implicitly saves the log parameter at vendor specific intervals.
This implicit saving operation shall be done frequently enough to insure that the cumulative parameter values retain statistical signifi-
cance
(i.e., across power cycles).
1 A TSD bit set to one indicates that either the logical unit does not implicitly save the log parameter or implicit saving of the log parame-
ter has been disabled individually by an application client setting the TSD bit to one. An application client may disable the implicit sav-
ing for all log parameters without changing any TSD bits using the GLTSD bit in the Control mode page. (see 5.3.12).
FORMAT AND LINKING field
The FORMAT AND LINKING field (see table 268) indicates the type of log parameter.
Table 268 FORMAT AND LINKING field
Code Log parameter type Reference
00b
Bounded data counter 5.2.2.2.2.2
01b
ASCII format list 5.2.2.2.2.4
10b
Bounded data counter or unbounded data counter 5.2.2.2.2.2 or 5.2.2.2.2.3
11b
Binary format list 5.2.2.2.2.5