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176
[2]
Disable Update (DU). For the LOG SELECT command, this applies only to the cumulative LOG PARAME-
TER values (indicated by 01 in the PC field of the LOG SELECT and LOG SENSE command descriptor
block). The drive can set this bit to one or zero also (see note [7] following).
The DU flag bit is defined as follows:
a. A zero value indicates that the drive shall update the LOG PARAMETER value to reflect all events that
should be logged by that parameter.
b. A one value indicates that the drive shall not update the LOG PARAMETER value except in response
to a LOG SELECT command that specifies a new value for the parameter.
The DU flag is set to one when the current cumulative value of the parameter counter it controls reaches
its maximum value (see note [8]). Upon reaching this maximum value, the data counter does not wrap
around and start over at zero. Incrementing of other counters within the same log pages ceases. Counters
do not restart automatically if the overflowed counter is re-initialized. If the data counter reaches its maxi-
mum value during the execution of a command, the drive completes the command. Drive counter updates
are performed in the background. This means a counter may overflow long after a command has com-
pleted, so the drive must treat this condition as a REUNIT ATTENTION with the additional sense code set
to Log Counter at max for all initiators if RLEC=1 (Report Log Exception Condition bit of the Control Mode
Page 0Ah).
Since the drive uses volatile memory to hold cumulative values, they will be lost when a power cycle
occurs. Unless the initiator commands the drive to save them to non-volatile memory using a LOG
SELECT or LOG SENSE command with the SP bit set to one.
The DU bit is not defined for threshold values (indicated by the PC field of the LOG SENSE command
descriptor block) nor for list parameters (indicated by the LP bit). The drive ignores the value of DU bits in
a LOG SELECT command applicable to threshold values or list parameters.
[3]
If Disable Save (DS) is zero, it indicates that the drive supports LOG SELECT and LOG SENSE data sav-
ing for that LOG PARAMETER. The drive saves the current cumulative and the current threshold parame-
ter values in response to a LOG SELECT or LOG SENSE command with an SP bit of one. A DS bit of one
indicates that the drive does not support saving that LOG PARAMETER in response to a LOG SELECT or
LOG SENSE command with a SP bit of one.
[4]
Target Save Disable (TSD). A zero indicates that the drive shall save frequently enough to insure statisti-
cal significance. The drive's method is to save after each thermal calibration, which is typically (may not
always be) once every ten minutes. A one bit indicates that the drive does not use its save method.
[5]
Enable Threshold Comparison (ETC). A one indicates that a comparison to the threshold value is per-
formed whenever the cumulative value is updated. A bit of zero indicates the comparison is not performed.
The value of the ETC bit is the same for both the threshold and cumulative parameters.
[6]
The Threshold Met Criteria (TMC) field defines the basis for comparison of the cumulative and threshold
values. See Table 112 for meanings of values in this field. The TMC field is only valid when the ETC bit is
one.
Table 112:
Threshold Met Criteria
Code
Basis for Comparison
00b
Notify of every update of cumulative value
01b*
Cumulative value equal to threshold value
10b*
Cumulative value not equal threshold value
11b*
Cumulative value greater than threshold value
*Comparison made at every update of cumulative value.
If the ETC bit is one* and the result of the comparison is true, a REUNIT ATTENTION Condition is gener-
ated for all initiators. When reporting the REUNIT ATTENTION Condition, the drive sets the sense key to
REUNIT ATTENTION, and the additional sense code to Threshold Condition Met.
*The RLEC bit (Report Log Exception Condition) in Mode page 0AH (Table 152) must also be one.
[7]
List Parameter (LP). Zero indicates the parameter is a data counter. One indicates that the parameter is a
list parameter. This bit only has meaning for the LOG SENSE command Data In pages.
SCSI Interface Product Manual, Rev. B
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