Seagate SCSI Interface Product Manual page 119

SCSI Interface Product Manual, Rev. J
Table 71: Log Parameters
Bit 7
Byte
0 (MSB)
1
2 DU [2]
3 Parameter Length (n-3 bytes) [8]
4
– –
:
– –
n
Notes.
[1] The Parameter Code field identifies the specific parameter that is being transferred with the Log Page.
These codes are listed and explained in the individual page code descriptions following Table 73.
Byte 2 is referred to as the Parameter Control byte. The meanings of the various fields are discussed in
notes [2] through [7]. For a Log Select command, these bits perform a control function, but on a Log
Sense command, they only report the drive settings of these bits in this same format on the Data In part of
the Log Sense command.
[2] Disable Update (DU). For the Log Select command, this applies only to the cumulative log parameter val-
ues (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 Unit 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 saving for
that log parameter. The drive saves the current cumulative and the current threshold parameter 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.
6 5
DS [3] TSD [4]
4 3
Parameter Code [1]
ETC [5] TMC [6]
Parameter Value [9]
2 1
(LSB)
Reserved LP [7]
105
0
– –
– –