User Manual

SCSI Commands Reference Manual, Rev. J 423
www.seagate.com Parameters for direct access devices
PM_BG_PRECEDENCE field
The PM_BG_PRECEDENCE field (see table 398) specifies the interactions between background functions (see SPC-5) and power management.
The behavior of the idle and standby condition timers controlled by this mode page is defined in the power condition overview
and the power condition state machine (see SPC-5).
Table 398 PM_BG_PRECEDENCE field
Code Description
00b
Vendor specific
01b
Performing background functions take precedence over maintaining low power conditions as follows:
a) if the logical unit is in a low power condition as the result of a power condition timer associated with that condition expiring,
then:
1) the logical unit shall change from that power condition, if necessary, to the power condition required to perform the back-
ground function, when:
a) a timer associated with a background scan operation expires, and that function is enabled (see SBC-4);
or
b) an event occurs to initiate a device specific background function, and that function is enabled (see SPC-5);
2) the logical unit shall perform the background function(s) based on the definitions in this standard and other command stan-
dards (e.g., if the device server receives a command while performing a background function, then the logical unit shall sus-
pend the function to process the command);
3) if more than one condition is met to initiate a background function, then:
a) all initiated background functions shall be performed; and
b) the order of performing the functions is vendor specific; and
4) when all initiated background functions have been completed, the device server shall check to see if any power condition
timers have expired. If any power condition timer has expired, then the logical unit shall change to the power condition
associated with the highest priority timer that has expired;
or
b) if the logical unit is performing a background function, and a power condition timer expires, then the logical unit shall perform
all initiated background functions before the logical unit changes to a power condition associated with a timer has expired.
10b
Maintaining low power conditions take precedence over performing background functions as follows:
a) if the logical unit is in a low power condition, then the logical unit shall not change from that power condition to perform a
background function;
b) the device server may perform any initiated and enabled background function based on the definitions in this standard or
other command standards, if all of the following are true:
A) a condition is met to initiate a background function;
B) that background function is enabled;
C) the logical unit changes to a power condition in which the background function may be performed (e.g., the device server
processes a medium access command causing the logical unit to change its power condition to continue processing that
command); and
D) all outstanding application client requests have been completed;
or
c) if the logical unit is performing a background function, and a power condition timer expires that causes a change to a power
condition in which the logical unit is unable to continue performing the background function, then the logical unit shall:
A) suspend the background function; and
B) change to the power condition associated with the timer that expired.
11b
Reserved