Power Condition Timers - Western Digital Ultrastar DC HC310 Specifications

9.19.2

Power Condition Timers

The device has manufacturer specified power-on default settings for the power condition timers. Power condition
timers are changeable with the SET FEATURES Extended Power Conditions subcommand.
A power condition timer set to zero indicates that the associated power condition is disabled.
If the power condition is enabled, then the value of each timer specifies the time after command completion that the
device waits before transitioning to the power condition. All enabled power condition timers run concurrently.
On command completion all timers that were stopped are initialized with the Current Timer settings values and
started.
As a result of processing any command, the device may change to a different power condition.
If an enabled timer associated with a power condition lower than the power condition that the device is currently in
expires, then the device transitions to the power condition associated with that timer (e.g., if the standby_z timer is
set to a smaller interval than the idle_b timer, and the device is currently in the standby_z power condition, then the
device remains in the Standby_z power condition when the idle_b timer expires). If the timer expiration qualifies the
device to transition to more than one enabled power condition, then the device transitions to the power condition with
the least power consumption.
If a command is accepted that requires a transition to Active, then the timers are stopped. If a command is accepted
that does not require a transition to Active (e.g., a CHECK POWER MODE command), then the timers continues to
run.
Prior to entering into any power condition that prevents accessing the media (e.g., before a hard drive stops its
spindle motor during transition to the standby_z power condition) and if volatile write cache is enabled, then the
device shall write all cached data to the medium for the device (e.g., as a device does in response to a flush
command).
9.19.3 Interaction with Resets, Commands and other Features
On successful processing of a power cycle, the EPC enables sub command, the device:
When EPC is Enabling, the following content is executed.
1) stop all EPC timers.
2) copy the Saved Timer Enabled field to the Current Timer Enabled field, for all supported power conditions.
3) copy the Saved Timer Settings field to the Current Timer Settings field, for all supported power conditions.
4) initialize and restart all enabled EPC timers with Current values.
On successful processing of a hardware reset, a software reset, or a DEVICE RESET command, the device:
When EPC is Enabling, the following content is executed.
1) stop all EPC timers.
2) remain in the current power condition.
3) initialize and restart all enabled EPC timers with Current values.
The Extended Power Conditions feature set and the Advanced Power Management feature set are mutually
exclusive. All EPC subcommands, except Enable the EPC feature set, returns command aborted if the EPC feature
set is disabled. If the device processes a SET FEATURES Enable APM subcommand without error and IDENTIFY
DEVICE data word 120 bit 7 is set to one, then the device shall disable the EPC feature set.
During background activities, all EPC timers are stopped. On completion of the activity, any stopped EPC timers be continued
from w here they w ere paused.
Western Digital Hard Disk Drive OEM Specification
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