93
Western Digital Hard Disk Drive OEM Specification
9.19
Extended Power Conditions (EPC) Feature
The Extended Power Conditions feature set provides a host with additional methods to control the power condition of
a device.
Subcommand code 4Ah enables, disables, and configures the use of the Extended Power Conditions feature set. If
the EPC feature set is not supported, then the device return command aborted Table 73 describes the EPC
subcommands and Table 74 describes the power condition IDs.
EPC Subcommand
Description
0h
Restore Power Condition Settings
1h
Go To Power Condition
2h
Set Power Condition Timer
3h
Set Power Condition State
4h
Enable the EPC feature
5h
Disable the EPC feature
6h … Fh
Reserved
Table 73 Extended Power Conditions Subcommands
Power Condition ID Power Condition Name
Description
00h
standby_z
Standby
01h
standby_y
Low RPM Idle
02h…80h
Reserved
81h
idle_a
Active Idle
82h
idle_b
Low Power Idle
83h
idle_c
Low RPM Idle
84h … FEh
Reserved
FFh
All
All supported EPC power conditions
Table 74 Power Condition IDs
9.19.1
Power Conditions
i
dle_a,
i
dle_b and idle_c are power conditions within the PM1:Idle power management state. standby_y and
standby_z are power conditions within the PM2:Standby power management state. Please refer to ACS -
2 “3.1
Definitions and abbreviations” about PM1:Idle and PM2:Standby. The power conditions are ordered from highest
power consumption (i.e., shortest recovery time) to lowest power consumption (i.e., longest recovery time) as
follows:
idle_a power >= idle_b power >= idle_c power >= standby_y power >= standby_z power
Each of these power conditions has a set of current, saved and default settings. Default settings are not modifiable.
Default and saved settings persist across power cycles. The current settings do not persist across power cycles.
