settings.
Overriding the Power State Configuration for an Individual Device
The default Power Manager implementation maintains system-state-to-device-state mappings in the registry under the HKEY_LOCAL_MACHINESystemCurrentControlSetState key. Each system power state corresponds to a separate subkey and you can create additional subkeys for OEM-specific power states.
Table 3-19 shows a sample configuration for the system power state On. This configuration causes Power Manager to switch all devices, except the backlight driver BLK1: driver, into the D0 device power state. The backlight driver BLK1: can only go to the D2 state.
Table 3-19 Default and driver-specific power state definitions for system power state On
| Location | HKEY_LOCAL_MACHINESystemCurrentControlSetState On | ||
|---|---|---|---|
| Entry | Flags | Default | BKL1: |
| Type | REG_DWORD | REG_DWORD | REG_DWORD |
| Value | 0x00010000 (POWER_STATE_ON) | 0 (D0) | 2 (D2) |
| Description | Identifies the system power state associated with this registry key. For a list of possible flags, see the Pm.h header file in the PublicCommonSdkInc folder. | Sets the power state for drivers by default to the D0 state when the system power state is On. | Sets the backlight driver BLK1: to the D2 state when the system power state is On. |
Overriding the Power State Configuration for Device Classes
Defining device power state for multiple system power states individually can be a tedious task. Power Manager facilitates the configuration by supporting device classes based on IClass values, which can be used to define the power management rules. The following three default class definitions are found under the HKEY_LOCAL_MACHINESystemCurrentControlSetControlPowerInterfaces registry key.
¦ {A3292B7-920C-486b-B0E6-92A702A99B35} Generic power management-enabled devices.
¦ {8DD679CE-8AB4-43c8-A14A-EA4963FAA715} Power-management-enabled block devices.
¦ {98C5250D-C29A-4985-AE5F-AFE5367E5006} Power-management-enabled Network Driver Interface Specification (NDIS) miniport drivers.
Table 3-20 shows a sample configuration for the NDIS device class, which specifies that NDIS drivers only go as high as the D4 state.
Table 3-20 Sample power state definition for NDIS device class
| Location | HKEY_LOCAL_MACHINESystemCurrentControlSetControlPowerStateOn {98C5250D-C29A-4985-AE5F-AFE5367E5006} |
|---|---|
| Entry | Default |
| Type | REG_DWORD |
| Value | 4 (D4) |
| Description | Sets the device power state for NDIS drivers to the D4 state when the system power state is On. |
Processor Idle State
In addition to power-management-enabled applications and device drivers, the kernel also contributes to
