Motorola USB08 - Manual (Page 147)

Universal USB Device Driver (USBIO)
Architecture
USB08 Evaluation Board Designer Reference Manual
MOTOROLA Universal USB Device Driver (USBIO) 147
All registry entries describing device power states are DWORD
parameters where the value 0 corresponds to
DevicePowerD0 , 1 to
DevicePowerD1 , and so on.
The parameter PowerStateOnOpen specifies the power state to which
the device is set if the first file handle is opened. If the last file handle is
closed the USB device is set to the power state specified in the entry
PowerStateOnClose .
If at least one file handle is open for the device the key
MinPowerStateUsed describes the minimal device power state that is
required. If the value is set to 0 the computer will never go into a sleep
state. If this key is set to 2 the device can go into a suspend state but not
into D3 (Off). A power-down request caused by a low battery condition
cannot be suppressed by using this parameter.
If no file handle is currently open for the device, the key
MinPowerStateUnused defines the minimal power state the device
can go into. Thus, its meaning is similar to that of the parameter
MinPowerStateUsed .
If the parameter AbortPipesOnPowerDown is set to 1 all pending
requests submitted by the application are returned before the device
enters a sleeping state. This switch should be set to 1 if the parameter
MinPowerStateUsed is different from D0. The pending I/O requests
are returned with the error code USBIO_ERR_POWER_DOWN . This
signals to the application that the error was caused by a power down
event. The application may ignore this error and repeat the request. The
re-submitted requests will be queued by the USBIO driver. They will be
executed after the device is back in state D0.