HasExternalPower Property

Article
09/21/2010

The HasExternalPower property gets or sets whether the device currently has external power. This property is used only for devices that can be self-powered.

This property is read/write.

Syntax

HRESULT put_HasExternalPower(
  [in]           VARIANT_BOOL fvarHasExternalPower
);

HRESULT get_HasExternalPower(
  [out, retval]  VARIANT_BOOL *pfvarHasExternalPower
);

Property Value

The new value for the device.

Error Codes

HasExternalPower returns S_OK if the operation succeeds or E_POINTER if the *pHasExternalPower parameter is not a valid pointer.

Remarks

The HasExternalPower property is used only for devices that can be self-powered and is used to determine the value of the D0 bit that is returned from a GET_STATUS request sent that is to the device, as described in section 9.4.5 of the USB 2.0 specification.

The following C++ code example how to set and get the HasExternalPower property.

HRESULT CLoopBackDevice::UpdateHasExternalPower(ISoftUSBDevice *piDevice)
{
HRESULT hr = S_OK;
VARIANT_BOOL   fHasExternalPower = FALSE;
VARIANT_BOOL   fNewHasExternalPower = FALSE;
 
 
//Get the current HasExternalPower state
hr = piDevice->get_HasExternalPower (&fHasExternalPower);
if(FAILED(hr))
 goto Exit;
 
//Update HasExternalPower if required
if (fNewHasExternalPower != fHasExternalPower)
{
hr = piDevice->put_HasExternalPower (fNewHasExternalPower);
if(FAILED(hr))
 goto Exit;
}
Exit:
return hr;
}

Requirements

Header

SoftUSBif.h

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