IMiniportWaveCyclicStream::GetPosition

The GetPosition method gets the current position of the stream.

NTSTATUS 
  GetPosition(
    OUT PULONG  Position
    );

Parameters

Position

Output pointer for the position value. This parameter points to a caller-allocated variable into which the method writes the current byte position of the stream.

Return Value

GetPosition returns STATUS_SUCCESS if the call was successful. Otherwise, the method returns an appropriate error code.

Headers

Declared in portcls.h. Include portcls.h.

Comments

GetPosition outputs the stream's current play or record position. The position is expressed as a byte offset from the beginning of the DMA buffer and represents the miniport driver's best estimate of the byte position of the data currently in the DAC or ADC.

The position is zero immediately following initialization of the stream. A transition to the KSSTATE_STOP state (see KSSTATE) resets the position to zero. When the stream is halted by a transition from KSSTATE_RUN to KSSTATE_PAUSE or KSSTATE_ACQUIRE, the position freezes. It unfreezes when the stream transitions from KSSTATE_PAUSE or KSSTATE_ACQUIRE back to KSSTATE_RUN.

Audio hardware that internally buffers a portion of a playback or capture stream might make a precise position reading more difficult to obtain. In this case, the driver should estimate the current position as accurately as possible. For example, if an audio device prefetches the playback stream into an internal buffer, the driver might need to take both the buffer size and timing information into account in order to properly estimate the play position.

The GetPosition method is called at IRQL <= DISPATCH_LEVEL.

See Also

KSSTATE