IMiniportWaveRTStreamNotification::AllocateBufferWithNotification method (portcls.h)

Article
10/21/2021

The AllocateAudioBufferWithNotification method allocates a cyclic buffer for audio data when you want to implement DMA-driven event notification. If you do not want event notification, you must use IMiniportWaveRTStream::AllocateAudioBuffer.

Syntax

NTSTATUS AllocateBufferWithNotification(
  [in]  ULONG               NotificationCount,
  [in]  ULONG               RequestedSize,
  [out] PMDL                *AudioBufferMdl,
  [out] ULONG               *ActualSize,
  [out] ULONG               *OffsetFromFirstPage,
  [out] MEMORY_CACHING_TYPE *CacheType
);

Parameters

[in] NotificationCount

Specifies the number of notifications wanted per buffer cycle. Valid values are 1 or 2, where 1 indicates a single notification at the end of the cyclic buffer and 2 indicates two notifications per buffer cycle, one at the mid-point of the buffer and one at the end.

[in] RequestedSize

Specifies the requested size, in bytes, of the audio buffer.

[out] AudioBufferMdl

Output pointer for a memory descriptor list (MDL) that describes the audio buffer. This parameter points to a caller-allocated pointer variable into which the method writes a pointer to the MDL.

[out] ActualSize

Output pointer for the actual size, in bytes, of the allocated buffer. This parameter points to a ULONG variable into which the method writes the size value.

[out] OffsetFromFirstPage

Output pointer for the offset (in bytes) of the buffer, from the start of the first page in the MDL. This parameter points to a caller-allocated ULONG variable into which the method writes the offset value.

[out] CacheType

Specifies the type of caching that the client requests for the audio buffer. This parameter is a MEMORY_CACHING_TYPE enumeration value

Return value

AllocateBufferWithNotification returns STATUS_SUCCESS if the call was successful. Otherwise, the method returns an appropriate error status code. The following table shows some of the possible error status codes.

Return code	Description
STATUS_UNSUCCESSFUL	The driver does not support the specified combination of buffer attributes.
STATUS_INSUFFICIENT_RESOURCES	There is insufficient memory available to allocate the buffer.
STATUS_DEVICE_NOT_READY	The device is not ready.

Remarks

Note Miniports for Intel High Definition Audio Codecs must specify a CacheType of MmWriteCombined to ensure cache coherency. This is because the Intel High Definition Audio Controller may be configured for non-snoop operation.

After receiving a KSPROPERTY_RTAUDIO_BUFFER_WITH_NOTIFICATION request from the client, the port driver calls the AllocateBufferWithNotification method to allocate a cyclic buffer that the port driver can later map to the virtual address space of the client. AllocateBufferWithNotification operates in a manner similar to IMiniportWaveRTStream::AllocateAudioBuffer. Additionally, AllocateBufferWithNotification identifies to the WaveRT port driver that DMA-driven event notification is wanted, and it specifies how many notifications per cycle of the cyclic buffer are needed.

Requirements

Requirement	Value
Minimum supported client	Available in Windows Vista and later Windows operating systems.
Target Platform	Universal
Header	portcls.h
IRQL	Passive level.