WODM_PREPARE

See also WODM_UNPREPARE

Sent to a waveform output device driver to request the driver to prepare a data block for playback. If data blocks are accessed at interrupt time, they must be page locked to ensure that the memory is not swapped out to disk.

The return value is an error code, or zero (MMSYSERR_NOERROR) if the operation is successful. Possible error codes are:

MMSYSERR_NOTENABLED	The driver failed to load or initialize.
MMSYSERR_NOTSUPPORTED	The driver does not support this message.

DWORD dwParam1

Specifies a far pointer to WAVEHDR structure identifying the data block.

DWORD dwParam2

Specifies the size of the WAVEHDR structure.

Driver support for this message is optional. If a driver supports this message, then it must also support WODM_UNPREPARE.

The default response for this message is to return MMSYSERR_NOTSUPPORTED. In this case, MMSYSTEM will page lock the memory for the driver. If a driver requires other operations to prepare a data block for playback, it should set the WHDR_PREPARED bit in the dwFlags field of the WAVEHDR structure and return MMSYSERR_NOERROR. In this case, MMSYSTEM assumes the driver has prepared the data block and does not page lock the memory. If a data block has already been prepared, MMSYSERR_NOERROR should be returned.