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WIDM_PREPARE
 
        This message is sent to a waveform input device driver to
        request the driver to prepare a data block for input. If data
        blocks are accessed at interrupt time, they must be page locked
        to ensure that the memory is not swapped out to disk.
 
Parameters
        DWORD dwParam1
            Specifies a far pointer to WAVEHDR structure identifying
            the data block.
 
        DWORD dwParam2
            Specifies the size of the WAVEHDR structure.
 
Return value
        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.
 
Comments
        Driver support for this message is optional. If a driver
        supports this message, then it must also support WIDM_UNPREPARE.
 
        The default response for this message is to do nothing but
        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.
 
See also
        WIDM_UNPREPARE
 
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