MIDM_ADDBUFFER

Sent to a MIDI input device driver to add a buffer to the input queue.

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.
MIDIERR_UNPREPARED	The specified data buffer has not been prepared for input.

DWORD dwParam1: Specifies a far pointer to a MIDIHDR data structure identifying the buffer.
DWORD dwParam2: Specifies the size of the MIDIHDR structure.

The driver should clear the MHDR_DONE bit and set the MHDR_INQUEUE bit in the header structure, and place the data block in its input queue. Then the driver should return control to the client by returning MMSYSERR_NOERROR.

Input to the buffer should occur as an interrupt-driven process. Only system-exclusive data should be placed in the buffer. Other MIDI events should be sent directly to the client application by sending a MIM_DATA message with the DriverCallback function.

Recording begins when the driver receives a MIDM_START message. Once the data block has been filled with data, the driver should set the MHDR_DONE bit and clear the MHDR_INQUEUE bit before notifying the client by using DriverCallback to send a MIM_DATA message.

If the driver receives data with no buffers in its input queue, it should ignore the data without notifying the client.