MODM_OPEN

See also MODM_CLOSE, MIDIOPENDESC

Sent to a MIDI output driver to allocate a specified device for use by a client application.

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_ALLOCATED	The device is already allocated by the maximum number of clients the driver supports or the device cannot be opened because of system resource limitations other than memory.
MMSYSERR_NOMEM	The device cannot be opened because of a failure allocating or locking memory.

DWORD dwParam1

Specifies a far pointer to a MIDIOPENDESC structure. This structure contains additional information for the driver such as instance data from the client and a callback for the client.

DWORD dwParam2

Specifies option flags for opening the device.

CALLBACK_EVENT	If this flag is specified, dwCallback in the MIDIOPENDESC structure is assumed to be an event handle.
CALLBACK_FUNCTION	If this flag is specified, dwCallback in the MIDIOPENDESC structure is assumed to be the address of a callback function.
CALLBACK_THREAD	If this flag is specified, dwCallback in the MIDIOPENDESC structure is assumed to be a handle to a thread.
CALLBACK_WINDOW	If this flag is specified, dwCallback in the MIDIOPENDESC structure is assumed to be a window handle.
MIDI_IO_COOKED	If this flag is specified, the device is being opened in stream mode. In stream mode, the driver may receive all Windows 3.1 messages as well as the stream messages. The device driver must be able to handle any contingencies which arise; for example, it must be able to play short messages and system exclusive messages asynchronously to the stream.
MIDI_IO_PACKED	If this flag is specified, the driver is being opened in compatability mode. (Compatability mode is supported for applications written for the Windows 3.1 platform).

It is up to the driver to determine the number of clients allowed to use a particular device. Once a device is opened for the maximum number of clients the driver supports, the driver should return MMSYSERR_ALLOCATED for any additional open requests. If the open operation is successful, the driver should use the DriverCallback function to send the client a MOM_OPEN message.