MODM_GETNUMDEVS

The MODM_GETNUMDEVS message requests a MIDI output driver to return the number of device instances that it supports.

Parameters

uDeviceId

Device identifier (0, 1, 2, and so on) for the target device.

uMsg

MODM_GETNUMDEVS

dwUser

Device instance identifier.

dwParam1

Not used.

dwParam2

Not used.

Return Value

The driver returns the number of MIDI output device instances it supports.

Comments

A client sends the MODM_GETNUMDEVS message by calling the user-mode driver’s modMessage entry point, passing the specified parameters.

The driver should return the number of logical MIDI output devices that can be supported. Typically, for each physical device, a kernel-mode driver can support one or more logical devices of various types. For example, for each Creative Labs Sound Blaster card, there are MIDI, waveform, mixer, and auxiliary audio devices. Kernel-mode drivers store logical device names and types in the registry under the path HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DriverName\Parameters\DeviceNumber\Devices. To correctly return the number of logical devices, the user-mode driver should examine the \Devices subkey for each of the driver’s \DeviceNumber keys, searching for logical devices of the desired type. (Code in drvlib.lib provides this capability.)