DriverCallback

BOOL DriverCallback(dwCallBack, uFlags, hDevice, uMsg, dwUser, dwParam1, dwParam2)

This function notifies a client application by sending a message to a window or callback function or by unblocking a task.

Returns TRUE if the callback was performed, else FALSE if an invalid parameter was passed, or the task's message queue was full.

DWORD dwCallBack

Specifies either the address of a callback function, a window handle, or a task handle, depending on the flags specified in the wFlags parameter.

UINT uFlags

Specifies how the client application is notified, according to one of the following flags.

DCB_NOSWITCH	Use this if you know you have enough stack space for the callback; otherwise MMSYSTEM will switch your stack for you.
DCB_FUNCTION	The application is notified by sending a message to a callback function. The dwCallback parameter specifies a procedure-instance address.
DCB_WINDOW	The application is notified by sending a message to a window. The low-order word of the dwCallback parameter specifies a window handle.
DCB_TASK	The application is notified by sending a message to the application or task. The low-order word of the dwCallback parameter specifies a task handle.

HANDLE hDevice

Specifies a handle to the device associated with the notification. This is the handle assigned by MMSYSTEM when the device was opened.

UINT uMsg

Specifies a message to send to the application.

DWORD dwUser

Specifies the DWORD of user instance data supplied by the application when the device was opened.

DWORD dwParam1

Specifies a message-dependent parameter.

DWORD dwParam2

Specifies a message-dependent parameter.

This function can be called at interrupt time.

The client specifies how it wants to be notified when it opens the device. The flags DCB_FUNCTION and DCB_WINDOW are equivalent to the high-order word of the corresponding flags CALLBACK_FUNCTION and CALLBACK_WINDOW specified in the dwParam2 parameter of the _OPEN message when the device was opened.

If notification is done with a callback function, hDevice, uMsg, dwUser, dwParam1, and dwParam2 are passed to the callback. If notification is done with a window, only uMsg, hDevice, and dwParam1 are passed to the window.