Applications access user-mode driver capabilities by passing messages to standard driver entry points.
All Win32-based user-mode drivers must export an entry point function called DriverProc. This function receives a set of messages known as the standard driver messages. Generally, a user-mode driver’s DriverProc function also recognizes additional customized driver messages.
A default message handler, called DefDriverProc, is provided within winmm.dll. Every user-mode driver should call DefDriverProc from within its DriverProc function, if it receives an unrecognized or unsupported message.
User-mode audio device drivers provide additional entry point functions.
All driver entry points must be exported in a module definition (.def) file.