Seven messages are defined from the DDCMD entry point. Each message represents a specific request by the stream handler for the audio PDD to do perform an action.
Read and write messages allow the stream handler to get and receive data directly from the PDD without any intervention required by the application. The application neither has to send data through an IOCtl nor allocate and lock memory to perform data transfers.
Note: Refer to the Device Driver Command (DDCMD) messages in the OS/2 Multimedia Programming Reference for further information.