Program Flow

The following figure illustrates how the DUET1 sample program interfaces with the Media Device Manager (MDM) to handle the concept of grouping. Source code for DUET1 is located in the \TOOLKIT\SAMPLES\MM\DUET1 subdirectory.

                              ┌───────────────┐
                              │    DUET1      │
                              │    Sample     │
                              │    Program    │
                              └───┬───────┬───┘
                               ┌──┘  (1)  └─┐
                                           
                ┌────────────────┐          ┌────────────────┐
                │   Waveform     │          │   Waveform     │
                │     Audio      │          │     Audio      │
                │Device Context 1│   (2)    │Device Context 2│
                └────────────┬───┘          └──┬─────────────┘
                             └─┐             ┌─┘
                                            
                              ┌───────────────┐
                              │ Media Device  │
                              │    Manager    │
                              │               │
                              └───────┬───────┘
                                      │
┌────┐                                
│WAVE│                        ┌───────────────┐
│File│┐                      │   Waveform    │
└────┘ │  ┌─┐                 │ Audio Media   │
       └─│M│                 │    Driver     │
          │M│                 └───────┬───────┘
       ┌─│I│                    (3)  │
       │  │O│                         
┌────┐ │  └─┘                 ┌───────────────┐
│WAVE│┘                     │  Sync/Stream  │
│File│     │                  │    Manager    │
└────┘     │                  │               │
           │                  └───────────────┘
           │                               
           │       ┌────────────┘           └────────────┐
           │                                            
     ┌─────┴────────┐                (4)           ┌──────────────┐
     │  File System │            ┌─┬─┬─┬─┬─┐       │     Audio    │
     │Stream Handler├────────────┤ │ │ │ │ ├───────┤Stream Handler│
     └──────────────┘            └─┴─┴─┴─┴─┘       └──────┬───────┘
                                                            (5)
                                                   ┌──────────────┐
                                                   │   Audio DD   │
                                                   │              │
                                                   └──────┬───────┘
                                                          
                                                   ┌──────────────┐
                                                   │   Audio HW   │
                                                   │              │
                                                   └────────┐    ┌┘
                                                            └────┘

• The DUET1 program directly interfaces with media control interface services using the procedural interface.

  Each part of the duet is played through the OS/2 multimedia system using a separate instance of a logical media device. In this case, it uses two instances of the logical waveform device, the Waveform Audio Media Driver. When the Duet Player is ready to play a song, it issues the MCI_GROUP command to the MDM to set up a group of two logical waveform devices. The MDM returns a group handle to the application, so that the application can refer to that group as a single unit (instead of having to manage each logical device separately). The MDM handles the management of the logical media devices for the application.

• The MDM sets up two Waveform Audio Media Drivers as a group.

• The Waveform Audio Media Driver handles the creation and management of the source and target stream handlers. In this example, the source stream handler is the File System Stream Handler, and the target stream handler is the Audio Stream Handler. When the Waveform Audio Media Driver receives an MCI_OPEN command from the program, it creates the stream handlers.

  When you select Play, Pause, or Stop, the application issues an MCI_PLAY, MCI_PAUSE, or MCI_STOP message to the MDM. The MDM then passes this message to the appropriate media devices in the group.

• The media driver issues SPI functions to the Sync/Stream Manager (SSM) to process the play, pause, resume, and close messages from the application. The SSM controls the registration and activities of all stream handlers. SPI services enable media drivers to create, start, and end data streams. SPI also provides real-time services to enable stream handlers to synchronize events. The File System Stream Handler and the Audio Stream Handler are responsible for controlling the flow of application data in a continuous, real-time manner.

• The target stream handlers interface with the audio device driver through the inter-device-driver communication (IDC) interface. This is the interface between the stream handler and the physical device driver (PDD). The IDC interface includes Stream Handler Device (SHD) messages and device driver command (DDCMD) messages.
  

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