Hardware Dev Center

DirectMusic DDI Overview

The design principles that are needed to implement user-mode synths generally apply to kernel-mode synths as well. For this reason, this guide begins with a discussion of user-mode implementations and progresses to specific kernel-mode topics.

Typically, the best design strategy is to first write a software implementation of the DirectMusic device driver interface (DDI) that runs in user mode. This approach is beneficial even if the final product is a kernel-mode implementation that uses hardware components. After the user-mode version is completed, the software can be converted to kernel mode and connections established with the hardware, one feature at a time. For more information, see User Mode Versus Kernel Mode.

DirectMusic uses the following user-mode interfaces to control user-mode synthesizers and communicate with kernel-streaming drivers:


This is the user-mode interface for implementing custom software synths.


This is the user-mode interface for implementing custom wave sinks in Microsoft DirectX 6.1 and DirectX 7. In DirectX 8 and later, DirectMusic always uses its private wave sink with a user-mode synth, and no public interface is supported for user-mode wave sinks.


DirectMusic uses this interface to access the properties of kernel-streaming drivers from user mode in DirectX 6.1 and later.

Kernel-mode terminology differs slightly from user-mode because of the port-miniport driver model (see Introduction to Port Class), which delegates generic kernel-streaming tasks to the DMus port driver and assigns hardware-specific functions to the DMus miniport driver. The port and miniport drivers share responsibilities for the synth. The kernel-mode wave sink is part of the kernel-resident port driver. Unlike the user-mode wave sink in DirectX 6.1 and DirectX 7, the kernel-mode wave sink is not replaceable. Most of the work that is required to build a custom kernel-mode driver is in the writing of the miniport driver. In most cases, the miniport driver is the only component that the driver writer needs to implement to support a piece of hardware, or to implement a custom software synth for DirectMusic.

Custom DMus miniport drivers use the following kernel-mode interfaces:







DMus miniport drivers implement the IMiniportDMus, ISynthSinkDMus, and IMXF interfaces. The DMus port driver implements the IAllocatorMXF, IMasterClock, and IPortDMus interfaces and exposes them to miniport drivers.



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