OS X and iOS Kernel Programming

Multi-Function Drivers

USB and PCI devices may be composite devices that include multiple independent devices in which each device's separate driver can handle each function. Other devices may consist of one logical device handled by multiple drivers. Let's consider a modern graphics card with an HDMI output port as an example. HDMI is able to carry both audio and video, so it would be nice to provide an audio driver that allowed the device to be used with Core Audio. The device is a graphics card, so the hardware doesn't have the typical DMA engine of most audio hardware. Instead, audio data is sent along with video frames at regular vertical blanking intervals. This design means that the audio and video parts are intimately linked and need ...