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USB Audio Design Guide 13/61

3.4.1 Driver Support

Audio Class 1.0 had been fully supported in Apple OSX for many years. Audio

Class 2.0 has been fully supported in Apple OSX since version 10.6.4.

Audio Class 1.0 is fully supported in all modern Microsoft Windows operating

systems (i.e. Windows XP and later). Audio Class 2.0 is not supported natively by

Windows operating systems, a driver is required to be installed. Please contact

XMOS for further details.

3.4.2 Audio Class 1.0 Mode and Fall-back

The normal default for XMOS USB Audio applications is to run as a high-speed

Audio Class 2.0 device. However, some products may prefer to run in Audio Class

1.0 mode, this is normally to allow “driver-less” operation with Windows operating

systems.

Note: To ensure speciﬁcation compliance, Audio Class 1.0 mode always operates

at full-speed.

The device will operate in full-speed Audio Class 1.0 mode if:

· The code is compiled for USB Audio Class 1.0 only.

The code is compiled for USB Audio Class 2.0 and it is connected to the host

over a full speed link (and Audio Class fall back is enabled).

The options to control this behavior are detailed in §5.1. When running in Audio

Class 1.0 mode the following restrictions apply:

· MIDI is disabled.

DFU is disabled (Since Windows operating systems would prompt for a DFU

driver to be installed)

Due to bandwidth limitations of full-speed USB the following sample-frequency

restrictions are also applied:

Sample rate is limited to a maximum of 48kHz if both input and output are

enabled.

Sample rate is limited to a maximum of 96kHz if only input or output is enabled.

3.5 USB Interface

The low-level USB interface is controlled by the XMOS USB Device (XUD) driver. This

driver is described in the XUD library documentation

The low level USB interface communicates with two other cores:

http://www.xmos.com/published/xuddg

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