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USB Audio Design Guide
Since the Vendor_ReadHidButtons() function is called from the buffer logical core,
care should be taken not to add to much execution time to this function since this
could cause issues with servicing other endpoints.
For a full example please see the HID section in §6.1.
4.4 Apple MFi compatibility
XMOS devices are capable of operating with Apple iPod, iPhone, and iPad devices
that feature USB host support. Information regarding this functionality is protected
by the Made For iPod (MFi) program and associated licensing.
Please contact XMOS for details and further documentation.
4.5 Audio Stream Formats
The design currently supports up to 3 different stream formats for output/playback,
selectable at run time. This is implemented using Alternative Settings to the
AudioStreaming interfaces.
An AudioStreaming interface can have Alternate Settings that can be used to change
certain characteristics of the interface and underlying endpoint. A typical use of
Alternate Settings is to provide a way to change the subframe size and/or number
of channels on an active AudioStreaming interface. Whenever an AudioStreaming
interface requires an isochronous data endpoint, it must at least provide the
default Alternate Setting (Alternate Setting 0) with zero bandwidth requirements
(no isochronous data endpoint defined) and an additional Alternate Setting that
contains the actual isochronous data endpoint.
For further information refer to 3.16.2 of USB Audio Device Class Definition for
Audio Devices
Note, a 0-bandwidth alternative setting 0 is always implmented by the design (as
required by the USB specifications).
Customisatble parameters for the Alternate Settings are as follows.:
Audio sample resolution
Audio sample subslot size
Audio data format
Currently only a single format is supported for the input/recording stream
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