The Usb Audio System Architecture; Xmos Usb Device (Xud) Library - XMOS xCORE-200 Multi-channel Audio board Design Manual

USB Audio Design Guide

3.1 The USB Audio System Architecture

The XMOS USB Audio platform consists of a series of communicating components.
Every system is required to have the shared components listed in Figure 7.
Component
XMOS USB Device Driver (XUD)
Endpoint 0
Endpoint buffer
Decoupler
Figure 7:
Shared
Audio Driver
Components
In addition Figure
Component
Mixer
S/PDIF Transmitter
S/PDIF Receiver
ADAT Receiver
Clockgen
Figure 8:
MIDI
Optional
PDM Microphones
Components
Figure
represent cores with arrows indicating inter-core communications.
This section will now examine these components in further detail.

3.2 XMOS USB Device (XUD) Library

All low level communication with the USB host is handled by the XMOS USB Device
(XUD) library.
The XUD_Manager() function runs in its own core and communicates with endpoint
cores though a mixture of shared memory and channel communications.
XM0088546.1
8 shows components that can be added to a design:
Description
Allows digital mixing of input and output channels. It can also
handle volume control instead of the decoupler.
Outputs samples of an S/PDIF digital audio interface.
Inputs samples of an S/PDIF digital audio interface (requires the
clockgen component).
Inputs samples of an ADAT digital audio interface (requires the
clockgen component).
Drives an external frequency generator (PLL) and manages
changes between internal clocks and external clocks arising from
digital input.
Outputs and inputs MIDI over a serial UART interface.
Receives PDM data from microphones and performs PDM to PCM
conversion
9 shows how the components interact with each other. The green circles
Description
Handles the low level USB I/O.
Provides the logic for Endpoint 0 which handles
enumeration and control of the device including DFU
related requests.
Buffers endpoint data packets to and from the host.
Manages delivery of audio packets between the
endpoint buffer component and the audio components.
It can also handle volume control processing.
Handles audio I/O over I2S and manages audio data
to/from other digital audio I/O components.
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