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USB Audio Design Guide 14/61

The Endpoint 0 core controls the enumeration/conﬁguration tasks of the USB

device.

The buﬀering core sends/receives data packets from the XUD library. The core

receives audio data from the decoupler core, MIDI data from the MIDI core etc.

3.5.1 Endpoint 0: Management and Control

Endpoint 0 (

endpoint0.xc

) controls the management tasks of the USB device.

These tasks can be generally split into enumeration, reset, audio conﬁguration and

ﬁrmware upgrade.

3.5.2 Startup/Enumeration

When the device is ﬁrst attached to a host, enumeration occurs. The device presents

several interfaces to the host via a set of descriptors.

Mode Interfaces

Application mode Audio Class 2/Audio Class 1

DFU Class 1.1

MIDI Device Class 1.0

DFU mode DFU Class 1.1

Figure 7:

USB devices

presented to

host

The device initially starts in Application mode.

§3.7 describes how DFU mode is used. The audio device class (1 or 2) is set at

compile time—see §5.1.

Common enumeration requests are largely handled by the call to

DescriptorRequests()

using data structures found in the

descriptors_2.h

ﬁle.

These structures use deﬁnes which can be customized—see §5.1.

This function returns 0 if the request was fully handled (and thus no further action

is required). The function returns 1 if the request was not recognised by the

DescriptorRequests()

function and further parsing is required to deal with the

request. The function returns -1 if a USB bus reset has been communicated from

XUD to Endpoint 0.

3.5.3 Reset

On receiving a reset request, three steps occur:

1. Depending on the DFU state, the device may be set into DFU mode.

A XUD function is called to reset the endpoint structure and receive the new

bus speed.

REV 6.1

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