USB AUDIO 2.0 REFERENCE DESIGN XMOS, USB AUDIO 2.0 REFERENCE DESIGN Datasheet - Page 18

• Manufacturer Part Number: USB AUDIO 2.0 REFERENCE DESIGN
• Description: USB AUDIO 2.0 REFERENCE DESIGN
• Manufacturer: XMOS

Specifications of USB AUDIO 2.0 REFERENCE DESIGN

• Design Resources: USB AUDIO Schematic
• Main Purpose: Audio, Audio Processing
• Embedded: Yes
• Utilized Ic / Part: XS1-L1
• Primary Attributes: Audio data up to 24-bit @ 192kHz
• Secondary Attributes: I²S and S/PDIF
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 880-1017

When changing the volume, Endpoint 0 applies the master volume and channel
The volume will either be handled by the decoupler or the mixer component (if the
This thread is implemented in the file
This thread is also responsible for feedback calculation based on SOF notification
USB Audio Software Design Guide
Audio Request: Setting The Sample Rate
sample rate, it sends a command to Endpoint 0. The device initiates a reset. When
the device restarts, the new sample rate is registered with the audio driver thread.
Audio Request: Volume Control
sends an audio interface request to Endpoint 0. An array is maintained in the
Endpoint 0 thread that is updated with such a request.
volume, producing a single volume value for each channel. These are stored in the
array.
mixer component is used). Handling the volume in the mixer gives the decoupler
more performance to handle more channels.
If the effect of the volume control array on the audio input and output is implemented
by the decoupler, the decoupler thread reads the volume values from this array.
Note that this array is shared between Endpoint 0 and the decoupler thread. This is
done in a safe manner, since only Endpoint 0 can write to the array, word update is
atomic between threads and the decoupler thread only reads from the array (ordering
between writes and reads is unimportant in this case). Inline assembly is used by the
decoupler thread to access the array, avoiding the parallel usage checks in XC.
If volume control is implemented in the mixer, Endpoint 0 sends a mixer command
to the mixer to change the volume. Mixer commands are described in Section 3.7.
3.4.3 Audio Endpoints (Endpoint Buffer and Decoupler)
Endpoint Buffer
to the XUD library and as such it simply receives or transmits buffers which are
passed to it via shared memory from the decoupler.
and reads from the port counter of a port connected to the master clock.
1. Depending on the DFU state, the device may be set into DFU mode.
2. A message is sent to the audio driver to alert it of an impending reset. At this
3. The low-level XUD function is called to perform a USB reset.
point audio capture/playback is stopped until the device restarts.
All endpoints other that Endpoint 0 are handled in one thread.
When the host requests a volume change, it
usb_buffer.xc . This loop must be responsive
When the host requests a change of
Document Revision 1.2
18/57