Overview

Summary

The XMOS Audio Video Bridging (AVB) endpoint is a reference design that provides time-synchronized, low latency streaming services through IEEE 802 networks. The solution is firmware that is implemented on the XMOS xCORE architecture and can be deployed on a number of different xCORE parts depending on system requirements such as stream and channel count.

images/avb_xmos_overview.png

XMOS AVB Key Features

  • 100 Mbit/s full duplex Ethernet interface via MII
  • Support for 1722.1 discovery, enumeration, command and control: ADP, AECP (AEM) and ACMP Draft 21
  • Simultaneous 1722 Talker and Listener support for sourcing and sinking audio
  • 1722 MAAP support for Talker stream MAC address allocation
  • 802.1Q Stream Reservation Protocols for QoS including MSRP, MMRP and MVRP
  • 802.1AS Precision Time Protocol server for synchronization
  • I2S, TDM and other audio interfaces for connection to external codecs and DSPs
  • Media clock recovery and interface to a PLL clock source for high quality audio reproduction

XMOS AVB Specification

Supported Standards

Ethernet

IEEE 802.3 (via MII)

AVB QoS

IEEE 802.1Qav, 802.1Qat

Precision Timing Protocol

IEEE 802.1AS

Audio Stream Encapsulation

IEEE 1722

Audio Format

IEC 61883-6 AM824

Enumeration and control

IEEE P1722.1 (Draft 21)

Supported Devices

XMOS Devices
L16-128
L12-128

Requirements

Development Tools

xTIMEComposer suite v12.0 or later

Ethernet
1 x MII compatible 100Mbit PHY

Audio
Audio input/output device (e.g. Audio CODEC)
PLL/Frequency synthesizer to generate CODEC master clock

Boot/Storage

Compatible SPI Flash Device

Licensing and Support

Reference code provided without charge under license from XMOS. Support via http://www.xmos.com/secure/tickets. Reference code is maintained by XMOS Limited.

Ethernet AVB Standards

Ethernet AVB consists of a collection of different standards that together allow audio and video to be streamed over Ethernet. The standards provide synchronized, uninterrupted streaming with multiple talkers and listeners on a switched network infrastructure.

802.1AS

802.1AS defines a Precision Timing Protocol based on the IEEE 1558v2 protocol. It allows every device connected to the network to share a common global clock. The protocol allows devices to have a synchronized view of this clock to within microseconds of each other, aiding media stream clock recovery to phase align audio clocks.

The IEEE 802.1AS-2011 standard document is available to download free of charge via the IEEE Get Program.

802.1Qav

802.1Qav defines a standard for buffering and forwarding of traffic through the network using particular flow control algorithms. It gives predictable latency control on media streams flowing through the network.

The XMOS AVB solution implements the requirements for endpoints defined by 802.1Qav. This is done by traffic flow control in the transmit arbiter of the Ethernet MAC component.

The 802.1Qav specification is available as a section in the IEEE 802.1Q-2011 standard document and is available to download free of charge via the IEEE Get Program.

802.1Qat

802.1Qat defines a stream reservation protocol that provides end-to-end reservation of bandwidth across an AVB network.

The 802.1Qat specification is available as a section in the IEEE 802.1Q-2011 standard document.

IEC 61883-6

IEC 61883-6 defines an audio data format that is contained in IEEE 1722 streams. The XMOS AVB solution uses IEC 61883-6 to convey audio sample streams.

The IEC 61883-6:2005 standard document is available for purchase from the IEC website.

IEEE 1722

IEEE 1722 defines an encapsulation protocol to transport audio streams over Ethernet. It is complementary to the AVB standards and in particular allows timestamping of a stream based on the 802.1AS global clock.

The XMOS AVB solution handles both transmission and receipt of audio streams using IEEE 1722. In addition it can use the 802.1AS timestamps to accurately recover the audio master clock from an input stream.

The IEEE 1722-2011 standard document is available for purchase from the IEEE website.

IEEE P1722.1

IEEE P1722.1 is a system control protocol, used for device discovery, connection management and enumeration and control of parameters exposed by the AVB endpoints.

The IEEE 1722.1 standard is currently in final draft and available to members of the 1722.1 Working Group

See Also