Design IP drives in-car entertainment and communication systems

20 April 2015

Ethernet is fast becoming the communications backbone in next-generation cars, supporting high data bandwidth applications like infotainment, ADAS and cameras. 

To help ease the development of automotive Ethernet-based systems, an ecosystem of design and verification intellectual property (IP) specifically targeting the automotive market has emerged. 

Technologies such as infotainment, ADAS, cameras, sensors, mobile connectivity, and other high-performance electronics are fuelling the next generation of automobiles. The automotive industry is adopting Ethernet as the backbone communications protocol to enable and deliver high-performance data transmission within the vehicle. To that end, the low-cost single twisted pair UTP cable enabled by automotive Ethernet technology significantly reduces cable cost and weight, making the technology a viable, ubiquitous solution for all in-car communications.

Design IP

By using design and verification IP, automotive designers can quickly bring their SoCs to the market. Cadence, for example, offers Tensilica audio/video digital signal processors (DSPs) and Ethernet-based interface IP that can be leveraged to construct end-to-end automotive electronics systems targeting various in-car applications. Tensilica HiFi audio DSPs are highly configurable and offer over 140 audio/voice CODECs, while the Tensilica imaging DSP efficiently handles camera image processing with video stabilisation, object recognition and low-light image enhancement. 

Cadence’s automotive Ethernet media access controller (MAC) specifically supports necessary requirements for the automotive market. It is capable of three different operating speeds (10/100/1000M) to enable deterministic real-time data transfer of safety-critical applications such as anti-lock breaking, while high data bandwidth, accurate timing, and quality of service can deliver audio/video stream using IEEE 802.1 AS/Qav/Qat audio/video bridging protocols. 

An audio automotive Ethernet system

Cadence has developed a technology reference system using IP cores to replicate an end-to-end automotive in-car audio system. This audio automotive system effectively illustrates a content processing and distribution communications platform for in-car audio playback consisting of an infotainment head unit and audio endpoints connected via automotive Ethernet. The audio endpoints are audio amplifiers/speakers mounted in different locations in the car with the head unit located by the driver. 

Such a system presents a synchronisation problem due to the sensitive latency and jitter requirements of the audio data. Audio data being streamed to these different endpoints must be synchronised to each other to achieve high-fidelity audio on each endpoint in the system. Ethernet is a well-established protocol which addresses these inherent synchronisation and latency problems within in-car infotainment. IEEE standards developed by the Time Sensitive Networking task group provide a common set of specifications that allow time-synchronised low-latency streaming services through Ethernet.  

Audio data streams are sensitive to jitter and latency when being transferred between the infotainment head to multiple audio endpoints. However, by transferring these audio streams using IEEE 1722 Audio Video Transport Protocol (AVTP) and utilising two distinctive features of automotive Ethernet, it is then possible to guarantee quality audio playback. Using hardware transmit and receive queues in the Cadence Ethernet MAC in addition to IEEE 802.1Qat stream reservation and IEEE 802.1Qav audio/video bridging protocol, audio streams can be distributed with the necessary bandwidth and latency requirements. Latency distortion between multiple audio endpoint channels can also be a concern as a result of different transport delays, but these can be corrected via the IEEE 1588 Precision Time Protocol.

To demonstrate the inter-workings and inter-operability of Cadence IP and its suitability as a complete automotive audio solution for SoCs, Cadence has developed an emulated audio endpoint running on an FPGA platform. Audio streams are transported over automotive Ethernet representing music playback to in-car audio speakers. Figure 2 shows how the audio system has been designed and developed using various IP blocks.

IEEE 1722 AVTP Ethernet packets are streamed from a talker PC emulating the infotainment head unit over Ethernet using BroadR-Reach PHY and a single twisted pair cable. These packets are received by the Ethernet MAC and written to DDR memory for processing. The Tensilica processor running Linux and an AVB software stack is used to manage and process these audio streams and then transfer them to the HiFi processor for further post processing or to the I2S interface for playback. 

Both the infotainment head unit and audio endpoint run a Linux OS with an AVB software stack built on top. Both software implementations use gPTP, which allows them to keep their time synchronised with an accuracy measured in nanoseconds.

The application which streams audio is known as the Talker. This reads an audio file in PCM format, then uses the Open-AVB stack to transmit samples in IEEE 1722 format packets at fixed intervals. A presentation timestamp is embedded in each packet to indicate the time at which each sample should be played back.

The application which receives audio is known as the Listener. This uses MRP (Multiple Registration Protocol) to register its attributes as a listener. Next, it uses the PCAP API to read each IEEE1722 format packet as it is received and then buffers the data until it is time to play.

The left audio channel on the talker is played, while the right audio channel is played on the Listener. Where the two clocks are synchronised, this results in the audio being exactly aligned. Figure 3 illustrates the synchronisation and latency issues that arise in such a system.

Design methodology

Rather than use a traditional verification methodology to validate the design, the audio automotive Ethernet system was verified in the system environment to enable firmware development as soon as possible in the design cycle. Cadence’s Palladium XP platform offers a hardware emulation platform where users can verify their designs within a systems environment. In-circuit emulation (ICE) via a Cadence SpeedBridge Adapter for Ethernet and a JTAG debugger connects the Palladium XP platform to a prototype of the audio automotive Ethernet system, providing a transparent connection to real-world systems. Using the Palladium XP platform in ICE mode with an Ethernet SpeedBridge adaptor allowed fast verification of the interconnections and interoperability of each IP block within the design using bare-metal software tests.
Development board

RIPE2 is a Cadence FPGA development board that allows rapid IP evaluation. It has various connectors available to populate with different types of daughter boards. For example, the audio automotive Ethernet system uses two daughter boards:

• Broadcom BroadR-Reach PHY daughter board for automotive Ethernet data communications
• I2S audio daughter board for music playback

Using RIPE2, BroadR-Reach PHY and audio daughter boards provided the platform to prove both the RTL design and software, creating a true audio automotive Ethernet endpoint system demonstrating an end-to-end in-car infotainment application.

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