simplifying implementation of automotive ethernet for

Simplifying Implementation of Automotive Ethernet for Infotainment Applications

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Simplifying Implementation of Automotive Ethernet for Infotainment Applications From high-performance navigation systems to high-end entertainment and telematics, the system requirements of the ‘always on / connected car’ are fuelling demands to increase the bandwidth available for in-vehicle data communications. As a result, engineers are turning to Ethernet – a proven technology that not only supports the high data rates demanded by next-generation infotainment systems but can also simplify cabling and network interfaces and drive down costs. And the latest semiconductor technologies are helping to simplify and speed in-vehicle Ethernet implementation. The role of the car is changing. Until now, it has been a means of getting from A to B in style, safety or speed – depending on the car you select. Increasingly, intelligent infotainment systems are making the car an extension of their owner’s digital lifestyle – keeping them connected to social media and email while on the move as well as facilitating easier, smoother and more efficient journeys by being connected to traffic reports and weather information. In fact, the infotainment system is becoming a key differentiator for car manufacturers in the eyes of the consumer. At the same time, government-mandated safety systems such as reversing cameras are contributing to the need for effective, reliable and fast data communications. And, as the car becomes increasingly data hungry, the demand for effective, reliable and high-speed communications is growing.

Introduction There are several choices of media communications protocol available – CAN, LIN, FlexRAY and MOST have all contributed to the growth of automotive networking. Each has certain limitations ranging from low speeds or lack of strong security to poor scalability and, in some cases, a limited (or sole) supplier base. Ethernet is emerging as the leading contender to be the future of automotive networking. One of the most established protocols in automotive applications is the Controller Area Network (CAN) bus. Originally developed by Robert Bosch GmbH around 30 years ago, CAN is a bi-directional, packetized, multi- master serial bus for connecting nodes of varying complexity. CAN was originally developed for communicating status updates from sensors and peripherals to the main Engine Control Unit (ECU). The primary limitation with CAN had been its bandwidth. In early implementations CAN frames were typically quite small (50 to 100 bits in length) and the bus speed was 1Mbit/s at most. This is perfectly adequate for slower status updates from sensors but does not possess the capacity for the high- bandwidth data requirements of today’s infotainment systems. In 2011, Bosch started development on CAN- FD (CAN-Flexible Data Rate), which allows the transmission of data at speeds higher than 1Mbit/s by increasing speeds during the data transmission phase. The Media Oriented Systems Transport (MOST) bus is a high-speed multimedia network technology based on plastic optical fibre (POF) and is used by European and Japanese car manufacturers. It is limited to 64 devices on a ring configuration. The latest incarnation of MOST (MOST150) allows up to 150Mbit/s (six times that of the original MOST25) over a coaxial cable and is capable of providing a physical layer to implement Ethernet in cars – allowing the transmission of all forms of data, including video. Ethernet is rapidly becoming a popular choice for infotainment systems – it is the most prevalent communications protocol available today. The technology is well understood and the components are freely available at relatively low

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cost. Currently, Ethernet offers up to 100Mbit/s in automotive applications but a 1Gbit/s standard based on reduced twisted pair (RTPGE) is about to be finalised by the IEEE and speeds of up to 10Gbit/s are being discussed. One of the limitations of Ethernet is the CSMA/CD protocol that manages the contention (collisions) between devices on the same bus by introducing exponentially increasing delays until one device grabs the bus and transmits successfully. This works well for non-critical applications but as Ethernet takes on a wider role within vehicles, a more managed approach is needed.

Market estimates for automotive Ethernet During 2013, there were approximately 3.8M nodes shipped. Japanese analyst Yano Research predicts this to reach 50M nodes this year and exceed 200M nodes by 2020. Their forecast predicts that camera systems will account for around 75%, infotainment will be 25% and On-Board Diagnostics (OBD) and the fundamental backbone will be present, but small. A forecast by Strategy Analytics broadly agrees the overall numbers (175M nodes by 2020) but sees a much more equal split between OBD, cameras and infotainment.

The Gigabit Ethernet AVB standard Audio Visual Bridging (AVB) enables stable, reliable, multimedia transmissions and refers to a set of technical standards being developed by the IEEE. The working group was renamed to the Time-Sensitive Networking Task Group in 2012 to reflect the expanded scope of their role. The relevant IEEE standards are all under the 802.1 standards committee and comprise:-

• IEEE 802.1BA: Audio Video Bridging (AVB) Systems; • IEEE 802.1AS: Timing and Synchronization for Time-Sensitive Applications (PTP); • IEEE 802.1Qat: Stream Reservation Protocol (SRP); and • IEEE 802.1Qav: Forwarding and Queuing for Time-Sensitive Streams (FQTSS).

An AVB network can contain AVB-capable and non-AVB-capable devices. As we shall see, the ability to implement the AVB protocols fully is key and while legacy traffic can flow freely around the system, only certain domains in a mixed system can be considered ‘AVB-capable’ based upon the arrangement and interconnection of the nodes. The IEEE 802.1BA (AVB) standard describes the way in which non-AVB (‘unmanaged’) bridges are identified and flagged. Once the basic link criteria of IEEE 802.3 is met then the following criteria determine if a bridge can be considered AVB-capable.

• The link is full duplex at 100Mbit/s or greater • The 802.1AS protocol discovers exactly one peer • The 802.1AS protocol measures a round-trip delay of no more than a worst case wire delay • An SRP reservation request or acknowledge is received on the port

The basic principle behind AVB is that it reserves a portion of the available Ethernet bandwidth for AVB-related packets. These packets are sent regularly in allocated slots in the reserved bandwidth, thus avoiding any collisions. Each packet has a presentation time that defines when the data in the packet should be played out.

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Another fundamental principle of AVB is the Stream Reservation Protocol covered by IEEE 802.1Qat. The AVB- related traffic on the network is divided into real-time traffic and ‘everything else’. The real-time traffic has a slot every 125uS (8kHz) – all of the other AVB-related traffic is then transmitted outside this slot within the bandwidth allocated to AVB. The non-AVB traffic is then fits into in the non-AVB bandwidth.

Figure 1 – The diagram shows two possible AVB bandwidth allocation scenarios. As the AVB bandwidth expands (lower example) then the possibility for legacy data to be delayed increases. The protocol also allows for nodes to allocate bandwidth between themselves based upon the likely levels of data to be transmitted. Figure 3 below shows a simple system with four nodes and two switches. As an example, if 70Mbit/s is allocated for AVB, then 45Mbit/s could be allocated for the data to travel over the central link, while the communication between B and C occupies the remaining 25Mbit/s.

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Figure 2 – A simple AVB system where the bandwidth between nodes is apportioned to ensure availability of the main backbone. Critical to realising an AVB architecture is that all nodes implement SRP and send real-time traffic based upon the 8kHz heartbeat. With timing being so critical, an AVB system relies on the Precision Time Protocol (PTP) (802.1AS) to manage the system clocks, based upon an initial assumption that each of the nodes has a crystal clock with an accuracy around 25ppm. The node with the most accurate clock is defined as the ‘master’ and then, through regular messages, each of the other nodes compute their skew and adjust locally to maintain an accurate local clock. One of the challenges associated with this comes about if there is an unstable clock in the system (for example a high level of thermal drift). If the clock-sync process is carried out infrequently, then there can be phase differences in the system – if it is carried out too often then bandwidth is taken up and jitter can be introduced into the system.

Why dedicated Ethernet SoCs are required for automotive One of the reasons that Ethernet AVB will dominate the market for automotive data communications is that the basic Ethernet architecture is extremely well understood and used in so many high-volume applications. This means that there is a large pool of capable design engineers as well as a large supplier base that gives security of supply and competitive pricing. However, the basic components are designed and qualified primarily for office or industrial applications – they are not suitable for automotive applications. In order to move into the automotive world the components need to be qualified to the relevant Automotive Electronics Council (AEC) standard – AEC-Q100. The AEC standard is very comprehensive and defines a substantial number of electrical, lifetime and reliability tests that are more stringent than those for a commercial or industrial IC. AEC-Q100 defines five temperature ranges depending on where in the vehicle the IC will be deployed. Grade 0 is the most stringent (-40°C to +150°C) and is for drivetrain components. At the lower level, the temperature ranges for Grades 3 and 4 correspond closely to industrial and commercial levels.

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Silicon support for high-resolution multimedia and camera connectivity One of the latest devices to enter the world of AVB is an automotive-grade Ethernet bridge solution for in- vehicle infotainment (IVI), telematics and other automotive applications from Toshiba Electronics Europe (TEE). The TC9560XBG supports IEEE 802.1AS and IEEE 802.1Qav. The device has been developed under the ISO/TS 16949 and APQP automotive design quality system and is in the process of being AEC-Q100 Grade 3 qualified. When connected to an application processor or other system-on-chip (SoC) host, the TC9560XBG allows the host device to deliver audio, video, and other data through the automotive AVB network. A freely programmable, on-chip, ARM® Cortex-M3 processor running at 187.5MHz performs system control and management and with the DMA controllers gives wide access to all system resources including the version 2.0 and 1.0 compliant PCIe bus (5GT/s or 2.5GT/s) for future extension and development. The Ethernet bridge solution has a comprehensive specification including 512kB of SRAM, 6 channels of DMA, a full duplex UART and multiple control interfaces including USB HSIC (480Mbit/s), I2C, quad SPI, TDM/I2S and up to 36 GPIO pins. Power management is achieved via a low power mode with Wake-on-LAN (WoL) support. Security features include built-in SHA2 and eFUSE support.

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The A-version TC9650AXBG also offers two channels of CAN-FD in addition.

Figure 3 – Block diagram of the sophisticated TC9560XBG AVB Ethernet Bridge The primary application of the TC9560XBG is to provide the interface between the Ethernet (AVB) nodes and the SoC used in the system. As such, the bridge is found in many different applications throughout the vehicle including telematics, audio subsystems, instrumentation and also within the head unit. In each case, the TC9560XBG is responsible for ensuring the correct implementation and operation of the IEEE AVB protocols within the system.

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Figure 4 – The key function of the TC9560XBG is to provide the interface to the Automotive Ethernet network The AVB bridge is a key part of TEE’s automotive product line-up, which also includes the TC358791XBG automotive companion chip that drives high-resolution multimedia (audio, video) and camera connectivity for next-generation infotainment applications in the connected car. Supporting the latest automotive Gigabit Ethernet AVB standard for a wide range of applications, such as front/rear/surround-view cameras, digital audio and transferring high-resolution video content to head-unit and rear-seat entertainment systems, the TC358791XBG can also seamlessly interface with and support many leading-edge automotive application processors, due to its USB 3.0 and MIPI® CSI2 and DSI connectivity for both audio and video. The TC358791XBG can split one video input into two pictures and can simultaneously drive two high-resolution low-voltage differential signalling (LVDS) digital displays. Examples include head units, instrument clusters, and parking aid vision systems. The chip can also send high-resolution audio and video data from the host processor to multiple displays or other electronic control units in the car, and it has a High Definition Multimedia Interface (HDMI®) 1.4 receiver interface to connect smartphones and other HDMI-enabled devices to the application processor. TEE is further supporting the rapid development of AVB systems by providing two development systems including an evaluation board with full connectivity and a PCIe form factor board that can be plugged directly into a PC or used in a stand-alone mode.

Summary Automotive Ethernet has reached a pivotal point in its development. As more chipsets are qualified to automotive grade and manufacturers support the design function with sophisticated tools, development boards and reference designs, then the pace of implementation and adoption will accelerate. Initially, the focus will be on infotainment and high-bandwidth devices such as cameras, but the development of automotive Ethernet to 1GB speeds and, ultimately, 10GB

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will, of itself, bring further opportunities as the industry continues the drive towards the fully connected self-driving vehicles of the future.

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