Ethernet tackles automotive EMI challenge

Real-time performance
Solutions based on interoperable standard Ethernet provide a simple, inexpensive route for Ethernet semiconductor manufacturers to offer low emission solutions based on their existing 100Base-TX technology. Any non-Ethernet PHY approach echoes the criticism directed towards MOST technology and the increasing preference towards Ethernet based solutions.

Real-time performance with Ethernet is relatively straightforward with the necessary quality of service (QoS) guaranteed by use of IEEE Audio Video Bridging (AVB) specifications. The AV Bridging system is based on three specifications:

• IEEE 802.1as Time Synchronization
• IEEE 802.1Qat Stream Reservation
• IEEE 802.1Qav Queuing & Forwarding for AV Bridges

Time synchronization is critical in order to ensure quality audio and video streaming within an Ethernet network. IEEE 802.1as utilizes specific PTP (Precise Time Protocol) packets to provide synchronization across the network to a common system clock source. Nodes in the network, known as Time-Aware Bridges, will extract timing from the network based on a series of PTP synchronization message exchanges with the master clock source and neighbours.

Micrel recently introduced the new EtherSynch™ family of highly integrated Ethernet devices, supporting both IEEE 1588v2 and IEEE 802.1as time synchronization protocols. Timing accuracy in the order of sub 100ns can be comfortably achieved; outperforming the IEEE based standards (1us), enabling suitability for control application as well as A/V streaming. The family of PTP devices is offered in the form of a 3-Port switch with MII or RMII, 2-Port and Single-Port Controllers with 8/16-bit host processor interface. All devices feature embedded ultra low power PHY transceivers, time precision GPIO in a compact 10mm x 10mm 64-LQFP package. 

IEEE 802.1Qat Stream Reservation allows network bandwidth and buffer resources to be reserved for specific traffic schemes using SRP (Stream Reservation Protocol). IEEE 802.1Qav Queuing and Forwarding methods are based on segregating traffic into isochronous (time critical) and asynchronous (non-time critical) packets and prioritising using the priority class defined in IEEE 802.1p. Egress port buffers are then separated into two or more queues, each allocated to a specific priority class. Isochronous packets will be given the highest priority, while asynchronous packet the lowest.  A credit based traffic shaper is defined to smooth the ‘bursty’ nature of video data.

Conclusion

If Ethernet is going to be adapted as a true automotive network bus, then automotive makers will demand a commonly agreed solution that is open and freely accessible. Talk to industrial control manufacturers and they will certainly agree, based on their experiences with original multiple, non-interoperable field bus standards, now which are based on Ethernet. Progress is already underway for next generation vehicle networks with the formation of a new IEEE 802.3 Gigabit Ethernet Study Group for Automotive.

Ethernet’s unquestionable success in the Industrial networking sector has proven reliability and quality in an extreme environment. This marriage of this industrial strength and consumer technology drive provides the perfect physical layer solution for automotive, successfully bridging the gap between lengthy vehicle design cycles and today’s fast moving IP world.

Today, Ethernet has already emerged inside the car to provide an IP-based standard interface for diagnostics and software downloading. The next step is for Ethernet to form the backbone of the next generation automotive multi-media networks, carrying ‘live’ traffic. New standards such as IEEE 802.3AVB (Audi-Video Bridging) provide necessary real-time performance, while multiple suppliers already offer proven low EMI emission Ethernet, interoperable both with each other and any other IEEE 802.3 Ethernet PHY. 

There is nothing complex about Ethernet technology overall; it is simple, proven and open — the reason for its success. Cost is a crucial factor in any market and Ethernet has consistently demonstrated the lowest cost of ownership of any network.

About the author: Mike Jones is Senior Marketing Manager for Micrel Inc. Mr. Jones has more than 20 years high tech design experience in the semiconductor industry. He is currently based in Newbury, U.K., where he is responsible for Micrel Semiconductor Ltd’s European applications for High Speed Networking and Ethernet solutions. Prior to coming to Micrel, Mr. Jones worked for several high tech companies, in various engineering roles, including as a development engineer at BT and Fujitsu Telecommunications where he gained more than a decade in design experience in SONET, SDH and PDH systems. He was a senior FAE with Micrel for ten years prior to his current position.