26 November 2013
Ethernet finds use in the automotive industry
The automotive industry is turning to Ethernet to address high-bandwidth applications emerging within the car. But it is Ethernet with a twist, tailored to meet the stringent requirements of the car. And while automotive Ethernet is taking to the road, the technology has yet to achieve widespread industry backing.
Several networking technologies have been adopted to link the electronic control units (ecus) within vehicles, which number from a dozen in simpler vehicles to as many as 150 in high end cars.
The most common in vehicle network is the CAN bus, with rates up to 2Mbit/s. The Local Interconnect Network (LIN) is a lower speed serial bus used for applications such as seat, mirror and sun roof control. FlexRay, at 10Mbit/s, is the next step up, while the Media Oriented Systems Transport (MOST) is a 150Mbit/s ring bus used for applications such as multimedia.
"Ethernet could replace MOST and has the potential to replace FlexRay, but not CAN; at least not in the near future," said Robert Schweiger, director technology solutions, automotive, EMEA at Cadence. "CAN owns the most network nodes in the car among all the network protocols."
A CAN bus interface is also used for diagnostics and to update ecu software held in flash memory. "The CAN bus is a bottleneck for flashing, updating the ecus," said Peter Hank, NXP's system architect for in-vehicle networking. "There are architectural ideas – and some implementations – where certain big ecus are interconnected with standard Ethernet to speed the [flash] updating." BMW is one car maker that has been using Ethernet for this purpose since 2008.
But it is emerging applications – car sensor systems using radar and multiple cameras to aid driving and parking, as well as in-car entertainment systems – that are sparking interest in automotive Ethernet.
Current radar systems receive sensor data and process it locally, sending the result to a central unit. "In future, we will see raw sensor data being sent to a central unit, where many different inputs will be processed and a conclusion drawn as to what is happening around the vehicle," said Toni Versluijs, general manager of in vehicle networking at NXP.
Traffic flows to and from the car will also ramp once LTE is added, linking the car to the cloud using broadband cellular. This will provide data to assist the driver while providing car makers with valuable data about the driver's habits. Ethernet will be needed to link the car's ecus to the LTE module, Versluijs added.
"Inside the car, you have multiple network islands," said Ali Abaye, senior director of automotive at Broadcom. "But car vendors want a car network; they don't want islands anymore."
Broadcom has developed a PHY to support 100Mbit/s Ethernet, dubbed BroadR-Reach, using a single unshielded twisted pair. "We can't use Cat 5 cable – four unshielded twisted pairs – it is not automotive friendly, has too many wires and is expensive and heavy," said Abaye.
Operating at 100Mbit/s over a wire pair in a harsh, electrically noisy environment requires advanced digital signal processing. BroadR-Reach has already been adopted in the BMW X5, while Hyundai has also adopted the technology.
Broadcom helped set up of the OPEN Alliance special interest group to promote BroadR-Reach as a de facto automotive Ethernet standard and the Alliance now numbers more than 200 members.
NXP has licensed the BroadR-Reach patent and is developing its TJA1100 100Mbit/s PHY. It has already demonstrated a sample PHY interoperating with Broadcom's BCM89810, but not all 100Mbit/s Ethernet PHYs are compatible. Micrel and Marvell, for example, have their own 100Mbit/s phys that are interoperable, but neither is a member of the OPEN Alliance.
The IEEE has started the Reduced Twisted Pair Gigabit Ethernet (RTPGE) working group to develop a 1Gbit/s automotive Ethernet PHY. The resulting design will be an IEEE standard, avoiding the interoperability issue at 100Mbit/s.
Unlike MOST, where the 150Mbit/s bandwidth is shared over a networking ring, automotive Ethernet allows 100Mbit/s ports to be added and scaled using Ethernet switching. But the Ethernet traffic needs additional mechanisms to ensure the car's control systems' networking requirements are met. To this aim, automotive Ethernet uses the Audio/Video Bridging (AVB) standard for Ethernet. The AVnu Alliance, with also covers professional audio and video and consumer electronics, has defined the AVB standard to enabled synchronised high bandwidth data transmission.
Cars now have as many as five cameras to assist the driver. The image and video streams from the cameras need to be synchronised to align the time sensitive views. Here, the IEEE 802.1as time synchronisation standard is used (see box). Other mechanisms include quality of service, latency control and bandwidth reservation for the traffic flows.
Broadcom offers the BCM89500 Ethernet switch that support automotive Ethernet. The seven port device has four integrated 100Mbit/s PHYs.
NXP is partnering with TTTech, known for its timed triggered Ethernet expertise, where data is sent deterministically in predefined time slots.
However, NXP is working with TTTech for its general Ethernet switch expertise. The two companies are working on a five port switch with two standard 1Gbit/s Ethernet ports and three 100Mbit/s automotive Ethernet ones, samples of which are expected by the end of 2014.
Cadence offers an Ethernet media access controller (MAC) as IP for automotive mcu, SoC and Ethernet switch designs. The MAC implements the various IEEE standards that make up automotive Ethernet. Cadence's MAC is used in Xilinx' Zynq SoC fpga. "There is an Ethernet interface on that fpga and it is our MAC," said Schweiger. Xilinx is promoting the fpga for applications that include automotive.
But challenges remain, despite the emergence of automotive Ethernet ics from several suppliers. "The biggest challenge for companies is to make a decision to introduce Ethernet, even for a subsystem," said Schweiger. "Companies are in 'observation mode' to see where the market is headed and whether there are sufficient suppliers."
NXP agrees, but points to the momentum developing around automotive Ethernet. NXP is seeing far greater interest in the technology than for FlexRay and CAN, which it also provides. "And then I see all these bandwidth requirements and new applications and driver systems, and this gives us confidence that this is the logical way to go," said Hank.
Developing a next generation 1Gbit/s PHY that will work over a twisted pair is another significant challenge. "We believe it can be done. We have done a feasibility study, we have simulations and, based on measured data from cables, we believe it is solvable," said Abaye.
Given the long development cycles of the automotive industry, a 1Gbit PHY will not be needed for several years. "A lot of applications are going to be 100Mbit/s, but there are applications – such as sending uncompressed video – that will need 1Gbit/s," said Abaye. "We don't see too many of those nodes, but the numbers will grow."
Automotive Ethernet mechanisms
Several IEEE standards make up Ethernet Audio/ Video Bridging used for automotive Ethernet. The IEEE 802.1as time synchronisation adds precise timing mechanisms to traffic, useful for image streams and in car entertainment.
The 802.1Qat stream reservation provides a way to reserve bandwidth, while the 802.1Qav queuing and forwarding performs traffic shaping and latency control. There is also the IEEE 1722 transport protocol that defines how an AVB packet is encapsulated within the Ethernet data field.