The Ethernet is Coming For Your Ride

January 16, 2019 John Burkhert

The Ethernet is Coming For Your Ride

Automotive Ethernet. It really is a thing. Our cars will have to outsmart our phones if we’re going to hand over the reins in any meaningful (and safe!) way. Data transport around the car of today takes a number of forms. My recent rental was a rolling WIFI hotspot with a Bluetooth pairing feature for the infotainment. Naturally, there were good old USB ports scattered around the big black Chevy where the ashtrays used to go. And don’t forget the GPS system. We can either interact with a machine that knew the area or simply push GM’s OnStar button so that a real person can look it up for us.

That was just the customer interfaces aside from normal car-driving stuff. In the end, I relied on my phone for directions and the generic fleet-vehicle familiarity to get around South Florida. The phone has the edge for the moment. The fate of the Impala is gloomy indeed but new things are on the horizon. Nobody wants to be caught not reaching for the brass ring. Ethernet is one of the means to that end.

 

What is Ethernet?

From a physical standpoint, ethernet is a serial port. A connector and a few wires. It is comparable to later versions of USB in that regard. The automotive industry has a similar standard called CAN-Bus. It grew up with the sector as the low-speed and fault-tolerant pairs of twisted wires running from end to end with breakouts as required. At 120 ohm differential, the CAN-Bus goes a little higher in impedance than we usually see.

 

Image credit:Author

 

The physical architecture hardens for the 100 MPH test.  All along, new ways of moving data down the pipe are invented in the Media Access Control (MAC) sub-layer. Depending on who you ask, it could also stand for Medium Access Control. In the “stack”, the MAC sits right above the PHY layer. That’s us. These two layers form the base of the stack and are what all of those IEEE 802.3-something documents attempt to define. As the lower half of the Data Link Layer, the MAC is a close cousin of the Logical Link Control (LLC) sub-layer.

“Standard” Operation

The point of these standards is coming up with agreeable details about the form of the bit stream. Basically, we’re framing the data in terms of how many bits are sent at a time, how to account for them at the receiving end and what to do about corrupted data once detected. The frame accounts for stop bits, parity, and duplexing as agreement. I’ve been around for a while and recall the same type of settings for my 1200 baud modem back in the day. Those attributes are universal.


The standards also establish a hierarchy of what type of data gets priority in case of a timing clash. Overloading the inputs of the vehicle’s Electronic Control Units that form the central nervous system is always a concern. The 8-bit systems of simpler times gave way to 16-bit and so on up the binary chain.

Sort it out in at the Software/Hardware Boundary


The standard Media Independent Interface (MII) is the baseline and uses 16 pins. That was followed by a Reduced MII (6 or 10? pins) and a Gigabit MII and, naturally, Reduced Gigabit (RGMII). Then, there is Serial Gigabit Media Independent Interface and, finally, the 10 Gigabit XGMII where it is going back to lots of pins - for now. (XAUI, represent!)

 

Image Credit: Cambridge University

 

The evolution of the standards is mostly about these types of operating norms and, more data throughput each time around. Dropped packets or high bit error rates can often be traced to poor design on some level so it is useful for us to at least skim the surface of what happens on the test bench. I’m not a “full-stack” developer but this stuff sinks in a little at a time. The trend is always faster, more reliable, more secure, and more while maintaining backward compatibility.

It is that last thing, the compatibility, that is helping usher in a wave of Ethernet for Automotive technology. Over the years, the networking giants have seen their mandatory 10X improvements on the standard come along every so often. Adapting to those kinds of data rates was never a concern on the vehicle assembly line until now. Sensor fusion, turning many data streams into actionable information in real-time takes a big pipe. Just about every aspect of driving that can be analyzed has a sensor.

Data, Driven

Every second of operation involves a ton of data. The vehicle wants to know if all four tires are on the ground and rotating. It needs to know if you are at sea level or on a mountain pass so it can precisely regulate the air/fuel mixture. Raise your hand if you have had to pay for a new air-mass sensor. Ok, put it down. Should the car turn on the headlights or wipers? Ask the sensors. Should it warn you about the car in your blind spot? Sensor. Is it time to deploy the airbags? All of them? Now? How about now? Inquiring cars need to know.

 

That is all before we consider the creature comforts and infotainment systems. My car sniffs the air outside and switches the air conditioner to recirculate if it thinks I might not like the odor out there. It never ends. All of it is data-driven. The looming 5G roll-out will enable applications that are yet unthought of. Synching with that network will be easier if the data is from the same playbook. The security concerns are real as bad actors use more sophisticated hacking techniques. The Ethernet community has been fighting that fight all along.

The latest iteration of the standard for automotive Ethernet is IEEE's 802.3bw-2015. You may already be driving around in a Local Area Network on wheels. According to Teledyne LeCroy’s David Maliniak, Automotive Ethernet provides higher bandwidth data transmissions compared with LIN (19.2 kb/s), CAN FD (15 Mb/s), FlexRay (10 Mb/s), and MOST (25, 50, or 150 Mb/s shared).

 

Image credit: TE Connectivity

Vehicular Ethernet is manifested on the printed circuit board with the serialization of the data.  You are going to want to match the lengths on those lines and treat them as you would any high-speed network. A Clock and an MDIO line will be part of the bus along with the TX and RX. Don’t expect those connectors that snap in like a phone jack.

Motor vehicles are a different world from a data center. Chunky connectors are our thing. Meanwhile, Ethernet has used transformers at the connector before and it is no different here. The ADAS and entertainment systems in our vehicles will inevitably get better and hungrier for information. The pipelines will have to widen to accommodate all of this data. The Ethernet is coming. Lock and load your chunky little connectors.




 

 

 

About the Author

John Burkhert

John Burkhert Jr is a career PCB Designer experienced in Military, Telecom, Consumer Hardware and lately, the Automotive industry. Originally, an RF specialist -- compelled to flip the bit now and then to fill the need for high-speed digital design. John enjoys playing bass and racing bikes when he's not writing about or performing PCB layout. You can find John on LinkedIn.

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