Controlling the Automotive Network – CAN and TSN Update

Cars are hotbeds of systems innovation. I’ve been fortunate to be asked to write about many of these areas, from the MEMS underlying sensors to ISPs and radars, intelligent imaging and sensor fusion. And many aspects of design for safety within the SoCs around a car. But I haven’t written much about the networks connecting these devices. One piece back in 2017 was very informative for me at least. After talking to Nikos Zervas CEO at CAST plus some further research, I have an update.

A Babel of technologies

Automakers are eager to advance but they’re also conservative. Protocols I wrote about in that earlier blog are still very much around, judging by product offerings from companies like NXP and Renesas. LIN – a low-cost single wire technology to control windows, door locks, mirrors and power seats. Then there’s CAN – primarily for powertrain functions, and now CAN is advancing to CAN-FD supporting 5-8Mbps. And CAN-XL up to 10Mbps. All fully interoperable.

FlexRay is still very much around, touted as the deterministic technology required for safety guarantees in critical systems like airbags and ABS. Some suggest FlexRay as an eventual replacement for LIN and CAN, though at present cost is a barrier. Automakers seem content to stick with all three technologies for now.

I can’t find mention of MOST in a quick check of recent product literature so I’m assuming all the advances in multimedia and other high bandwidth traffic are moving to automotive Ethernet.

What is automotive Ethernet?

Ethernet is such a well-established technology that it might seem strange that it didn’t migrate to our cars long ago. It did – to on-board diagnostics and audio/video support – but not to safety and information-related functions. The reason is lack of deterministic latency. We may tolerate buffering on our phones and TVs, but there’s no room for delay in detecting a potential collision and not much more for a delayed direction update from the nav. To solve that problem, the IEEE 802.1 group formed a Time Sensitive Networking (TSN) group back in 2012. This organization has spun a collection of sub-standards and profiles to address different needs, with a mandate to support scalability. TSN now includes a synchronization standard, multiple traffic shaping options, frame preemption for express traffic, frame replication to support redundancy and filtering/policing options. You can watch an informative video HERE.

You may know that in network architecture automakers are moving towards a domain-based concept. Instead of proliferating MCU controllers around different functions they will be grouped into domains – Body, Chassis and Powertrain – to reduce costs and power. Over time, the expectation is that grouping will move more towards physical zones in the car no doubt for further performance, cost and power management. That may drive further consolidation in protocols, with Ethernet/TSN a strong candidate.

Who builds these interface solutions?

Today at least, US and European OEMs and Tier1s are driving TSN, with Korea and China following. I know the German automakers are involved, as is Bosch and certainly European and Japanese semiconductor makers. Where do they get IP if they want integrated solutions? CAN, developed by Bosch, now stands at CAN 2.0. CAN-FD is a later extension of that standard, as is CAN-XL. Bosch unsurprisingly supplies IP for these standards. So does CAST, with now more than 150 customers for their CAN cores.

That’s an interesting story. CAST develop a lot of their own IP but they also work with a few partners, one of which is Fraunhofer IPMS in Dresden. Fraunhofer is a highly respected application-oriented research lab with nearly 27,000 employees. IPMS is involved in all the standards committees, well plugged into the explicit and implicit requirements that go with these things. IPMS develop the cores and CAST productize for the IP market.

Which means also working with a verification partner – Avery Design Systems – to develop and jointly cross-check IP against VIP through development. Nikos says these solutions are sufficiently polished now that, unlike many IP/VIP mixes, an OEM can bring both up in their testbench in a day with that proven VIP solution, also available directly through CAST.

So far, that’s it for CAN-* IP providers – Bosch and CAST. Good for CAST! And when TSN started attracting interest, they worked with IPMS to develop that also, now in production for 4 years. They were one of the first providers to come out with a solution. Naturally all these cores offer functional safety options and the CAN cores are ASIL-B ready; the TSN IP will achieve that approval soon. You should check out both CAST and Avery Design Systems for their automotive connectivity solutions.

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