[cyberax]

Tesla really deserves some kudos for pushing the 48V architecture and the Ethernet-based communication. It drastically simplifies the wiring mess that is in a typical car.

And it's not even close. Just watch the teardown of Cybertruck and compare its wiring to something like F150.

[throw0101d]

> Tesla really deserves some kudos for pushing the 48V architecture and the Ethernet-based communication.

For the record, 42V systems were experimented with in the 1990s:

* https://en.wikipedia.org/wiki/42-volt_electrical_system

In the 2011 German automakers agreed to 48V as the next step after 12V:

* https://en.wikipedia.org/wiki/48-volt_electrical_system

BMW was the first the first with Ethernet:

* https://www.marvell.com/blogs/the-right-stuff-a-past-and-fut...

[cyberax]

This has been a real head-scratcher for me. BMW and other automakers could have vastly improved their cars by switching to 48V a decade ago, but they still keep just plodding along with 12V.

I have no explanation for this.

[m463]

I think it's like any existing vs new tradeoff.

Tesla didn't have any existing, so their clean-slate math was clearly in favor of 100% new technology.

(Well, they did have 12v existing in their other cars, but they were clean-slate in the truck.)

[phlipski]

It's a classic chicken and egg economic problem. BMW doesn't make the chips/electronics that support the 48V architecture - Bosch & Continental (with NXP/TI/Infineon/Renesas as their silicon suppliers) do and they're not going to support 48V unless ALL (or a significant majority) of the automakers will. So it's a game of chicken.

[maxerickson]

The semiconductors have been available for 20 years.

[michaelt]

Eh, yes and no.

I designed some stuff along these lines 15 years ago. At that time, 12 volt stuff was not just available, it was available with great economies of scale and a huge range of options, off the shelf. You need an automotive-qualified relay? A light? A solenoid? A DC-DC converter module? A fan? You'd have 100 choices at 12v, 30 choices at 24v and 3 choices at 48v.

[hulitu]

> automakers could have vastly improved their cars by switching to 48V a decade ago,

The microcontroller still runs at 5/3.3/1.8 V.

[numpad0]

care to define "improve"...?

[cyberax]

More robust, cheaper (far simpler wiring harness), eventually ability to do zonal assembly.

[numpad0]

Are BMW cars less reliable, expensive, not ready for zonal assembly...?

Major car components like doors or front axles are assembled in parallel to miscellaneous parts on the main body, and all .join() at the final assembly. This had been the case for past 30-50 years, possibly more, in case this needs to be said.

[cyberax]

They can be even more reliable. And they definitely _are_ expensive.

> Major car components like doors or front axles are assembled in parallel

And doors (and tailgates) are the biggest body component that is _sometimes_ assembled independently. Then workers manually route cables through the body.

Pre-routing cables inside panels that can then just be welded together can save a lot of labor.

[theshrike79]

Tradition, long supply chains etc.

Tooling all their shit to 48V is a massive undertaking with pretty much zero advantages.

[cyberax]

They don't need to retool all the factories at once. They could have gradually introduced 48V systems in parallel with 12V, slowly phasing in new components as they replaced the old 12V.

[typewithrhythm]

Converting between voltages is not a free action, and running two systems is more complicated than one...

You really need some special component that is much better at 48 for it to be worth it, otherwise a delayed platform switch is better; one some competitors have moved and the suppliers exist.

[cyberax]

Starter motor, power steering, heated seats, powerful headlights, power-hungry onboard computers.

They _all_ benefit from 48V.

[Kirby64]

The special component was supposed to be the starter. With start stop systems essentially mandatory, the starter runs much much more often and therefore wiring savings on the starter are pretty useful…

[vardump]

Less copper in the car is not a "zero advantage". Cheaper and lighter.

[iknowstuff]

none of them actually shipped a mass market almost exclusively 48V product if you’re trying to imply tesla’s push isnt as massive as it is.

[MuffinFlavored]

> BMW was the first the first with Ethernet:

BMW ENET is non-standard, DoIP is standard. :)

[jeffbee]

How about comparing it to a teardown of a Rivian? Rivian uses 2-wire ethernet but 12V, so it seems like a more interesting comparison.

That said, it all seems like inside baseball to me. The BMW 850i pioneered the CAN bus, but that car was forgettable and although CAN bus took over the car industry that did not seem to create any durable advantages for BMW.

Ethernet seems like the inevitable replacement for CAN, in light of VW's investment in Rivian, and 48V vs. 12V for the low-voltage systems seems like a wash.

[hulitu]

> Tesla really deserves some kudos for pushing the 48V architecture and the Ethernet-based communication.

And some schooling. They shall learn about pokayoke.

[outworlder]

We can simplify the wire mess today by using more CAN bus devices.

What is ethernet bringing to the picture?

[cyberax]

CAN is slow. At best it's around 1Mbit, but you get into electrical limitations. So you have to run multiple CAN buses in parallel and carefully manage bandwidth limitations.

My Chevy Volt had 4 different CAN buses and one additional LIN bus.

This can all be replaced with just two Ethernet buses: for safety-critical and non-critical uses. And the gigabit speed provides plenty of bandwidth for any reasonable sensor traffic, even including camera feeds.

The current architecture was justified in 90-s when LIN PHYs were an order of magnitude cheaper than even CAN PHYs. Now Gigabit Ethernet PHYs cost less than a dollar.

[eschneider]

It's unlikely that the multiple CAN buses are being used to increase speed by, say multiplexing them. In general, vehicles use multiple CAN buses for enhanced security. For example: things like diagnostic ports are often on their own CAN buses so data can't be directly injected into onboard systems.

[cyberax]

All but one CAN bus in my Volt were connected to the OBD port. The unconnected bus controlled the high-voltage battery contactors and some other critical stuff.

The "main" bus was saturated with data, more than 80% of bandwidth utilization at 512kbs. And it kinda had a mix of everything, from street names to be displayed on the dashboard to ECU messages. The other two buses had some random messages, with no rhyme or reason for the split ( https://vehicle-reverse-engineering.fandom.com/wiki/GM_Volt ).

[KK7NIL]

> What is ethernet bringing to the picture?

Over 3 orders of magnitude faster datarates.

CAN FD: up to 5Mb/s

Automotive Ethernet: up to 10 Gb/s

[gregoriol]

Why would you need 10 Gb/s speeds in a car

[nunez]

FSD will benefit from high-resolution (4K or above) camera feeds (for things like reading signs and detecting small obstacles). You can do this in a 10Gbps network and have tons of headroom for every other function the car will perform.

[the_mitsuhiko]

Why would you not? Tesla is sending even the infortainment data stream through that bus. It's incredibly helpful having all data travel on a singular wire because you can tap in at one point and read it all out. Makes the entire system significantly easier to debug, understand and develop against.

[gregoriol]

And hack/steal, right?

[vardump]

10 Gb/s is not all that much for cameras. Enough for one 60 Hz 4k 14-bit depth camera transmitting raw bayer data.

60 Hz * 3840 * 2160 * 14bit is 6.96 Gbps.

[dpeckett]

It's a good thing we invented video compression and hardware codecs/encoders a long time ago.

What you'll actually be sending is a high bitrate mpeg stream, probably 54Mbps or thereabouts, you could probably fit 50x camera streams on a shared 10Gbps bus.

[bsder]

Larger packets and bandwidths.

Bandwidth: you can't ship backup camera video or entertainment system audio over CAN, for example.

CAN was meant for short, real-time packets. 8 bytes in initial configuration. CAN FD allows 64 byte packets.

You spend a LOT of protocol doing packet fragmentation and assembly using CAN--which then negates a lot of the real-time guarantees.

CAN should be used for the short safety critical stuff. Ethernet should be used for everything else.

[elcritch]

Ethernet can handle real time now even in bus configurations!

10BASE-T1S is a new standard geared for automotive. It uses physical layer collision avoidance instead of classic Ethernet exponential backoff. This provides deterministic maximum latency.

Though you can get max latency guarantees with switched Ethernet and the appropriate switch QoS and hardware.

[throw0101d]

> What is ethernet bringing to the picture?

More speed and zonal architecture:

* https://www.electronicdesign.com/markets/automotive/article/...

* https://www.bosch-mobility.com/en/solutions/control-units/zo...

[m463]

I'll bet a hidden factor here is development and testing.

They can probably develop for a car ethernet lan with a desktop pc and car "peripherals".

Not that there aren't canbus cards for pcs, but still.

[numpad0]

This sounds like the real answer. Replacing an automotive standard with Ethernet is going to reduce friction onboarding junior webdevs with MacBooks, and enable a more stable higher turnover labor intensive organization.

[maxerickson]

CAN to PC adapters are a few hundred dollars, it isn't causing much friction.

[m463]

With ethernet you can probably run the car software in containers.

I can imagine a container to simulate each hardware unit, a small inter-contaner lan, and develop code that way.

[dpeckett]

You can already do this trivially with Linux vcan[1] so I don't buy this argument.

I think the bigger factor is that innovation in the CAN ecosystem has been lagging behind Ethernet for decades now. Only reason it's had such staying power is industry inertia.

1. https://netmodule-linux.readthedocs.io/en/latest/howto/can.h...

[soco]

Reminds me when my Opel resetted itself while driving on the highway. Oh, the adrenaline...

[the_mitsuhiko]

Central bus instead of many point to point connections. Look at how much fewer cabling the cybertruck has.

[rcxdude]

CAN is also a bus, that's not really a point in favor of ethernet.

[elcritch]

Ethernet can do both bus and switched. High speed switches enables a lot of architecture not easily enabled by CAN.

[JoshTriplett]

CAN has desirable electrical properties (e.g. hardware-level prioritization) if you have life-critical devices and non-life-critical devices on the same network. But it's painful to deal with from a software point of view, compared to IP-based protocols, for anything that doesn't require the properties of CAN.

[cyberax]

Industrial Ethernet (PROFINET) also has priorities and bandwidth reservation: https://en.wikipedia.org/wiki/Profinet#Technology_of_Class_C...

[aeternum]

Bitrate and max devices for CAN are limited.

[mulmen]

Bandwidth?

[saturn8601]

You'll be sorry when this move further hamper repair efforts and the TCO of owning a vehicle goes up.

[porphyra]

You can say that about any new standard. With that logic we'd all be stuck with knob and tube wiring.

[ElevenLathe]

Did cars ever use knob and tube?

[porphyra]

Not that I know of --- it's a figure of speech to compare it to an standardized method of electrical wiring in buildings that eventually got replaced with better standards despite similar concerns at the time.

[bluGill]

Well technically a spark plug is the tube part.