3 ms·

Why did you call out the CAN bus for water penetration? I thought it was an electrical specification and logical protocol, does it specify wires too?

boznz 3y ago
Correct neither CAN or Ethernet say anything about IP ratings, but I guess having an ethernet switch as a distribution rather than everything on a chain restricts the failure to one device.
- boznz 3y ago
  Just a thought but if its 48V and its ethernet I wonder if it is using power over ethernet?
  - grecy 3y ago
    I'm sure we will learn stuff like this when Munro tears one apart
- jaggederest 3y ago
  This is the same kind of failure you used to see in 10base5 and 10base2 networks, where one computer having a loose terminator could cause the entire LAN to be offline. With 10baseT (and I assume automotive ethernet) the bus is contained in the hub/switch/router instead of needing to be terminated (as in CAN bus, from my brief research anyway)
  - kalleboo 3y ago
    Although if you wanted to, I don't see why you couldn't build a CAN switch?
    - jaggederest 3y ago
      Definitely nothing stopping it, according to the wiki star architectures are supported, but I don't think many of the parts suppliers build them that way, would be my guess.
    - XorNot 3y ago
      I think the question would be why would you want to? At the point you're doing that, ethernet already exists including plenty of industrial specced hardware.
      - kalleboo 3y ago
        Presumably so you can reuse all of your existing CAN car parts. Even the lights are on CAN now, it's going to be a lot of stuff to transition to Ethernet. And you have thieves stealing cars by hacking into the easily-accessible car light CAN bus - a CAN network switch could also act as a firewall to fix those thefts without re-engineering every single part. It makes sense for Tesla since they're more vertically integrated but other car manufacturers seem more "parts bin" and having to migrate your whole car over to a new architecture will limit the parts you can use massively until the whole industry switches.
      - demondemidi 3y ago
        A few reasons: Ethernet electrical is more expensive and ethernet drivers are bigger code size then CAN, and more complex (buggier, you have a lot more buffers and way more state to manage with ethernet versus CAN). Plus CANFD can accommodate different frequencies, so cheaper hardware can participate on the same bus. This may change over time as larger cores are used (Renesas comes to mind) and bigger ethernet stacks that are already scrutinized can be shoehorned in.
liminalsunset 3y ago
In this particular case, it's because the CAN bus shares two wires across all devices, with everything connected in parallel. Water ingress or catastrophic failure to any of the wires, connectors, or terminations/devices can result in an open or short circuit, or at least enough load to cause the signal drivers to be incapable of driving the right levels. Although this particular example is from what some would consider a controversial video, this is an example of how water ingress can result in the disablement of vehicle electronics: https://youtu.be/Gio3DSTkQH4?feature=shared&t=181 https://youtu.be/Gio3DSTkQH4?feature=shared&t=181

boznz 3y ago

Correct neither CAN or Ethernet say anything about IP ratings, but I guess having an ethernet switch as a distribution rather than everything on a chain restricts the failure to one device.

boznz 3y ago
Just a thought but if its 48V and its ethernet I wonder if it is using power over ethernet?
- grecy 3y ago
  I'm sure we will learn stuff like this when Munro tears one apart
jaggederest 3y ago
This is the same kind of failure you used to see in 10base5 and 10base2 networks, where one computer having a loose terminator could cause the entire LAN to be offline. With 10baseT (and I assume automotive ethernet) the bus is contained in the hub/switch/router instead of needing to be terminated (as in CAN bus, from my brief research anyway)
- kalleboo 3y ago
  Although if you wanted to, I don't see why you couldn't build a CAN switch?
  - jaggederest 3y ago
    Definitely nothing stopping it, according to the wiki star architectures are supported, but I don't think many of the parts suppliers build them that way, would be my guess.
  - XorNot 3y ago
    I think the question would be why would you want to? At the point you're doing that, ethernet already exists including plenty of industrial specced hardware.
    - kalleboo 3y ago
      Presumably so you can reuse all of your existing CAN car parts. Even the lights are on CAN now, it's going to be a lot of stuff to transition to Ethernet. And you have thieves stealing cars by hacking into the easily-accessible car light CAN bus - a CAN network switch could also act as a firewall to fix those thefts without re-engineering every single part. It makes sense for Tesla since they're more vertically integrated but other car manufacturers seem more "parts bin" and having to migrate your whole car over to a new architecture will limit the parts you can use massively until the whole industry switches.
    - demondemidi 3y ago
      A few reasons: Ethernet electrical is more expensive and ethernet drivers are bigger code size then CAN, and more complex (buggier, you have a lot more buffers and way more state to manage with ethernet versus CAN). Plus CANFD can accommodate different frequencies, so cheaper hardware can participate on the same bus. This may change over time as larger cores are used (Renesas comes to mind) and bigger ethernet stacks that are already scrutinized can be shoehorned in.

liminalsunset 3y ago

In this particular case, it's because the CAN bus shares two wires across all devices, with everything connected in parallel. Water ingress or catastrophic failure to any of the wires, connectors, or terminations/devices can result in an open or short circuit, or at least enough load to cause the signal drivers to be incapable of driving the right levels. Although this particular example is from what some would consider a controversial video, this is an example of how water ingress can result in the disablement of vehicle electronics: https://youtu.be/Gio3DSTkQH4?feature=shared&t=181 https://youtu.be/Gio3DSTkQH4?feature=shared&t=181