4 ms·

Interesting - never realized there would be multiple CAN buses in a car. That probably makes it a lot easier to not screw things up - if you know that the mediu

Interesting - never realized there would be multiple CAN buses in a car. That probably makes it a lot easier to not screw things up - if you know that the medium speed bus is only connected to non-safety-critical systems, then it's easier to trust that when you send out your hand-crafted CAN packets, you're not going to cause anything too drastic to happen.

muro 9y ago
You want to keep "unimportant" (think radio) away from "important" (drive train). Also, there are only so many IDs you can use.
- Silhouette 9y ago
  Unfortunately, the lines are increasingly blurred. The days when you could separate basic driving mechanics like steering, acceleration and braking from other controls, sensors and remote inputs are fast disappearing into history.
ThrowawayIP 9y ago
Security (or safety) is one reason for multiple CAN buses. Another is saturation of the bus (too many messages).
tyingq 9y ago
Not all automakers do this. There are vehicles where the obd-ii port has access to the main CAN bus.
mrpippy 9y ago
Indeed. Especially important when you remember that most of the (many!) devices in a car sitting on CAN buses come from outside suppliers, and black-box testing of these modules can only go so far to verify the CAN implementation and stability. AFAIK, Ford actually mandates that their suppliers use a standard CAN stack provided/licensed by Ford (FNOS, the Ford Network Operating System) to try and ensure a level of quality in implementations. It's a good idea, one I haven't heard of other automakers doing (although I'm not in the industry any more)
- duncan_bayne 9y ago
  My inner five year old hopes that FNOS was developed by the Ford Network Operating Research Division.
- throwawayzzz111 9y ago
  Yes, we need property testing of this stuff to become the norm. https://erlangcentral.org/videos/testing-automotive-software-with-erlang/ https://erlangcentral.org/videos/testing-automotive-software... http://www.cs.tufts.edu/~nr/cs257/archive/john-hughes/quviq-testing.pdf http://www.cs.tufts.edu/~nr/cs257/archive/john-hughes/quviq-...

muro 9y ago

You want to keep "unimportant" (think radio) away from "important" (drive train). Also, there are only so many IDs you can use.

Silhouette 9y ago
Unfortunately, the lines are increasingly blurred. The days when you could separate basic driving mechanics like steering, acceleration and braking from other controls, sensors and remote inputs are fast disappearing into history.

ThrowawayIP 9y ago

Security (or safety) is one reason for multiple CAN buses. Another is saturation of the bus (too many messages).

tyingq 9y ago

Not all automakers do this. There are vehicles where the obd-ii port has access to the main CAN bus.

mrpippy 9y ago

Indeed. Especially important when you remember that most of the (many!) devices in a car sitting on CAN buses come from outside suppliers, and black-box testing of these modules can only go so far to verify the CAN implementation and stability. AFAIK, Ford actually mandates that their suppliers use a standard CAN stack provided/licensed by Ford (FNOS, the Ford Network Operating System) to try and ensure a level of quality in implementations. It's a good idea, one I haven't heard of other automakers doing (although I'm not in the industry any more)

duncan_bayne 9y ago
My inner five year old hopes that FNOS was developed by the Ford Network Operating Research Division.
throwawayzzz111 9y ago
Yes, we need property testing of this stuff to become the norm. https://erlangcentral.org/videos/testing-automotive-software-with-erlang/ https://erlangcentral.org/videos/testing-automotive-software... http://www.cs.tufts.edu/~nr/cs257/archive/john-hughes/quviq-testing.pdf http://www.cs.tufts.edu/~nr/cs257/archive/john-hughes/quviq-...