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Welcome Dr Ken Tindell of Canis Labs
- Ken heard episode #631 where Chris was talking about a Noisy Rude Bus and he objected. Stringently (it seems Ken has since pulled down the posts, but they were in good fun)
- Chris had been planning to talk about Ken’s recent awesome post about CAN hacking and cars being stolen, so he asked Ken to be on the show!
- CAN was invented to reduce weight in car cable harnesses, which were increasing rapidly with more electrical features being included.
- CAN vs LIN
- CAN was expensive, but LIN is cheap because it’s bit banging the protocol from a microcontroller
- There are bridges to go between CAN and LIN buses.
- Modern cars have 20-100 ECUs (controllers), but it depends on the features the car has. But that’s not just microcontrollers, Ken estimates that could be as high as 700.
- Chris and Ken both had dealth with Philips / Freescale / NXP / Motorola as silicon vendors in the automotive space
- How does a tiny microcontroller get data onto the bus?
- Prioritized traffic
- CAN indentifier field has priority baked in
- Bus works like a giant AND gate where the lowest address wins
- 11 bits
- How to unwind CAN traffic
- Packing signals into CAN frame
- Tools to reverse engineer
- Protocol decoder for sigrok
- CAN HG
- 250kb is slow
- CAN bus bandwidth
- There is Ethernet in cars now, especially with more and more cameras
- Bandwidth vs latency
- Addressing through a gateway
- Atomic broadcasts means you know that each device has processed it
- Protocol hacking
- Trucks aren’t OEM based so more vertically integrated
- SAE J1939 standard in trucks
- If say Toyota develops the CAN messages, DBC files decode everything.
- But manufacturers don’t publish them, so some car messages are reverse engineered
- Accessories bus
- Who has access to DBCs?
- Diagnostic systems
- OBD2
- CARB
- CAN is physical ISO 11898
- CAN XL has IP packets, so you can use wireshark
- Ken has written about wireshark
- CAN 2.0, CAN FD
- Devices on a bus are normally all bare metal or RTOS because of the timing requirements
- OSEK standard
- Embedded system abstraction
- Dealing with the magnitude of decisions making in the automotive industry
- Chris asked about whether self-driving will happen in 5 or 20 years? (ie. does he agree with Chris or Dave). It was the latter, sadly.
- Autonomic Cars podcast with Dr Phil Coopman
This episode was wonderful. At one point Dr. Tindell referred to 3rd party accessory manufactures having to hire a team to do reverse engineering of bus protocols to allow interoperability.
I used to do exactly that at a previous job! It is certainly a tedious task, but is also an excellent way to learn about how all this stuff works (and see the insane things the manufacturers sometimes do as a result of the supply chain constraints with ECU’s).
I had such a great time doing that job, so it was really cool to hear about all this familiar stuff in addition to learning a whole bunch of new things.
Keep up the good work!