The Amp Hour Electronics Podcast

#634 – The CAN bus can! with Dr Ken Tindell

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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
    • ...more
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