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

The Amp Hour Electronics Podcast

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