CAN-FD support for UAVCAN?

[Doug Bernauer]

CAN-FD is starting to gain wide adoption in the automotive industry.  It uses a low line speed for arbitration, and switches to a higher speed mid-packet to pass the data along at a very rapid rate.  It also allows for up to 64byte payload which is a huge throughput improvement as well.  The hardware is very mature at this point and is on most large microcontrollers and is starting to become available on smaller units.  

What it is: http://www.vector.com/portal/medien/cmc/events/commercial_events/VectorCongress_2012/VeCo12_8_NewBusSystems_3_Lindenkreuz_Lecture.pdf

How it works: http://uavcan.org/Core_design_goals

Of course, similarly to CAN it doesn't define any higher level protocols, which is where something like UAVCAN could be helpful.  Any ideas about providing CAN-FD support for UAVCAN?

[Pavel Kirienko]

Hi Doug,

I am aware of CAN-FD, and I agree that sooner or later it should be supported by the transport layer of UAVCAN. However, I don't think the support will be implemented in the first release of UAVCAN specification, because CAN-FD is nearly nonexistent yet on the modern UAV flight hardware, hence any proposed implementation will be hard to test and validate against real applications.

Despite the above, if you (or anybody else) have some ideas or propositions how UAVCAN could employ CAN-FD, you're welcome to share them here.

Pavel.

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[Scott Dixon]

Any further thoughts on CAN-FD support now that it's 2018 (almost ;-) ?

[Pavel Kirienko]

Scott,

CAN FD enabled hardware took a bit longer to appear than I expected. I have a working draft that should be published early next year. There is going to be an announcement first, here on this list and in the chat room at https://gitter.im/UAVCAN/general.

Pavel.

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[Scott Dixon]

Super excited to hear this and anxiously awaiting details. Can you provide a spoiler and let me know the scope of changes for the new specification? Are the differences limited to the transport protocol? Are service calls different? Will any of the datatypes change? Any hints would be helpful. Thanks.

[Pavel Kirienko]

Scott,

This change will only affect the transport protocol. All of the high-level logic was designed with CAN FD in mind from the first draft of the specification.

Basically, CAN FD frames will have the same format except for a single byte at the end stating the exact length of useful data in the frame (since the DLC field does not provide byte-level resolution). Quite straightforward. The challenge is to harmonize this properly with the DSDL compatibility concept proposed by Kjetil Kjeka (https://github.com/UAVCAN/dsdl/issues/36).

Pavel.

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[Nathan Friendly]

Hi Pavel,

Do you have any updates you can share on progress to support CAN FD in UAVCAN? 

Nathan

[Pavel Kirienko]

Still no progress. Too much other stuff to handle. I'm going to announce when there's something to look at.

Pavel.

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