RE: Using DLC or data byte count in frame in a CAN driver API

My personal preference would be to use the number of payload bytes rather
than the mapped DLC values. Otherwise, user application code would have to
make that conversion somewhere anyway with the increased risk of errors.
It's the driver writer's job to get it right.

I would also like to see a (runtime configurable) feature that allows for
automatically selecting the best matching payload buffer size when
transmitting data.
E.g. with this feature enabled, I could pass a buffer with an arbitrary size
up to 64 bytes to the driver and let the driver figure out which type of
frame to use (i.e. smallest one that can contain all the payload data).
Alternatively, when it is disabled I would only be able to pass a buffer
that matches one of the allowed sizes in CAN FD.

cheers,
Bram

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
Heinz-Jürgen Oertel
Sent: woensdag 6 februari 2013 21:23
To: [email protected]
Subject: [CANLIST] Using DLC or data byte count in frame in a CAN driver API


Hello,

currently some of us working already on integrating CAN FD in different CAN
device driver software.
In the past we had the Data Length Code DLC, which was a one to one
translation to the number of bytes in a CAN frame.
This was used in the API for receiving and transmitting CAN frames.

With CAN FD that is more tricky.
There is the following relationship:
    DLC     bytes
-------------------
	 0		 0
	 1		 1
	...
	 8		 8
	 9		12
	10		16
	11		20
	12		24
	13		32
	14		48
	15		64

The question is now:
- should we still use the DLC
  when exchanging data between user application and driver
- should we use a 'length' as number of bytes
- or both, (but who takes care that both fit together?)

Any suggestions and ideas are welcome.
May be some of you are later working with such kind of software.
It's on you to define the interface.

Regards
   Heinz

 



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