sys/can: improve SJW calculation#21756
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Teufelchen1 merged 2 commits intoRIOT-OS:masterfrom Oct 7, 2025
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crasbe
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Type: enhancement
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Sep 30, 2025
sys/can/device.c
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| timing->sjw = SJW; | ||
| } | ||
| else { | ||
| if (!timing->sjw) { |
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To facilitate validation for any reader, it would be valuable to have the CIA paper reference here as a comment.
sys/can/device.c
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| timing->sjw = SJW; | ||
| } | ||
| else { | ||
| if (!timing->sjw) { |
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SJW must not be bigger than phase segments 1 and 2. If a value is provided, not probing for phase segment 2 would leave the possibility that sjw is larger than segment 2.
if (!timing->sjw) {
timing->sjw = timing->phase_seg2;
}
else {
timing->sjw = MIN(timing->sjw, timing->phase_seg2);
}
timing->sjw = MIN(timing->sjw, timing->phase_seg1);
timing->sjw = MIN(timing->sjw, timing_const->sjw_max);
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Thanks for the review.
I simplified it a bit further ( also including the no known max default) but avoid including some MIN definition and kept the comments
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sys/can/device.c
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| } | ||
|
|
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| if (timing->sjw > timing->phase_seg2) { | ||
| /* SJW shall not be bigger than phase segment 1 */ |
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Suggested change
| /* SJW shall not be bigger than phase segment 1 */ | |
| /* SJW shall not be bigger than phase segment 2 */ |
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I did not test it but you did, right @kfessel? If so, here is the ACK.
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Prove of Test Debug enable in device tests/drivers/candev/ BOARD=same54-xpro without sjw improvment with sjw improvment added line break to term for readability |
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Contribution description
SJW was defaulting to 2 -> good for 8MHz time quanta bad for higher clock
With this PR:
This should usually end up with SJW being the same as phase 2 for can configuration having the sample point at 87.5%) ->
it's starting at value of phase 2 making changes by the following comparisons unlikely.
Testing procedure
read
run can and see improved stability of connection for slightly drifting clocks on either end (less failed frames due to synchronization issues).
Issues/PRs references
http://www.oertel-halle.de/files/cia99paper.pdf might help under standing the sjw value