Newest Firmware on RoboRio2 Causing Can Utilization to Oscillate and Spike to 100

[dumpsters]

We have 17 falcon 500s, 4 CanCoders, Rev PDH(2021), and REV PCM (2021), RoboRio2 using v4 software using c++, and an MK4 8 falcon swerve.

Some tests/ data we did of the can using roboRio2 with latest firmware(each % is the max value we saw):

1 falcon on can: ~7% utilization, however it was still oscillating and when we filmed the utilization on driver station in slow mo, we saw the % spike to 17% !

2 different swerve units w/o cancoder: ~32 max% (same oscillating behavior)

everything BUT drive base (excluding: 8 falcon 500s and 4 canCoders): 56 max% for just 9 motors! (same oscillating behavior)

Again, this was all with a blank code file.

Since CAN works when Motors are powered off, i started pulling breakers to see if somehow there was EM interference somewhere but no change - just a linear decrease in utilization when devices were cut off power. However, still oscillating usage that matched our tests above.

After seeing this troubling data we tried a robo rio 1 with older firmware and got a promising result where we saw 76% utilization for the entire robot and no crazy oscillation to 100%. Unfortunately the regulations require the newest firmware:

Rule update 8:
(https://firstfrc.blob.core.windows.net/frc2022/Manual/TeamUpdates/TeamUpdates-combined.pdf)

so we updated the roboRio 1 hoping it was somehow a roboRio2 issue. But after updating - the roboRio1 also got the oscillating, high can utilization…We made sure our REV firmware and ctre devices were up to date and still no change.

At this point - I feel like we’ve figured out that all the devices are contributing to this high utilization due to the newest firmware. They are all in this spiky behavior of oscillating between a reasonable can usage to a high can usage. 

Is there anything we are missing here or different software options to limit the information sent on the CAN? 

Thanks.

[sciencewhiz · Accepted solution]

The noise on CAN bus utilization is a reporting issue. See https://docs.wpilib.org/en/stable/docs/yearly-overview/known-issues.html#can-bus-utilization-is-nois...

Have you reviewed CTRE's documentation? They describe the timing of the different CAN messages and how to change them.