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Unread 12-02-2016, 11:44
blturner blturner is offline
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nagging problem with CPU usage

Our robot drives fine and we are not getting any errors on the drivers station but the CPU is 80% disabled and bumps 100% while enabled. it's hard to read this on the drivers station graph.(Perhaps there is a better place?)
I have looked for untimed while loops and can't find any. I slowed down all of our periodic task loops and that does not seem to make any difference.
We have poor update rates while in debug mode. Sometimes the front panel displays will be as much as 3 seconds behind reality and can be choppy. That makes it hard to trouble shoot and tune our PID loops.

Rebooting everything helps but the problems come back.
When I check the vi timings it says that various CAN bus subVIs from the WPIlib are using a lot of milliseconds of processing time. The fact that we have not touched these VIs and that it seems to be reporting more milliseconds than have passed or even would be available makes me think the report is in error. I believe it was reporting about 5 minutes of CPU usage only about 30 seconds after we deployed the code.

We are running 4 Talon SRX controllers on the CAN bus. We have them on different IDs. I have not checked them for sticky errors. I don't know what firmware they are running. I can't see how that would effect the RoboRIO CPU usage, but I have been reading that is the pat answer to anything having to do with them. I will check next time the team meets.

What I don't know is what normal CPU usage would be for the default code. How fast should our drive loop be in periodic tasks? 10,20 or 40 ms? The drive loop is our biggest piece of code and it seems small.

Is this normal? Will it bite us at competition? We had that happen in the past.

Is it Wifi interference? We have tried 5ghz and ethernet connection but nothing seems conclusive. Of course we are cramped for time, so I don't want to spend a lot chasing something that is not really a problem. But if this is an indication of something terribly wrong then I can move the issue to the top of the list.

I can post our code, but I don't know if I should post all of it or just the VIs in question. Well here's the whole folder.
https://www.dropbox.com/sh/rbo96razt...JWglOHvMa?dl=0

Thanks,
Brian
 


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