UART high speed hang fixed - disabled wkup_m3!!

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1

Hi all,

I have been having an issue where when heavily using a serial UART at high speed I would get a lot of overrun errors on the port and eventually the BBB would hang/appear to power off. It was very strange, we couldn’t get kernel debugging at all, it did appear that is had powered down.

This morning I was making some changes to a device tree (attached) and managed to fix the problem, by disabling the wkup_m3 the problem appears to have disappeared.

Usually it would happen after around 2-3 hours and so far have uptime of 12+ hours on 2 test units I have on the bench so it is looking good.

Now…why is this the case. UART 2 is the one heavily used and the baud rate is 3Mbps and we are pretty much saturating the link at times.

  • What exactly does the wkup_m3 do?

  • Is it safe to keep it disabled? (Older device trees didn’t seem to use it)

  • Where would this fault lie, hardware or software and who should I report it to?
    I’ve been pulling my hair out for a week and thankfully appear to have a solution!!!

Happy Thanksgiving all.

Lee

testOverlay.dts (1.36 KB)

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http://free-electrons.com/kerneldoc/latest/devicetree/bindings/remoteproc/wkup_m3_rproc.txt

From the gist of things it seems to be part of the PRU power management code in relation to remoteproc.

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Thanks William. If it is power related that would explain the end result potentially.

Now to try and work out why! I don't think leaving it disabled is a bad thing.

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I was thinking that a possibility is that they’re both peripherals, or device modules connected via the L4 interconnect. The PRU is for sure, and I would also think the UARTs sit on the L4 interconnect as well. Maybe I’m wrong.

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Yes that might make sense there, I’ve just looked at the docs myself.

Weird behaviour though!