Understanding log sequence of events to debug hangup?

[Aleksander Morgado]

Hey!

First I'd like to say what a great project!  I've got numerous customers
> using this now, and am impressed by the capabilities and breadth of support
> for modems.
>
> I've run into an issue with a customer who is using ModemManager with a
> u-blox modem, and we're seeing a hangup that is being reported after the
> roaming registration is complete on AT&T.  When we look at our mobile core,
> the modem appears to be connected and given an IP address, and the
> connection is still up when the hangup is being reported.
>
> I'm doing my best to interpret the logs, and they are very readable.  I do
> see the sequence of events leading up to the "<debug> [1588357729.967755]
> (ttyACM1) unexpected port hangup!" (in this particular log) but am not
> clear on how/why this is happening.  I'm assuming that maybe this is
> detected with a RTS/CTS indication?
>
>
Here are the relevant logs:

<debug> [1588357729.881386] (ttyACM1): --> 'AT+CGACT?<CR>'
<debug> [1588357729.967755] (ttyACM1) unexpected port hangup!
<debug> [1588357729.976456] (ttyACM1) forced to close port
<debug> [1588357729.981632] (ttyACM1) device open count is 0 (close)
<debug> [1588357729.988668] (ttyACM1) closing serial port...
<debug> [1588357730.008063] (ttyACM1) serial port closed
<warn>  [1588357730.018495] checking if connected failed: Couldn't check
current list of active PDP contexts: Serial port is now closed
<info>  [1588357730.024490] (tty/ttyACM0): released by device
'/sys/devices/platform/soc/2100000.aips-bus/2184200.usb/ci_hdrc.1/usb1/1-1'
<info>  [1588357730.034720] (tty/ttyACM1): released by device
'/sys/devices/platform/soc/2100000.aips-bus/2184200.usb/ci_hdrc.1/usb1/1-1'
<info>  [1588357730.050015] (tty/ttyACM2): released by device
'/sys/devices/platform/soc/2100000.aips-bus/2184200.usb/ci_hdrc.1/usb1/1-1'
<info>  [1588357730.076956] (tty/ttyACM3): released by device
'/sys/devices/platform/soc/2100000.aips-bus/2184200.usb/ci_hdrc.1/usb1/1-1'
<info>  [1588357730.093692] (tty/ttyACM4): released by device
'/sys/devices/platform/soc/2100000.aips-bus/2184200.usb/ci_hdrc.1/usb1/1-1'
<info>  [1588357730.108045] (tty/ttyACM5): released by device
'/sys/devices/platform/soc/2100000.aips-bus/2184200.usb/ci_hdrc.1/usb1/1-1'
<debug> [1588357730.115839] Removing empty device
'/sys/devices/platform/soc/2100000.aips-bus/2184200.usb/ci_hdrc.1/usb1/1-1'
<debug> [1588357730.125628] Removing from DBus bearer at
'/org/freedesktop/ModemManager1/Bearer/0'
<debug> [1588357730.133782] [device
/sys/devices/platform/soc/2100000.aips-bus/2184200.usb/ci_hdrc.1/usb1/1-1]
unexported modem from path '/org/freedesktop/ModemManager1/Modem/0'

The "released by device" messages shown above are due to the kernel
reporting that the ttyACM ports are being removed from the system.

I'm afraid this is the TOBY-R200 crashing and self-reseting itself. You'll
need to bring this issue to u-blox support so that they can tell you how to
capture modem traces and how to analyze them.

But I also see these messages just after the ones above:

<info>  [1588357731.601227] Caught signal, shutting down...
<debug> [1588357731.615674] Stopping connection in object manager server
<info>  [1588357731.633252] ModemManager is shut down
<info>  [1588357731.893688] ModemManager (version 1.8.0) starting in system
bus...

Are you manually restarting ModemManager for some reason once the modem is
removed from DBus? This looks like you have some trigger to do that
manually? You definitely don't need this.



> The customer is using a u-blox TOBY-R200 modem, and I do not see any
> u-blox modems listed on the Supported Devices / compatibility page:
> https://www.freedesktop.org/wiki/Software/ModemManager/SupportedDevices/
>
>
That list was done a very long time ago. If a modem is not reported in that
list, it doesn't mean we don't support it. :)

-- 
Aleksander
https://aleksander.es
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