Re: bad gsm connections

I tried to analyze log files from one card having problematic connection. First my set-up briefly:
1) Embedded Linux card behind Huawei E3131 modem connection + NM & MM.
2) Drivers: Option and huawei_cdc_ncm.
3) Connection monitor with following functionality:
- monitoring frequency 10 minutes
- monitoring task, 1..18 ping operations with 10s timeout (max 3 minutes for one task)
- if all the 18 ping operations fail = task fails => USB power lines are sequenced.
- any of 18 ping operations passes = task passes => wait to next task start.
- if 12 successive tasks fail (2 hours) => boot card.
4) Occasionally bandwidth or field limited conditions that get modem firmware crash and boot frequently/at any time. It is not quite sure what crashes, but usb device gets re-numerated over and over.

From logs it seems that:
- Usually connection recovers automatically.
- If it does not, power sequencing usually helps.
- However, some times it does not help. If the first sequencing fails helping, next 10 power breaks fail too and 12'th task boots the card. It shows from the logs that USB enumeration does not work anymore when power sequencing stops working, which suggests that either udev or most likely some kernel driver has crashed. However, no kernel crash logs are printed.

Connection seems recovering soon after booting.
This might come now to wrong forum, as kernel driver seems the most likely suspect. Please, feel free forwarding me to correct one (MM perhaps). Also feel free suggesting your choice of kernel driver I should reload to get this locked state released without booting.


2017-03-08 20:22 GMT+02:00 matti kaasinen <matti kaasinen gmail com>:

2017-03-07 20:11 GMT+02:00 Dan Williams <dcbw redhat com>:
> > That's the modem firmware crashing and restarting.  It then
> > reappears
> > to the kernel and gets re-enumerated, and usb_modeswitch does its
> > thing
> > and then eventually it comes back as a modem.  Which could be due
> > to
> > any number of issues.
> >
> But the first thing to check is whether the modem has enough power.
> > Laptops and embedded devices are sometimes unable to supply enough
> > power to the USB ports while the modem is connected.

I studied this today by breaking power lines from USB cable and feeding modem power lines directly from laboratory power. Huawei E3131 dongle was enclosed in metal box to damp field. Good power supply did not help. It turned out that modem did not recover from this error mode with power sequencing and not necessarily by booting Linux card. It required longer break and opening the chassis lid. Which made me suspect warming up. However, heating did not trigger this error mode if field was somewhat better. So, perhaps either E3131 firmware or kernel driver does not tolerate low fields. Perhaps switching between modes (e.g. edge/gprs) triggers the error. Anyhow, I could not figure out the reason.

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