Re: bad gsm connections

[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.