u-blox TOBY-R200 Intermittent Long Registration on Simple Connect

[Matthew Starr]

> -----Original Message-----
> From: Dan Williams [mailto:dcbw at redhat.com]
> Sent: Thursday, April 05, 2018 1:22 PM
> To: Matthew Starr; modemmanager-devel at lists.freedesktop.org
> Subject: Re: u-blox TOBY-R200 Intermittent Long Registration on Simple
> Connect
> 
> On Tue, 2018-04-03 at 21:19 +0000, Matthew Starr wrote:
> > I have a u-blox TOBY-R200 running on an embedded Linux device with the
> > ModemManager 1.8-rc2 build, plus the patch for "ublox: fix 'any'
> > mode building".  On this device there seems to be an issue between the
> > automatic registration of the TOBY-R200 modem and ModemManager
> > reaching the Simple Connect State (5/8) Register.
> >
> > Between reboots I can get ModemManager to have a quick registration
> > and then have a slow (40 or more seconds) registration, where
> > ModemManager seems to have caught the modem right before it finished
> > auto registration or for some reason a denied state occurs and
> > restarts the entire registration over.  The issue seems to happen
> > right before simple connect state (5/8) Register is run.
> >
> > Here is what is reported during a quick registration step:
> > Simple connect state (5/8): Register
> > Already registered in network 'XXXXXX', automatic registration not
> > launched...
> >
> > Here is what is reported during a slow registration step:
> > Simple connect state (5/8): Register
> > Launching automatic network registration...
> >
> > See attached files for logs of the fast and slow registration from the
> > start of a simple connect to step (6/8) Bearer
> 
> In the quick case, the modem is already registered long before
> SimpleConnect gets to it's registration check.
> 
> In the slow case, the modem isn't yet registered.  It first reports
> GPRS=denied, UMTS=denied, LTE=idle.  MM then starts automatic
> registration on ACM0 and two seconds later gets GPRS=registered on ACM1.
> But ACM0 is still blocked running the AT+COPS=0 registration command
> which doesn't complete until 30 seconds later.  Only then can MM continue
> with the connection attempt, even though the modem was registered 28
> seconds before.
> 
> So yeah, it's (1) a race with modem firmware between the two cases, and
>  (2) the modem not returning from the AT+COPS=0 automatic registration
> request even when it has already registered.  (though there is perhaps
> another small race where if the modem has just registered the instant
> before MM sends AT+COPS=0 and hasn't yet notified MM, it will then do a
> full network scan and registration cycle when the +COPS=0 comes in)
> 
> How long has the modem been +CFUN=1 before you send the
> SimpleConnect() request?  Can you test whether waiting a couple seconds
> after the modem is fully enabled, before sending SimpleConnect(), makes a
> difference?
> We could also test-patch MM do that.  This isn't a real fix though...
> 
> Dan
> 

Dan,

I am using SystemV init scripts  for my init this device and I already tested putting in various sleeps right after starting ModemManager before I start NetworkManager which is setup to autoconnect to the cellular connection.  I put in a sleep as long as 30 seconds before NetworkManager is started and the rest of the boot continues and it made no difference.  I was still getting random results with sometimes MM seeing auto registration had already completed and other times it forcing a full registration.

Matt

> > Any idea on what the difference is between the fast and slow
> > registration and what might be causing it?  Any ideas how to fix it?
> >
> > Best regards,
> > Matthew Starr
> >
> >
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