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

[Dan Williams]

On Thu, 2018-04-05 at 18:32 +0000, Matthew Starr wrote:
> > -----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.

Are you enabling the modem from the scripts, or leaving that to
NetworkManager?  If you're leaving it to NM, you might try "mmcli -m 0
-e" before doing the sleep.

Dan

> 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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