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

[Dan Williams]

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

> 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
> 
> 
> _______________________________________________
> ModemManager-devel mailing list
> ModemManager-devel at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/modemmanager-devel