Handling QSS unsolicited in power state transitions

[Aleksander Morgado]

On 01/08/17 10:04, Carlo Lobrano wrote:
> last week I was working to handle a behavior that most of the Telit modem
> have, that is, they emit *#QSS* unsolicited in consequence of *+CFUN*
> commands. Most of the times, the modems are already in *+CFUN=1* at the
> start so we did not notice it in a normal power up, but if we put the modem
> in power low state, the *+CFUN=4* triggers a *#QSS=0* that the ModemManager
> considers as a SIM swap. Note that this is receved as soon as the modem is
> enabled again, because currently we release SIM swap ports while disabling
> the modem, and, if we set power state on, ***together with the #QSS=1 due
> to +CFUN=1*** causing a crash.
> 

Aren't the sim hot swap unsolicited messages received always, regardless of whether the modem is enabled or disabled?

> Generally speaking this behavior isn't wrong per se (a part from the crash,
> that can be fixed), because the SIM is actually turned off, but in this
> configuration we cannot re-enable the modem, while sending a *+CFUN=1* the
> modem would be usable again.
> 
> So, I made a couple of patches, (1) avoid releasing SIM swap ports on modem
> disable, so we can still receive SIM notifications at the right moment, and
> (2) ignore QSS unsolicited when changing *+CFUN* state and only for a short
> amount of time. The problem is that there isn't a specific timeout within
> which this unsolicited must arrive and according to my tests it is quite
> variable (about between 3 and 10 seconds).
> 

The only issue is when getting #QSS=0 after a +CFUN=4, right? Because we would be getting a SIM removal event that isn't really such thing, it was just the SIM card being powered off as well. Is there maybe a command to get into low-power mode that shuts down RF but leaves SIM card powered?

> One solution is then to ignore *#QSS* for like 10 seconds, while the other
> one is to keep ignoring them in the whole time between *+CFUN=4* and*
> +CFUN=1*. This last solution is more consistent, but it won't let us get
> SIM removal/insertion when the modem is in power-state-low.

A wild idea, but would it be possible to wrap around the +CFUN calls between #QSS indication disabled and enabled?
E.g.
  Disable #QSS indications (not just ignore them in MM, but explicitly tell the modem to not send them)
  +CFUN=4
  Enable #QSS indications right away
  (maybe the #QSS won't arrive here as it was disabled during CFUN?)

Would that make sense? Or will the #QSS be sent anyway, even if it was disabled during the +CFUN being run?

-- 
Aleksander
https://aleksander.es