Howto "AT^SXRAT" (Cinterion specific)

[Giacinto Cifelli]

Hi Norbert, Aleksander,

>
> Giacinto, added you in CC, in case you have some suggestion.

don't worry, I am following MM, libMbim, libQmi.

>
> >
> > We're using a Cinterion ELS61-E R2 and seem to suffer from a lot of
> > "packet data disconnects" and cell/rat/MO switching.

Are you using the bare modem or on some datacard?
Is the power supply good?
And the antenna?
Please ask your contact in Thales (or a reseller) if there is a more
recent FW for your modem.  (I am part of Thales, too, but I am not
deep into ELS61 and all its variants and options, so it would take
more time to me to find out than for a more direct contact).

These would be the main things to look at, to understand and fix the
root cause, the rest below (in  which I am going to comment anyway),
could be workarounds for special situations, but not the solution.

> > We're advised to force the modem to use 3G/2G (or 4G/2G) Radio Access
> > Technology with the AT^SXRAT command.

MM doesn't use (as of today) this command, so you are guaranteed that
the modem will remember the settings.
AT^SXRAT allows to set up to 3 preferences, which can also be
combined.  I haven't tested on ELS61, but PLS62 should be the same.

> > We've been told the "AT+COPS=0" may reset SXRAT settings.

I have checked on the ATC, and indeed AT+COPS=,,,x (or AT+COPS=0) will
change the preferences, as well as AT^SXRAT, and the last-sent will
define the behavior.

> >
> > I've tried to do this via:
> > mmcli -m 0 --set-allowed-modes='2g|4g' --set-preferred-mode='4g'
> >
> > but it doesn't work and even if it would, I'm not sure this means the
> > "AT^SXRAT" command alwaysf ollows "AT+COPS=0" nicely.
> >
> > I see no "AT^SXRAT" in the source code, so I guess "AT^SXRAT" is a
> > Cinterion specific command that isn't supported yet.
> >
> > I do like to use the "AT^SXRAT" command.
> >
> > So I'd like to do a "AT^SXRAT" after each "AT+COPS=0". This involves
> > changing modem_3gpp_register_in_network, is this the right thing to do?
> >
> > If not, how to best use the "AT^SXRAT" command?
> >
>
> The Cinterion plugin currently uses AT+COPS also to configure access
> technology; e.g. if 4G-only is requested, we would run AT+COPS=,,,7
>
> Does this COPS based logic to configure access tech not work in the
> ELS61? Is ^SXRAT the only way to do that in the ELS61? If ^SXRAT is
> the only way to do it, we could upgrade the Cinterion plugin to use
> it. But I'm not sure that sending the SXRAT after each COPS would make
> much sense; is there no other way to do that?
>
> Also, if COPS=0 resets the desired access tech, I wonder if the same
> is currently happening with our already available COPS based access
> tech selection logic.

AT^SXRAT could be used for Intel chipsets (ELS61, PLS62, ...), instead
of the AT^SCFG="Radio/Band..." commands and/or AT+COPS=,,,x (and so in
the --set-allowed-modes command)
However AT+COPS=0 might be sent at startup if the modem reports +COPS:
2, and in this case it will start the registration/attach, but also
reset the preferred technologies.

I don't really agree to append AT^SXRAT to AT+COPS, that would make
the modem search twice in most of the cases, and I know that it is
particularly slow on this chipset under some conditions.
And so it would maybe solve a specific problem, but introduce others.

If you want a single tech, a better solution would be to track that in
the code where AT+COPS=0 is sent and use AT+COPS=0,,,x instead.

Best Regards,
Giacinto