[FS#115] WWAN-connections using 3g with HUAWEI ME909u-521 unstable

[LEDE Bugs]

A new Flyspray task has been opened.  Details are below. 

User who did this - Reiner Otto (reinerotto) 

Attached to Project - LEDE Project
Summary - WWAN-connections using 3g with HUAWEI ME909u-521 unstable
Task Type - Bug Report
Category - Base system
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - Medium
Priority - Very Low
Reported Version - Trunk
Due in Version - Undecided
Due Date - Undecided
Details - Actually, I am trying to stabilize wwan (3g actually; LTE later on) using pppd with my HUAWEI ME909u-521,
because either my MT7620-based router locks up during boot already; or after short period of real usage.
During night, when router is almost idle, just some watchdog date sent via wwan, no problem.

First trace of a possible problem was this msg in logread:
daemon.notice netifd: wwan (1676): Error setting WWAN mode!

Wich is expected, as in /lib/netifd/proto/3g.sh:

...
                        elif echo "$cardinfo" | grep -qi huawei; then
                                case "$service" in
                                        umts_only) CODE="14,2";;
                                        gprs_only) CODE="13,1";;
                                        *) CODE="2,2";;
                                esac
                                export MODE="AT^SYSCFG=${CODE},3FFFFFFF,2,4"    #####Will not work !!!!! Switching USB-Stick to 3g-preferred ?
...
...
                        [ -n "$MODE" ] && gcom -d "$device" -s /etc/gcom/setmode.gcom


Will not work, because the ME909u-521 rejects AT^SYSCFG . However, AT^SYSCFGEX will work, but having different syntax.
MODE="AT^SYSCFG=${CODE},3FFFFFFF,2,4" will be effective for simpler modems.

/etc/gcom/setmode.gcom returns exit 1; but this error is not checked in 3g.sh

Not shure, whether this is the reason for my problems; however, reason of concern, as high speed modems
are more and more common.
Willing to participate in testing/debugging. 

For details regarding my modem, consult 
HUAWEI ME909u-521 LTE LGA Module AT Command Interface Specification
http://www.paoli.cz/out/media/HUAWEI_ME909u-521_LTE_LGA_Module_AT_Command_Interface_Specification-V100R001_02.pdf




More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=115