EM7421 multiple AT command chanel?

IoT Modules MC/EM Series
1

Hello there,

I’m facing issue when I want to send at commend on the EM7421 after etablshing a internet connection.

• cdc-wdm0(qmi)
• ttyUSB0(qcdm)
• ttyUSB1(gps)
• ttyUSB2(at)
• wwan0(net)

I’m able to connect to internet using /dev/ttyUSB2 with ppp connection
I’m able to connecto to internet using ModemManager over • cdc-wdm0

I’m able to send AT command over /dev/ttyUSB2

But as soon I’m connected to internet with ModemManager / ttyUSB2, I’m not able to send AT command (receiving message sending sms etc…)

What Can I do ?

2

Establishing data channel using PPP is not recommended.

You can change to use MBIM in AT!USBCOMP.

For example, below are some steps to use MBIM in Ubuntu 18:

  1. sudo apt-get install libmbim-utils
  2. Modify /etc/mbim-network.conf to include APN/username/password of SIM card
  3. sudo mbim-network /dev/cdc-wdm0 start
  4. sudo dhclient wwan0
  5. “ifconfig wwan0” should show IP address
  6. ping 8.8.8.8 -I wwan0

Below is the log for your reference:

owner@CNHKG-EX-001367:~/legato/workspace/git/mangOH_2-7-2019$ cat /etc/mbim-network.conf 
APN=hkcsl
APN_USER=
APN_PASS=
APN_AUTH=
PROXY=yes

owner@CNHKG-EX-001367:~/legato/workspace/git/mangOH_2-7-2019$sudo mbim-network /dev/cdc-wdm0 start
Loading profile...
    APN: hkcsl
Querying subscriber ready status 'mbimcli -d /dev/cdc-wdm0 --query-subscriber-ready-status --no-close'...
[/dev/cdc-wdm0] Subscriber ready status retrieved: Ready state: 'initialized' Subscriber ID: '454003074155184' SIM ICCID: '8985200012741551847' Ready info: 'unknown' Telephone numbers: (0) 'unknown' [/dev/cdc-wdm0] Session not closed: TRID: '3'
Saving state... (TRID: 3)
Querying registration state 'mbimcli -d /dev/cdc-wdm0 --query-registration-state --no-open=3 --no-close'...
[/dev/cdc-wdm0] Registration status: Network error: 'unknown' Register state: 'home' Register mode: 'automatic' Available data classes: 'lte' Current cellular class: 'gsm' Provider ID: '45400' Provider name: '1O1O' Roaming text: 'unknown' Registration flags: 'unknown' [/dev/cdc-wdm0] Session not closed: TRID: '4'
Saving state... (TRID: 4)
Attaching to packet service with 'mbimcli -d /dev/cdc-wdm0 --attach-packet-service --no-open=4 --no-close'...
Saving state... (TRID: 5)
Starting network with 'mbimcli -d /dev/cdc-wdm0 --connect=hkcsl --no-open=5 --no-close'...
Network started successfully
Saving state... (TRID: 6)

You can also see here for other method to establish data channel:

3

Thanks for your answer !

Whats the difference between ModemManager and mbim-network ?

Seems that modemmanager is also unsing a net interface wwan0 ?

Whats the advantage of using ModemManager or mbim ?

Why it ’ s not recommended to use ppp connection ? I mean its working fine with same speed… isn’t it ?

4

officially there is no validation on PPP dial up as this is old technology
Protocol is not the same between PPP and MBIM, not sure if they really have same speed

Since you say that your modemanager is using AT command port to dial up, so it should generate an interface called ppp0.
you can double check in dmesg and see how the wwan0 is generated

5

AT!USBCOMP? seems to return me an error…

6

you need to unlock it first

AT!ENTERCND="A710"
AT!USBCOMP?
aT!USBCOMP=?
7

yes much better, thanks a lot for your support