HL7692 PiloT

The aim is to configure the Raspberry Pi Raspian OS and the HL7692 to use the USB MBIM protocol to enable cellular communications between the Raspberry PI and the HL7692

HL7692 module AT command configuration

With network manager and associated helpers disabled it is possible to manually command / configure the HL7692 via it’s USB serial port

With network manager manger running it’s better to use the physical UART connection between the RPi and the PiloT / HL7692. This works ok on the RPi’s that don’t have WiFi or the RPi4.

To access the HL7692 USB serial port command interface use a serial terminal tool like minicom

$ sudo minicom -D /dev/ttyACM0

To access the physical serial port use something like this (look on line on how to enable the physical serial port) - this was used on the RPi4

$ sudo minicom -b 115200  -D /dev/ttyS0

LEDs

Note that the LED port configuration is erased if the modem firmware is updated

The PiloT board recommended settings are as follows - the modem should be preconfigured like this when the PiloT board is new

LED D6

Set LED D6 as cellular network status indicator with the following command

at+ksync=2,7

With this setting the LED D6 behaviour is as follows

1. LED PERMANENTLY OFF: Not registered / Initialization / Registration denied / no SIM card
2. LED 600 ms ON / 600ms OFF: Not registered but searching
3. LED 75 ms ON / 3s OFF: connected to the network

LED D5

Set LED D5 as the cellular PiloT module boot and power indicator

at+kgpio=8,1

With this setting the LED D5 behaviour is as follows

1. If the modem is off then the LED will be OFF
2. Following modem powered off - if a power on signal is applied to the PiloT module the LED should momentarily flash on
3. Then the LED will be OFF
4. After the modem has booted the LED should be ON

HL7692 USB port composition

Currently network manager manages the HL7692 network interface via MBIM if the HL7692 is reconfigured to USB composition 2 which gives 1 MBIM and 1 USB port. This a change from the modules default setting

Note that at the time of writing (August 2019) the Sierra AT command guide indicated that three USB serial ports will be made available. But this wasn’t the case with FW RHL769x.2.26 and RHL769x.2.27 one MBIM and one serial AT port is available

Configure the composition to enable and MBIM interface

AT+KUSBCOMP=2

Check the composition

AT+KUSBCOMP?
+KUSBCOMP: 2

HL7692 and power on signal

We recommend using the power ON / OFF scripts to ensure correct state of modem operation

• this will override the RPi’s GPIO default state which may not be a stable signal state

Debugging notes

Using the physical serial port between the Pi and PiloT can be useful during debug as the single USB serial port is managed by networkManager. If only the USB serial port is available stopping networkManager may be useful

Check radio access technology

AT+KSRAT?
9 == LTE first then GSM
5 == LTE Only

AT+CGDCONT= 1,"IPV4V6","payandgo.o2.co.uk",,,  

Windows

I also tested the HL7692 PiloT on a Windows 10 machine

On the windows machine to get the HL7692 to work I had to

• Lock the modem to LTE - AT+KSRAT=5
• Manually set the apn, username and password using the windows cellular GUI
• Manually configure the modems context 1 by using AT command AT+CGDCONT = 1,”IP”,”payandgo.o2.co.uk”,,,

Debugging aids

Using

nmcli monitor

Successful connection OP capture

O2 Pay and Go (Prepaid): connection profile changed
cdc-wdm0: using connection 'O2 Pay and Go (Prepaid)'
cdc-wdm0: connecting (prepare)
Networkmanager is now in the 'connecting' state
cdc-wdm0: connecting (need authentication)
cdc-wdm0: connecting (prepare)
cdc-wdm0: connecting (configuring)
cdc-wdm0: connecting (getting IP configuration)
cdc-wdm0: connecting (checking IP connectivity)
cdc-wdm0: connecting (starting secondary connections)
cdc-wdm0: connected
Networkmanager is now in the 'connected (local only)' state
Networkmanager is now in the 'connected (site only)' state
'O2 Pay and Go (Prepaid)' is now the primary connection
Networkmanager is now in the 'connected' state
Connectivity is now 'full'