This is an example based on mbed-os
cellular APIs that demonstrates a TCP or UDP echo transaction with a public echo server.
This particular cellular application uses a cellular network and network-socket APIs that are part of mbed-os
.
The program uses a cellular modem driver using an external IP stack (LWIP) standard 3GPP AT 27.007 AT commands to setup the cellular modem and registers to the network.
After registration, the driver opens a point-to-point protocol (PPP) pipe using LWIP with the cellular modem and connects to internet. This driver currently supports UART data connection type only between your cellular modem and MCU.
For more information on Arm Mbed OS cellular APIs and porting guide, please visit the Mbed OS cellular API and contributing documentation.
$ mbed import mbed-os-example-cellular
$ cd mbed-os-example-cellular
#OR
$ git clone [email protected]:ARMmbed/mbed-os-example-cellular.git
$ cd mbed-os-example-cellular
See the file mbed_app.json
in the root directory of your application. This file contains all the user specific configurations your application needs. Provide the pin code for your SIM card, as well as any APN settings if needed. For example:
"nsapi.default-cellular-plmn": 0,
"nsapi.default-cellular-sim-pin": "\"1234\"",
"nsapi.default-cellular-apn": 0,
"nsapi.default-cellular-username": 0,
"nsapi.default-cellular-password": 0
You can choose which socket type the application should use; however, please note that TCP is a more reliable transmission protocol. For example:
"sock-type": "TCP",
If you like details and wish to know about all the AT interactions between the modem and your driver, turn on the modem AT echo trace.
"cellular.debug-at": true
If you like to add more traces or follow the current ones you can turn traces on by changing mbed-trace.enable
in mbed_app.json
"*": {
"mbed-trace.enable": true,
After you have defined mbed-trace.enable: true
, you can set trace levels by changing value in trace-level
"help": "Options are TRACE_LEVEL_ERROR,TRACE_LEVEL_WARN,TRACE_LEVEL_INFO,TRACE_LEVEL_DEBUG",
"macro_name": "MBED_TRACE_MAX_LEVEL",
"value": "TRACE_LEVEL_INFO"
}
The cellular modem driver in this example uses PPP with an Mbed-supported external IP stack. It supports targets when modem exists on the Mbed Enabled target as opposed to plug-in modules (shields). For more details, please see our Mbed OS cellular documentation.
Currently supported boards with onboard modem chips are:
u-blox C027 MultiTech MTS Dragonfly
The master branch is for daily development and it uses the latest mbed-os/master.
To use the latest stable version update to a Mbed OS release tag, for example:
mbed releases
* mbed-os-5.10.4
...
mbed update mbed-os-5.10.4
You may need to use --clean
option to discard your local changes (use with caution).
Use Mbed CLI commands to generate a binary for the application. For example, in the case of GCC, use the following command:
$ mbed compile -m YOUR_TARGET_WITH_MODEM -t GCC_ARM
Drag and drop the application binary from BUILD/YOUR_TARGET_WITH_MODEM/GCC_ARM/mbed-os-example-cellular.bin
to your Mbed Enabled target hardware, which appears as a USB device on your host machine.
Attach a serial console emulator of your choice (for example, PuTTY, Minicom or screen) to your USB device. Set the baudrate to 115200 bit/s, and reset your board by pressing the reset button.
You should see an output similar to this:
mbed-os-example-cellular
Establishing connection ......
Connection Established.
TCP: connected with echo.mbedcloudtesting.com server
TCP: Sent 4 Bytes to echo.mbedcloudtesting.com
Received from echo server 4 Bytes
Success. Exiting
- Make sure the fields
sim-pin-code
,apn
,username
andpassword
from thembed_app.json
file are filled in correctly. The correct values should appear in the user manual of the board if using eSIM or in the details of the SIM card if using normal SIM. - Enable trace flag to have access to debug information
"mbed-trace.enable": true
. - Try both
TCP
andUDP
socket types. - Try both
"lwip.ppp-enabled": true
and"lwip.ppp-enabled": false
. - The modem may support only a fixed baud-rate, such as
"platform.default-serial-baud-rate": 9600
. - The modem and network may only support IPv6 in which case
"lwip.ipv6-enabled": true
shall be defined. - The SIM and modem must have compatible cellular technology (3G, 4G, NB-IoT, ...) supported and cellular network available.
If you have problems to get started with debugging, you can review the documentation for suggestions on what could be wrong and how to fix it.