AT Command Client

Overview

This sample demonstrates how to create an AT command client that bridges communication between the host console and a cellular modem. It uses the Zephyr modem subsystem with uart_pipe for console communication and modem_pipe for modem communication.

The sample provides a transparent bidirectional bridge:

Commands typed in the console are forwarded to the modem
Responses from the modem are displayed on the console
Supports AT command interaction and firmware update via XMODEM protocol

Requirements

A board with two UART peripherals
One UART connected to the host console (typically USB CDC-ACM or ST-LINK)
Second UART connected to a cellular modem
Device tree configuration for both UARTs

Wiring

The sample requires two UART connections to be defined in the device tree:

zephyr,console - Console UART for host communication
zephyr,modem-uart - Modem UART for cellular modem communication

Building and Running

Build and flash the sample as follows:

west build -b <your_board> samples/drivers/modem/at_client
west flash

After flashing, open a serial terminal to the console UART. Any AT commands typed will be forwarded to the modem, and responses will be displayed.

Sample Output

*** Booting Zephyr OS build v3.x.x ***
[00:00:00.100,000] <inf> at_client: Console UART pipe registered
[00:00:00.150,000] <inf> at_client: Modem pipe initialized and opened
[00:00:00.151,000] <inf> at_client: Console <-> Modem communication established
[00:00:00.151,000] <inf> at_client: Ready to forward AT commands


AT
OK

AT+CGMI
Sierra Wireless
OK

Usage Example

Once running, you can send AT commands directly from your terminal:

AT+CGSN                  # Query modem IMEI
AT+CSQ                   # Check signal quality
AT+COPS?                 # Query operator
AT+CGDCONT=1,"IP","apn"  # Configure APN

Firmware Update

This sample supports modem firmware updates using the XMODEM protocol. Use the companion Python script hl78xx_firmware_update.py to perform firmware updates through the AT client bridge.

See scripts/hl78xx_firmware_update.py for details.