nRF9151 Rust Modem Project

Rust project for the nRF9151 using Embassy async runtime with the embassy-net-nrf91 modem driver.

Features

• Embassy async framework for embedded Rust
• Direct AT command interface to the modem
• UART logging at 115200 baud
• Network registration monitoring (CEREG)

Prerequisites

1. Install Rust target

rustup target add thumbv8m.main-none-eabihf

2. Install probe-rs for flashing/debugging

# Using cargo
cargo install probe-rs-tools

# Or using brew on macOS
brew install probe-rs

3. Flash modem firmware on the nRF9151

The nRF9151 requires Nordic's modem firmware to be flashed separately. Download it from: https://www.nordicsemi.com/Products/nRF9151/Download

Use nRF Connect for Desktop's Programmer app to flash the modem firmware.

Building

cargo build --release

Flashing and Running

cargo run --release

UART Logging

The application outputs logs via UART at 115200 baud:

• TX: P0.29
• RX: P0.28

Connect a serial terminal to view the output.

Project Structure

nrf9151-modem/
├── .cargo/
│   └── config.toml       # Target and runner configuration
├── src/
│   └── main.rs           # Application entry point with AT commands
├── Cargo.toml            # Dependencies (embassy-net-nrf91, embassy-nrf)
├── memory.x              # Memory layout (IPC + RAM regions)
└── README.md

Memory Layout

The project uses the following memory layout for modem IPC:

Region	Address	Size	Purpose
FLASH	0x00000000	1024K	Application code
IPC	0x20000000	64K	Modem shared memory (IPC)
RAM	0x20010000	192K	Application RAM

AT Commands

The example demonstrates basic AT command usage:

Command	Description
AT	Basic test command
AT+CFUN?	Query functional mode
AT+CFUN=1	Enable modem (full functionality)
AT+CEREG=2	Enable registration URCs
AT+CEREG?	Query registration status
AT+CGMR	Get modem firmware version
AT+CGSN	Get IMEI

CEREG Status Values

Value	Meaning
0	Not registered, not searching
1	Registered, home network
2	Not registered, searching
3	Registration denied
4	Unknown
5	Registered, roaming

Dependencies

This project uses Embassy git dependencies for compatible versions:

• embassy-executor - Async executor for Cortex-M
• embassy-nrf - nRF HAL with Embassy support (nrf9160-s feature)
• embassy-net-nrf91 - Modem driver for nRF91 series
• embassy-time - Async timers

Useful Resources

• Embassy framework
• embassy-net-nrf91 source
• Nordic nRF9151 documentation
• nRF AT Commands Reference

Troubleshooting

"No probe found"

• Ensure your DK is connected
• Check USB cable (some are charge-only)
• Try probe-rs list to see connected probes

AT commands hang / no response

• Ensure modem firmware is flashed on the device
• The modem firmware must be downloaded separately from Nordic
• Wait for "Modem ready!" message before sending commands

CEREG shows 0 (not registered)

• Check that a SIM card is inserted
• Verify antenna is connected
• Check signal strength in your location
• Some networks may take time to register (wait 30+ seconds)

Build errors with embassy crates

This project uses git dependencies from the Embassy repository. If you encounter version conflicts, ensure all embassy crates are from the same git revision.