Ping-Pong Example (STM32F103CBT6 + Ra-20 / Ra-11) English Guide

Project Overview

This example demonstrates how to implement bidirectional LoRa Ping-Pong communication on an STM32F103CBT6 development board using the Semtech Radio Access Controller (RAC) to drive the LR2021 or Ra-11 RF chip.

1. Build Environment Setup (Detailed Steps)

1.1 Clone the Repository

git clone https://github.com/Ai-Thinker-Open/ra11-ra20.git Ra-20_Ra-11
cd Ra-20_Ra-11
git submodule update --init --recursive   # If the repository contains submodules

1.2 Install the Toolchain (Ubuntu / Debian / WSL2 Examples)

sudo apt update

# 1. ARM cross-compilation toolchain (10.x or 12.x recommended)
sudo apt install -y gcc-arm-none-eabi binutils-arm-none-eabi gdb-multiarch

# 2. Build system
sudo apt install -y cmake ninja-build

# 3. ST-Link flashing and debugging tools
sudo apt install -y stlink-tools

# 4. Python3 + pyserial (for debug.py serial monitoring and flashing helper scripts)
sudo apt install -y python3 python3-pip
pip3 install --user pyserial

# 5. Git (usually pre-installed)
sudo apt install -y git

1.3 Verify the Installation

Run the following commands to confirm that all tools have been installed successfully:

arm-none-eabi-gcc --version
cmake --version          # Requires ≥ 3.16
ninja --version
st-info --version
python3 -c "import serial; print('pyserial OK')"

1.4 Set Environment Variables (Optional)

If arm-none-eabi-gcc is not in the default PATH, please export the toolchain directory:

export ARM_GNU_BIN=/usr/bin
# or
export ARM_GNU_BIN=/opt/gcc-arm-none-eabi-10/bin

It is recommended to add the command above to ~/.bashrc or ~/.zshrc.

~/project/stm32_project/semtech_chip_driver/Ra-20_Ra-11/
├── examples/               # CMake entry point (includes README documentation)
├── smtc_rac_lib/
├── examples/smtc_hal_f1/   # F103-specific HAL
├── build/                  # Intermediate and final build files (can be deleted)
└── ...

2. Build Commands

rm -Rf build/ ; \
cmake -L -S examples \
      -B build \
      -DCMAKE_BUILD_TYPE=MinSizeRel \
      -DLEGACY_EVK_LR20XX=true \
      -DBOARD=STM32F103CB \
      -DRAC_RADIO=lr1121 \
      -G Ninja ; \
cmake --build build --target ping_pong

Common Variants

RF Chip Example Build Parameters Description
Ra-20 -DRAC_RADIO=lr2021 -DLEGACY_EVK_LR20XX=true Legacy EVK pin definition
Ra-11 -DRAC_RADIO=lr1121 Standard LR11xx pins
STM32F103CB -DBOARD=STM32F103CB ... Use STM32F103CB HAL

After a successful build, the following files will be generated in the build/ directory:

3. Hardware Wiring (STM32F103CBT6)

Common Pins (Ra-20 / LR1121 Compatible)

STM32F103CBT6 Pin RF Chip Pin Function Notes
PA4 NSS / CS SPI chip select —
PA5 SCK SPI clock —
PA6 MISO SPI MISO —
PA7 MOSI SPI MOSI —
PB14 NRST RF reset Active low
PB1 DIO1 / DIOX RF interrupt Rising-edge trigger
PA0 BUSY RF busy signal LR11xx / LR20xx
PA8 — LED_TX LED ON when transmitting
PB15 — LED_RX LED ON when receiving
PA9 UART_TX Debug UART 115200 8N1
PA10 UART_RX Debug UART —

Ra-20 (Legacy EVK Mode)

Ra-11

Power supply recommendation: The MCU and RF chip should share a 3.3V power supply. Place 100nF + 10µF decoupling capacitors close to each VDD pin.

4. Flash the Firmware

Using st-flash

st-flash --serial <ST-serial number> --reset write build/ping_pong.bin 0x08000000

Using STM32_Programmer_CLI

STM32_Programmer_CLI -c port=SWD sn=<ST-serial number> -w build/ping_pong.bin 0x08000000 -v -rst

5. Running and Verification

Dual-Board Configuration

Normal Runtime Log (Manager Side)

After successful operation, the following log should be seen continuously (counter increments):

INFO: smtc_rac_init
INFO: USP/RAC Version: 1.0.0 
...
INFO: starting ping-pong as manager
INFO: sending (value=0, delay=0ms)
INFO: usp/rac: transaction is starting
INFO: usp/rac: new event: transaction (transmission) has ended (success)
INFO: receiving...
INFO: usp/rac: transaction is starting
INFO: usp/rac: new event: transaction (reception) has ended (success)
INFO: payload is correct, continuing
INFO: sending (value=1, delay=250ms)
...

6. Common Troubleshooting