Kongduino kindly sent me a WisDuo RAK3272s few weeks ago, it is a a breakout board for RAK nice module (RAK3172) around the STM32WL5 system on chip from ST. Let’s see how to use STM32 CubeMX to generate the initialization files and the LoRaWAN stack, then setup Visual Studio code debugger.

1. STM32 CubeMX

Download STM32 CubeMX from ST website, install it as instructed.
Open it then create a new project thanks to ACCESS TO MCU SELECTOR. In the Part Number searchbox look for STM32WLE5CC then select STM32WLE5CCUx and Start Project. CubeMX will now create empty project with only the RF and oscillator pins initialized plus some core peripherals, we have to select the features we want:

1.1 Pinout & configuration tab

Analog -> ADC

Check Vrefint Channel, it will be used by the demo application.

Timers -> RTC

Check Activate Clock Source and Activate calendar. Add the following values in configuration section, tab User constants:

• RTC_PREDIV_A: ((1<<(15-RTC_N_PREDIV_S))-1)
• RTC_N_PREDIV_S: 10
• RTC_PREDIV_S: ((1<<RTC_N_PREDIV_S)-1)

In Parameters Settings tab:

• Bin mode: Free running binary mode
• Asynchronous predivider value: RTC_PREDIV_A

Connectivity -> SUBGHZ

Check Activated to use the LoRa IP.

Connectivity -> USART2

To send traces (printf) from the STM32 to the computer.

1. Select Mode to Asynchronous
2. In Configuration section, tab DMA Settings:
   1. Click on Add
   2. In DMA request select USART2 TX
   3. In Channel select DMA 1 channel 5
   4. In Direction select Memory to peripheral
   5. In Priority select Low
3. Tab GPIO Settings should already have:
   • PA2 as USART2_TX
   • PA3 as USART2_RX

Middleware -> LoRaWAN

Check enabled to add the LoRaWAN stack to the project then in the configuration section, tab LoRaWAN Middleware:

1. lorawan_conf: select your region
2. Tx Rfo Config: CONF RFO HP

In tab LoraWAN Application:

1. Application: End Node skeleton
2. LoRa App->Active region: Select your region

In tab Platform Settings:

Note: If you do not know which EUI/Key to use follow the chapter TTN OTAA Device Registration in RAK’s quickstart.

In tab LoRaWAN commissioning:

1. Check Static Device Eui
2. Fill LoRaWAN device eui, App/JoinEUI and Application key

System core -> NVIC

Check SUBGHZ Radio Interrupt.

Pin configuration

On the STM32 picture click on:

• Pin PB0: select VDDTCXO
• Pin PC14: select RCC_OSC32_IN
• Pin PC15: select RCC_OSC32_OUT

1.2 Clock Configuration tab

1. In RTC Clock Mux select LSE input
2. MSI RC can be pushed to 48000

1.3 Project Manager tab

Set Project name, then in Toolchain/IDE select Makefile.
The project is ready, click on GENERATE CODE in top right corner.

When generated you can open the folder in your favorite editor, I will use VS Code.

2. Configure the C code

Now the program skeleton is generated but it can not be compiled yet, otherwise the compiler with output warnings like:

#warning user to provide its board definitions pins

We have to provide some specifics about the radio pins. Download radio_board_if_c.patch and radio_board_if_h.patch, place them in the root directory of your project then:

patch -u LoRaWAN/Target/radio_board_if.c -i radio_board_if_c.patch
patch -u LoRaWAN/Target/radio_board_if.h -i radio_board_if_h.patch

3. Compile the binary

Download arm-none-eabi toolchain, add it to your path then it is as simple as make -j.

4. Flash the microcontroller

RAK official documentation is using a serial<>USB converter and the integrated STM32 serial bootloader to flash the firmware, but I prefer an ST-Link as I will also be able to debug the code.

4.1 ST-Link pinout and wiring

You can use an ST-Link or any Nucleo header as long as it is broke from the target board or the jumpers ST-LINK are removed. Then the connector SWD/CN4 must be wired to the RAK module, Nucleo’s serial<>USB converter can be used thanks to CN3:

4.2 Use ST-Link USB mass storage

You can flash the microcontroler by copy/pasting the .bin file in the ST Link folder.

4.3 OpenOCD

Required only if you want to use the debugger. As of december 2021 most OpenOCD releases does not yet include STM32WL support, it has to be compiled from the sources. The steps are easy for Linux:

1. git clone https://git.code.sf.net/p/openocd/code openocd-code
2. apt install make libtool pkg-config autoconf automake texinfo libusb-1.0-0 libusb-1.0-0-dev
3. ./bootstrap
4. ./configure --enable-stlink
5. make
6. make install

4.5 VS Code

Install the extension Cortex-Debug if you want to use the debugger, then edit the launch.json file, or create it if required, to have

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Cortex Debug",
            "cwd": "${workspaceRoot}",
            "executable": "./build/${workspaceFolderBasename}.elf",
            "request": "launch",
            "type": "cortex-debug",
            "servertype": "openocd",
            "configFiles": [
                "interface/stlink.cfg",
                "target/stm32wlx.cfg"
            ],
        }
    ]
}

5. LoRaWAN uplinks

Register your device in a network server like The Things Network, then you should see the JoinRequest/JoinAccept!

If you have any issue the project is available on Gitlab. The project also contains a populated SendTxData() function to actually send uplinks :)

6. Next steps

Now that we are connected to the network the next post should be about optimizing power consumption and enter in stop mode to only consume µAmps when not sending data.