ST B-L072Z-LRWAN1

Tags: chip:stm32 chip:stm32l0 chip:stm32l072

The B-L072Z-LRWAN1 is a LoRa and Sigfox discovery board built around the Murata CMWX1ZZABZ-091 module, which packs an STM32L072CZ microcontroller and a Semtech SX1276 sub-GHz transceiver into a single package. The board carries an SMA connector with a whip antenna, an on-board ST-LINK/V2-1 and Arduino Uno R3 compatible headers.

Board information

The board features:

• Murata CMWX1ZZABZ-091 module: STM32L072CZ (Cortex-M0+ up to 32 MHz, 192 KiB flash, 20 KiB RAM) plus an SX1276 transceiver

• Programmable RF power, up to +14 dBm on the RFO path and +20 dBm on PA_BOOST

• SMA and U.FL antenna connectors

• 32 MHz TCXO for the radio, powered from a GPIO

• On-board ST-LINK/V2-1 with mass storage programming and a virtual COM port

• Arduino Uno R3 headers plus the ST morpho extension headers

• Four LEDs and one user button

• USB 2.0 full speed device connector

• Powered from USB, from an external supply or from a battery

Board documentation: https://www.st.com/en/evaluation-tools/b-l072z-lrwan1.html

Clocking

NuttX runs the part from the internal 16 MHz RC oscillator through the PLL, which gives a 32 MHz system clock. No external crystal is needed for the microcontroller; the 32 MHz TCXO of the module belongs to the radio.

Serial console

USART2 is wired to the virtual COM port of the on-board ST-LINK and is the NuttX console in every configuration:

Signal	Pin
USART2_TX	PA2
USART2_RX	PA3

Settings are 115200 8N1. With the board plugged in, the port shows up as /dev/ttyACM0 on Linux.

LEDs

The board has four LEDs, all active high:

LED	Pin	Colour
LED1	PA5	Green, also Arduino D13
LED2	PB5	Green
LED3	PB6	Blue
LED4	PB7	Red

If CONFIG_ARCH_LEDS is selected, LED1 is driven by the OS to show the system state:

State	LED1
Idle stack created	ON
In an interrupt	Flashing
Signal handler, assertion	Flashing
The system has crashed	Blinking

Otherwise the four LEDs are available to the application through /dev/userleds when CONFIG_USERLED is selected.

Buttons

Button	Pin	Notes
B1 USER	PB2	Pulled up, active low, EXTI capable
B2 RESET	NRST	Resets the microcontroller

Radio

The SX1276 sits inside the module and is reached over SPI1. Besides the bus and the interrupt lines, three GPIOs drive the antenna switch and one powers the TCXO that clocks the radio:

Signal	Pin	Notes
SPI1_NSS	PA15	Chip select, driven as a GPIO
SPI1_SCK	PB3
SPI1_MISO	PA6
SPI1_MOSI	PA7
RESET	PC0	Active low
DIO0	PB4	Transmit and receive done, EXTI capable
DIO1	PB1
DIO2	PB0
DIO3	PC13
TCXO power	PA12	Active high, needs about 5 ms to settle
RX enable	PA1	Antenna switch towards RFI_HF
TX RFO enable	PC2	Antenna switch towards RFO_HF, up to +14 dBm
TX BOOST enable	PC1	Antenna switch towards PA_BOOST

The board support code powers the TCXO before registering the driver and picks the antenna switch position from the operating mode and the requested power: the RFO path is used up to 14 dBm and PA_BOOST above that. This board is wired for the high frequency band.

The driver itself, its configuration options and what has to match between two radios to make them hear each other are documented in SX127x LoRa radio.

Other peripherals

Interface	Pins
USART1	PA9 (TX), PA10 (RX), on the Arduino header
SPI2	PB12 (NSS), PB13 (SCK), PB14 (MISO), PB15 (MOSI)
I2C1	PB8 (SCL), PB9 (SDA)
ADC	PA0, PA4 and the other Arduino analogue pins

Flashing

The board can be programmed through its own ST-LINK or through an external debug probe on the SWD header.

With the ST-LINK, the simplest route is the mass storage device it exposes; copying the raw binary to it programs the flash:

$ cp nuttx.bin /media/<user>/DIS_L072Z/

openocd and st-flash work as well.

With a SEGGER J-Link on the SWD pins, use a command script:

$ cat > flash.jlink << EOF
h
loadbin nuttx.bin, 0x08000000
r
g
q
EOF
$ JLinkExe -device STM32L072CZ -if SWD -speed 4000 -autoconnect 1 \
           -nogui 1 -CommanderScript flash.jlink

The virtual COM port of a stand-alone J-Link is not connected to USART2 of this board, so the console still comes from the ST-LINK USB cable.

Configurations

Each configuration is selected with:

$ ./tools/configure.sh b-l072z-lrwan1:<name>
$ make

nsh

The basic NuttShell configuration over USART2, with the hello example built in. A good first check that the board boots.

adc

NuttShell plus the adc example, reading the ADC with software triggered conversions.

nxlines_oled

Runs the nxlines graphics example on an SSD1306 OLED display connected to I2C1 (PB8 and PB9), in one bit per pixel mode.

sx127x

NuttShell plus the sx127x example and the SX1276 driver registered at /dev/sx127x. The example defaults to FSK at 930 MHz; everything can be overridden from the command line:

nsh> sx127x -h
nsh> sx127x -m 0 -f 917200000 -t -p 14 -l 32   # transmit LoRa frames
nsh> sx127x -m 0 -f 917200000 -r               # receive them

lorawan_tx

The same interactive setup, but with the radio defaults already matching a public LoRaWAN network in the 915 MHz band: LoRa modulation, 917.2 MHz, 125 kHz bandwidth, spreading factor 7, CRC enabled and the 0x34 sync word. Useful to feed a gateway under test:

nsh> sx127x -m 0 -f 917200000 -t -p 14 -l 32 -i 5 -d 60

lorawan_beacon

The same radio settings without a shell: the example itself is the entry point and starts transmitting as soon as the board boots, which is what is needed when the board is driven from a debug probe and no console is wired. The command line of the example comes from CONFIG_INIT_ARGS, and the frequency, the payload size and the power from CONFIG_EXAMPLES_SX127X_RFFREQ, _TXDATA and _TXPOWER.

Talking to another radio

Two of these boards reach each other with the lorawan_tx configuration, one receiving and the other transmitting, and the same commands work against a LoRaWAN gateway. The recipes, and the settings that have to match on both sides, are in SX127x LoRa radio.