SubGhz

Introduction

The SubGhz library gives low-level control of the sub-GHz radio module of the STM32WL series. The radio is a Semtech SX126x (SX1261 and SX1262 combined) integrated in the microcontroller and connected to a dedicated internal SPI bus.

The library offers an Arduino-style API to access the module: the user composes and sends the SPI commands. It does not provide a high-level interface to send or receive data. For LoRaWAN, see STM32LoRaWAN.

It defines a single class and a predefined instance named SubGhz.

SPI access

The dedicated SPI bus is available through SubGhz.SPI. It behaves like the Arduino SPI object. Pass SubGhz.spi_settings to beginTransaction() to run at the maximum supported speed (16 MHz, mode 0).

Internal signals

The Nss, Reset and Busy signals are internally connected to the RCC and PWR registers. No pinMode() is needed.

Method	Description
`void setNssActive(bool value)`	Activates NSS (drives it LOW) when `true`.
`bool isNssActive()`	Reads back the NSS value.
`void setResetActive(bool value)`	Puts the module in reset when `true`.
`bool isResetActive()`	Reads back the reset value.
`bool isBusy()`	Returns the radio busy signal.

The DIO signals cannot be read directly. They are only available through the radio interrupt.

Interrupt

The DIO signals are connected together in an OR configuration and drive a single level sensitive radio interrupt.

Method	Description
`void attachInterrupt(callback_function_t callback)`	Attaches and enables the handler, clearing any pending interrupt. Accepts any callable that `std::function<void(void)>` accepts.
`void detachInterrupt()`	Disables the interrupt and removes the handler.
`bool hasInterrupt()`	Returns `true` if a handler is attached, even when disabled.
`void enableInterrupt()`	Enables the interrupt again. If it triggered while disabled, the handler runs immediately.
`void disableInterrupt()`	Temporarily disables the interrupt.
`bool isInterruptPending()`	Returns `true` if the interrupt is pending.
`void clearPendingInterrupt()`	Clears the pending flag.

Warning

The handler must clear the interrupt flags in the radio or call disableInterrupt(). Otherwise the interrupt triggers again as soon as the handler returns.

Example

Initialize the radio and read a register with an SPI command:

#include <SubGhz.h>

void setup() {
  SubGhz.SPI.begin();
  SubGhz.setResetActive(false);

  // The radio starts in sleep mode with its busy signal active.
  SubGhz.SPI.beginTransaction(SubGhz.spi_settings);
  SubGhz.setNssActive(true);
  while (SubGhz.isBusy()) { /* wait */ }

  SubGhz.SPI.transfer(0x1D);                 // Read_Register() command
  SubGhz.SPI.transfer(0x07);                 // Register address MSB
  SubGhz.SPI.transfer(0x40);                 // Register address LSB
  uint8_t status = SubGhz.SPI.transfer(0x0); // Status
  uint8_t value = SubGhz.SPI.transfer(0x0);  // Register value

  SubGhz.setNssActive(false);
  SubGhz.SPI.endTransaction();
}

See the ReadRegister example of the library.