RFM69-STM32

Introduction

This is a protocol agnostic driver library for handling HopeRF's RFM69 433/868/915 MHz RF modules. This library is written for the STM32 family of controllers, but can easily be ported to other devices.

Support is also available for the +20 dBm high power modules called RFM69HW/RFM69HCW.

A CSMA/CA (carrier sense multiple access) algorithm can be enabled to avoid collisions. If you want to enable CSMA, you should initialize the random number generator before.

This library is based on polled operations although the RFM69 modules support interrupts, so you do not need additional pins except for the SPI data signals. This approach should be fast enough for nearly every application and makes the code and program flow easier to follow.

Usage

You have to provide your own functions for delay_ms and mstimer_get. Use the SysTick timer (for example) with a 1 ms resolution which is present on all ARM controllers. This is an example working on STM32 controllers:

volatile uint32_t uptime_ms = 0; ///< Uptime in ms

extern "C" void SysTick_Handler()
{
  uptime_ms++;
}

/** Wait for X milliseconds.
 *
 * @param ms Milliseconds
 */
void delay_ms(unsigned ms)
{
  uint32_t start = uptime_ms;
  while (uptime_ms - start < ms);
}

/** Initialize the millisecond timer. */
void mstimer_init(void)
{
  SysTick_CLKSourceConfig(SysTick_CLKSource_HCLK);
  SysTick_Config(SystemCoreClock / 1000);
}

/** Return the number of milliseconds since start.
 *
 * @return Milliseconds
 */
uint32_t mstimer_get(void)
{
  return uptime_ms;
}

If you want to port this library to other devices, you have to provide an SPI instance derived from the SPIBase (see spibase.hpp) class. As of now, classes for STM32L1x and STM32F0x devices are included in this library as examples.

Example

...

// initialize millisecond timer (based on the delay code above)
mstimer_init();
  
// setup SPI
SPI spiRF(SPI1);
spiRF.setPrescaler(SPI_BaudRatePrescaler_2);
spiRF.init();

// setup RFM69 and optional reset
RFM69 rfm69(&spiRF, GPIOA, GPIO_Pin_1, true); // false = RFM69W, true = RFM69HW
rfm69.setResetPin(GPIOA, GPIO_Pin_2);
rfm69.reset();

// init RF module and put it to sleep
rfm69.init();
rfm69.sleep();

// set output power
rfm69.setPowerDBm(10); // +10 dBm

// enable CSMA/CA algorithm
rfm69.setCSMA(true);

...

// send a packet and let RF module sleep
char testdata[] = {'H', 'e', 'l', 'l', 'o'};
rfm69.send(testdata, sizeof(testdata));
rfm69.sleep();

...

// check if a packet has been received
char rx[64];
int bytesReceived = rfm69.receive(rx, sizeof(rx));

if (bytesReceived > 0)
{
  printf("%d bytes received.", bytesReceived);
}

Power settings

The power settings of +20 dBm RFM69HW modules are a bit confusing. Look here for some explanations and experiments regarding power consumption, power output and RSSI values at the receiver.