RTC6705_setFrequency

ESP32_RTC6705_setFrequency.ino

#include <Arduino.h>
#include <SPI.h>

#define SYNTHESIZERREGISTERA            0x00
#define SYNTHESIZERREGISTERB            0x01
#define SYNTHESIZERREGISTERC            0x02
#define RFVCODFCCONTROLREGISTER         0x03
#define VCOCONTROLREGISTER              0x04
#define VCOCONTROLREGISTERCONT          0x05
#define AUDIOMODULATORCONTROLREGISTER   0x06
#define PREDRIVERANDPACONTROLREGISTER   0x07
#define STATEREGISTER                   0x0F
#define READ_BIT                        0x00
#define WRITE_BIT                       0x01
#define PIN_SPI_SLAVE_SELECT            5

uint16_t freq = 5800;

static void rtc6705WriteRegister(uint32_t data)
{
  SPI.beginTransaction(SPISettings(10000000, LSBFIRST, SPI_MODE0));
  digitalWrite(PIN_SPI_SLAVE_SELECT, LOW);
  SPI.transferBits(data, NULL, 25);  
  digitalWrite(PIN_SPI_SLAVE_SELECT, HIGH);
  SPI.endTransaction();
}

// https://github.com/betaflight/betaflight/blob/c56690786d9e601bd41a8adcc87a0428d967710d/src/main/drivers/vtx_rtc6705_soft_spi.c#L143
void rtc6705WriteFrequency(uint32_t channel_freq)
{  
  uint32_t freq = 25 * channel_freq;
  uint32_t SYN_RF_N_REG = freq / 64;    
  uint32_t SYN_RF_A_REG = freq % 64;
  
  uint32_t data = SYNTHESIZERREGISTERB | (WRITE_BIT << 4) | (SYN_RF_A_REG << 5) | (SYN_RF_N_REG << 12);
  rtc6705WriteRegister(data);
}

void rtc6705ReadRegister(uint32_t reg)
{  
  uint32_t data = reg | (READ_BIT << 4);
  rtc6705WriteRegister(data);
}

void rtc6705ResetState()
{
  uint32_t data = STATEREGISTER | (WRITE_BIT << 4);  
  rtc6705WriteRegister(data);
  
}

void setup()
{
  Serial.begin(9600);
  
  pinMode(PIN_SPI_SLAVE_SELECT, OUTPUT);
  digitalWrite(PIN_SPI_SLAVE_SELECT, HIGH);

  SPI.begin();
  // rtc6705ResetState();
}

void loop()
{
  rtc6705WriteFrequency(freq);

  // rtc6705ReadRegister(SYNTHESIZERREGISTERB);

  Serial.println(freq);
  
  freq += 20;
  if (freq > 5880) {
    freq = 5740;
  }

  delay(3000);  
}