Makita speed control

#include <SPI.h>

SPISettings settingsPot(10000000, MSBFIRST, SPI_MODE0);

const byte speedControllerSSpin = 10; // Chip Select pin of the digital potentiometer
const byte spindleRelayPin = 7; // Pin to turn on/off the spindle with a relay

const int MIN_SPINDLE_RPM = 7930;
const int MAX_SPINDLE_RPM = 36330;
const float spindleK = (float)(MAX_SPINDLE_RPM - MIN_SPINDLE_RPM) / 256.0; // Slope of the linear function that converts RPM to 0-255 for the digital pot

int spindleSpeed = -1;
uint16_t spindleRPM = 0;

void setup()
{
  pinMode(speedControllerSSpin, OUTPUT);
  pinMode(spindleRelayPin, OUTPUT);
  digitalWrite(speedControllerSSpin, HIGH);
  digitalWrite(spindleRelayPin, LOW);
  SPI.begin(); // wake up the SPI bus.

  spindleSpeed = -1;
  sendSpindleSpeed();
}

void loop(){
    setSpindleRPM(10000); //Sets the spindle to 10k RPM
}

void setSpindleRPM(uint16_t rpm) {
  if (rpm < MIN_SPINDLE_RPM) {
    rpm = MIN_SPINDLE_RPM;
  }
  if ( rpm > MAX_SPINDLE_RPM ) {
    rpm = MAX_SPINDLE_RPM;
  }
  if (spindleRPM == rpm) {
    return;
  }
  spindleSpeed = floor((float)(rpm - MIN_SPINDLE_RPM) / spindleK);
  spindleRPM = rpm;
  sendSpindleSpeed();
}

void sendSpindleSpeed() {
  if (spindleSpeed >= 0) {
    noInterrupts();
    SPI.beginTransaction(settingsPot);
    digitalWrite(speedControllerSSpin, LOW);
    SPI.transfer(0); // send command byte
    SPI.transfer(spindleSpeed); // send value (0~255)
    digitalWrite(speedControllerSSpin, HIGH);
    digitalWrite(spindleRelayPin, HIGH);
    SPI.endTransaction;
    interrupts();
  }
  else {
    digitalWrite(spindleRelayPin, LOW);
  }
}