STM32 Arduino Stepper unipolar 5-wire motor driver

//#include <Stepper.h>

#define MOTOR_1 PA3
#define MOTOR_2 PA2
#define MOTOR_3 PA1
#define MOTOR_4 PA0
#define MOTOR_STEPS 400

//Stepper stepper(MOTOR_STEPS, MOTOR_1, MOTOR_2, MOTOR_3, MOTOR_4);
int delayTime = 10;
int phase = 0;
int mode = 0;
int stepCount = 0;
unsigned long starttime = 0;

void setup() {
  Serial.begin(9600);
  pinMode(MOTOR_1, OUTPUT);
  pinMode(MOTOR_2, OUTPUT);
  pinMode(MOTOR_3, OUTPUT);
  pinMode(MOTOR_4, OUTPUT);

  GPIOA->regs->BRR = 0b1111;
  //starttime = milis();
}

void loop() {
  /*stepper.step(1);
  Serial.println(stepCount);
  stepCount++;
  delay(500)*/
  if(mode == 0) {
    GPIOA->regs->BRR = 0b1111;
    GPIOA->regs->BSRR = 0b1 << phase;
    phase++;
    if(phase >= 4) phase = 0;
    delay(delayTime);
  } else if(mode == 1) {
    GPIOA->regs->BRR = 0b1111;
    GPIOA->regs->BSRR = 0b11 << phase*2;
    phase++;
    if(phase >= 2) phase = 0;
    delay(delayTime);
  } else if(mode == 2) {
    GPIOA->regs->BRR = 0b1111;
    GPIOA->regs->BSRR = 0b1 << 0;
    delay(delayTime);
    GPIOA->regs->BRR = 0b1 << 3;
    delay(delayTime);
    GPIOA->regs->BSRR = 0b1 << 1;
    delay(delayTime);
    GPIOA->regs->BRR = 0b1 << 0;
    delay(delayTime);
    GPIOA->regs->BSRR = 0b1 << 2;
    delay(delayTime);
    GPIOA->regs->BRR = 0b1 << 1;
    delay(delayTime);
    GPIOA->regs->BSRR = 0b1 << 3;
    delay(delayTime);
    GPIOA->regs->BRR = 0b1 << 2;
    delay(delayTime);
  }
  //delay( 1000 / (milis() - starttime) );


}