#define RCC_SEGMENT_START 0x40021000
#define GPIOA_SEGMENT_START 0x50000000

volatile int *RCC_ioclock_enable = (volatile int*)(0x34 + RCC_SEGMENT_START);

volatile int *GPIO_MODE = (volatile int*)(0x00 + GPIOA_SEGMENT_START);
volatile int *GPIO_OT = (volatile int*)(0x04 + GPIOA_SEGMENT_START);
volatile int *GPIO_DATA_OUT = (volatile int*)(0x14 + GPIOA_SEGMENT_START);

void setup() {
  *RCC_ioclock_enable |= 0b1; // enable PORT A

  *GPIO_MODE &= ~(0b101010);
  *GPIO_MODE |= 0b010101; // set PA0, PA1, PA2 as OUTPUT

  *GPIO_OT &= ~(0b111); // PA0, PA1, PA2 in push-pull config
}

void loop() {
  // Red
  send_data(0b11011011);
  delay(500);

  // Green
  send_data(0b10110111);
  delay(500);

  // Purple
  send_data(0b01001011);
  delay(500);

}
void send_data(char data){
  *GPIO_DATA_OUT &= ~(0b10);
  spi_transfer(data);
  *GPIO_DATA_OUT |= 0b10;

}
void spi_transfer(char data){
  for(char n=0;n<8;n++){
    *GPIO_DATA_OUT &= ~(0b100);
    if(data & 0b1) *GPIO_DATA_OUT |= 0b1;
    else *GPIO_DATA_OUT &= ~(0b1);
    delay(1);
    *GPIO_DATA_OUT |= 0b100;
    data >>= 1;
  }
}