#include <stm32f0xx.h>

/*
#define LED_PIN 5
#define LED_ON() GPIOA->BSRRL |= (1 << 5)
#define LED_OFF() GPIOA->BSRRH |= (1 << 5)
*/



// NOTE: Can also write to the GPIOC->BSRR ( bit set reset register )
// Depending on position, it either sets the bit in the ODR or clears it.

#define LED_PIN 9
#define LED_ON() GPIOC->ODR |= (1 << LED_PIN )
#define LED_OFF() GPIOC->ODR &= ~(1 << LED_PIN )


#define PAUSE 1 * 1000 * 1000

void delay(unsigned long count) {
    unsigned long x;
    for (x=0; x < count; x++) {
        __asm("nop");
    }
}

/*
 * sets up pins and what not for UART2 use.
 */
void uart2_init() {

  // enable GPIO register clock which is on GPIOA
  RCC->AHBENR |= RCC_AHBENR_GPIOAEN;
  // enable UART2 clock
  RCC->APB1ENR |= RCC_APB1ENR_USART2EN;

  // configure TX pin (PA2) for output by setting MODER2 bit 0
  GPIOA->MODER |= GPIO_MODER_MODER2_0;
  GPIOA->MODER &= ~GPIO_MODER_MODER2_1;

  // ensure pullup/pulldown resistors disabled
  GPIOA->PUPDR &= ~(GPIO_PUPDR_PUPDR8|GPIO_PUPDR_PUPDR9);

  // set the output type to push pull by clearing the OTYPER bit ( on reset is set to push/pull )
  GPIOA->OTYPER &= ~GPIO_OTYPER_OT_2;

  // set the output speed of the pin to LOW SPEED by setting both bits low
  //GPIOA->OSPEEDR &= ~GPIO_OSPEEDR_OSPEEDR2;
  GPIOA->OSPEEDR |= GPIO_OSPEEDR_OSPEEDR2;

  // the USART2 registers should all be set to sane defaults on reset
  // disable the UART by clearing the UE bit
  USART2->CR1 &= ~USART_CR1_UE;

  // set baud rate
  GPIOA->BRR = (480000 / 96);

  // enable USART, transmit enable
  USART2->CR1 |= USART_CR1_UE | USART_CR1_TE;

  // clear Transmit Complete flag
  USART2->ICR |= USART_ICR_TCCF;

}

void uart2_tx(char c) {
  USART2->TDR = c;
  while ( ! (USART2->ISR & USART_ISR_TC) ) {
    __asm("nop");
  }
  USART2->ICR |= USART_ICR_TCCF;

}

int main() {
    /* Enbale GPIOA clock */
    //RCC->AHB1ENR |= RCC_AHB1ENR_GPIOAEN;
    // enable PC register clock
    RCC->AHBENR |= RCC_AHBENR_GPIOCEN;
    /* Configure GPIOA pin 5 as output */
    //GPIOC->MODER |= (1 << (LED_PIN << 1));
    GPIOC->MODER |= GPIO_MODER_MODER9_0;

    /* Configure GPIOA pin 5 in max speed */
    GPIOC->OSPEEDR |= (3 << (LED_PIN << 1));

    uart2_init();

    while (1) {
        LED_OFF();
        uart2_tx('0');
        uart2_tx('\n');
        delay(PAUSE);
        LED_ON();
        uart2_tx('1');
        uart2_tx('\n');
        delay(PAUSE);
    }

}