#include "rcc.h"
#include "gpio.h"
#include "usart.h"

void usart2_init(void) {
  // Enable clock for GPIOA as USART2 is on PORT A pins
  RCC->AHB1ENR |= (1 << PORT('A'));

  // Configure PA2 and PA3 (USART2 pins) to use alternative functions
  uint16_t txPin = PIN('A', 2);
  gpio_set_mode(txPin, GPIO_MODE_AF);
  gpio_set_af(txPin, GPIO_AF_USART2_TX);

  uint16_t rxPin = PIN('A', 3);
  gpio_set_mode(rxPin, GPIO_MODE_AF);
  gpio_set_af(rxPin, GPIO_AF_USART2_RX);


  // Enable USART
  RCC->APB1ENR |= RCC_APB1ENR_USART2EN_ENABLE;

  // Clear control registers
  USART2->CR1 = 0;
  USART2->CR2 = 0;
  USART2->CR3 = 0;

  // Calculate Baud rate:
  // baud = f_clck / (8 * (2 - OVER8) * USARTDIV) =>
  // (8 * (2 - OVER8) * USARTDIV) = f_clock / baud =>
  // baud * (8 * (2 - OVER8) * USARTDIV) = f_clock =>
  // USARTDIV = (f_clock / (baud * (8 * (2 - OVER8)))

  // Target Baud rate = 115200, f_clock = 48MHz, OVER8 = 0
  // USARTDIV = 48E6 / (115200 * 8 * 2) = 26.0416666
  // mantissa = 26 = 0x1A
  // fraction = 0.041666 * 16 = 0.666656 ~= 1

  // baud = 48E6 / (8 * 2 * 26) = 115384.61538461539
  // error of 0.16% (115384.61538461539 / 115200 ) = 1.001602564102564
  //
  // skipping fractional part as error rate is good.

  USART2->BRR &= ~(USART_BRR_MANTISSA_MASK << USART_BRR_MANTISSA_BIT);
  USART2->BRR |= (0x1A << USART_BRR_MANTISSA_BIT);
  USART2->BRR &= ~(USART_BRR_FRACTION_MASK << USART_BRR_FRACTION_BIT);
  USART2->BRR |= (0x0 << USART_BRR_MANTISSA_BIT);

  // Enable transmitter and receiver
  USART2->CR1 |= USART_CR1_TE_ENABLE;
  USART2->CR1 |= USART_CR1_RE_ENABLE;
}

void usart2_start(void) {
  USART2->CR1 |= USART_CR1_UE_ENABLE;
}

void usart2_write_byte(uint8_t c) {
  USART2->DR = c;

  // Wait indefinitely for transmission to be ready for data
  while (!(USART2->SR & USART_SR_TC_COMPLETED));
}

void usart2_write(char *buf) {
  while (*buf) usart2_write_byte(*buf++);
}