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#include <avr/io.h>
#include <avr/interrupt.h>


#define USART0_BAUD_RATE(BAUD_RATE) ((float)(F_CPU * 64 / (16 * (float)BAUD_RATE)) + 0.5)

void uart_init(void) {
  // Set PA6 (the Tx pin) as output initialized to low.
  PORTA.OUTCLR = PIN6_bm;
  PORTA.DIRSET = PIN6_bm;

  // set baud_rate register
  USART0.BAUD = (uint16_t)USART0_BAUD_RATE(9600);

  // most interrupts and loopback disabled
  USART0.CTRLA = 0;

  // Only Tx enabled
  USART0.CTRLB = USART_TXEN_bm;

  // USART0.CTRLC defaults to 8/N/1 asynchronous
}

void _putc(const uint8_t v) {
  while (!(USART0.STATUS & USART_DREIF_bm)) {
  }
  USART0.TXDATAL = v;
}

void uart_write(uint16_t v) {
  // Synchronously write data
  uint16_t div = 10000;
  while (div > 0) {
    const uint8_t ch = '0' + v/div;
    v %= div;
    div /= 10;
    _putc(ch);
  }
  _putc('\r');
  _putc('\n');
  while (!(USART0.STATUS & USART_DREIF_bm)) {
  }
  _putc('\n');
}