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#include <stdint.h>
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#include <avr/io.h>
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#include <avr/interrupt.h>
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#include "serial.h"
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static int rx_start = 0, rx_end = 0;
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static uint8_t rx_buffer[RX_BUFFER_SIZE];
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ISR(USART1_RX_vect) {
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  uint8_t data = UDR1;
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  int new_end = rx_end+1;
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  if (new_end == RX_BUFFER_SIZE) {
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    new_end = 0;
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  }
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  if (new_end == rx_start) {
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    // TODO warn of buffer overflow?
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  } else {
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    rx_buffer[rx_end] = data;
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    rx_end = new_end;
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  }
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}
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void serial_init() {
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  // baud = F_CPU / (div (UBRR + 1))
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  // where div = 16 if U2X = 0, or 8 otherwise
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  uint16_t ubrr = F_CPU / 8 / BAUD_RATE - 1;
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  UBRR1H = ubrr >> 8;
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  UBRR1L = ubrr;
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  // UMSEL = 0, asynchronous usart
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  // UPM = 0, parity check disabled
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  // USBS = 0, 1 stop bit
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  // UCSZ = 3, 8-bit
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  // U2X = 1, use 8 prescale instead of 16 for a more accurate baud rate
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  UCSR1A = _BV(U2X1);
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  UCSR1B = _BV(RXCIE1) | _BV(RXEN1) | _BV(TXEN1);
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  UCSR1C = _BV(UCSZ11) | _BV(UCSZ10);
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}
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int serial_read() {
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  int ret;
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  cli();
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  if (rx_start == rx_end) {
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    ret = -1;
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  } else {
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    ret = rx_buffer[rx_start];
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    rx_start++;
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    if (rx_start == RX_BUFFER_SIZE) {
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      rx_start = 0;
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    }
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  }
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  sei();
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  return ret;
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}
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void serial_flush() {
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  cli();
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  rx_start = 0;
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  rx_end = 0;
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  sei();
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}
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uint8_t serial_read_blocking() {
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  int c;
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  do {
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    c = serial_read();
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  } while (c < 0);
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  return c;
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}
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void serial_write(uint8_t* data, int length) {
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  int i;
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  for (i = 0; i < length; i++) {
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    while (!(UCSR1A & _BV(UDRE1)));
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    UDR1 = data[i];
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  }
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}