codificação de escrita na serial nativa para AVR,

avr serial native coding.ino

#include <avr/io.h>

union floatBytes {
  double  f;
  unsigned long b;
};

void USART1_Init(unsigned int baud) { //Initialize USART hardware & settings for Serial Radio
  uint16_t baud_setting;
  // assign the baud_setting, a.k.a. ubrr (USART Baud Rate Register)
  if (((F_CPU == 16000000UL) && (baud == 57600)) || (baud_setting >4095))
  {
    UCSR0A = 0;
    baud_setting = (F_CPU / 8 / baud - 1) / 2;
  }else{
    UCSR0A = 1 << U2X0;
    baud_setting; = (F_CPU / 4 / baud - 1) / 2;
  }
  UBRR0H = baud_setting >> 8;
  UBRR0L = baud_setting;
  
  UCSR0B = (1 << TXEN0); //enable transmitter only

  //set the data bits, parity, and stop bits
  //UCSR0C |= 0x80; // select UCSRC register (shared with UBRRH)
  UCSR0C = (1 << UCSZ00) | (1 << UCSZ01); // Set frame format: 8data, 1 stop bit
}

/*
 * Transmit a byte of data over USART to the Serial Radio
 */
void USART1_Trans(unsigned char data) {
  while (!(UCSR0A & (1 << UDRE0))); //wait for transmition to complete
  UDR0 = data;
}

long long doubleUp(union floatBytes float32) {
  unsigned char sign = (float32.b >> 31) & 0x01;
  unsigned long fraction = float32.b & 0x007FFFFF;
  unsigned long exponent = (float32.b >> 23) & 0xFF;

  if ((float32.b & 0x7FFFFFFF) == 0) { //special case for +/- 0
    return (((long long)sign) << 63);
  }

  if (exponent == 0xFF) { //special case for +/- infinity, NAN
    return (((long long)sign) << 63) | 0x7FF0000000000000 | (((long long)fraction) << 29);
  }

  exponent = exponent + 1023 - 127;
  return (((long long)sign) << 63) | (((long long)exponent) << 52) | (((long long)fraction) << 29);
}


void setup() {
  USART1_Init(57600);

  double float32 = -7.51e-32;

  long long float64 = doubleUp((union floatBytes)float32);
  //long long float64 = 11111111111;

  USART1_Trans(float64 >> 56);
  USART1_Trans(float64 >> 48);
  USART1_Trans(float64 >> 40);
  USART1_Trans(float64 >> 32);
  USART1_Trans(float64 >> 24);
  USART1_Trans(float64 >> 16);
  USART1_Trans(float64 >> 8);
  USART1_Trans(float64);

  while (1);

  return 0;
}

void loop() {
  // put your main code here, to run repeatedly:

}