dthUSART – C library for AVR microcontrollers (beta) and example code

I decided to create a simple C library for USART and AVR microcontrollers for the purpose of studying the USART serial interface.

This library is likely to be often updated. Open source code on my github:
https://github.com/xdth/AVR_dthUSART

Below is an example application. It will echo back strings received via serial at 9600 bit rate (defined in dthUSART.h), using the internal oscillator at 1 Mhz.

dthUSART.h

/*
* dthUSART C library for AVR microcontrollers (beta)
* dthlabs.com - July 30, 2017
*/


/*
* Defines
*/
#ifndef F_CPU
#define F_CPU	1000000UL // CPU frequency is 1 Mhz
#endif

#ifndef BAUD
#define BAUD	0x0C // or 12, for 9600.00 bit rate at 1.000 MHz, U2Xn = 1 (asynchronous), error 0.2%
#endif

#ifndef USE_2X
#define USE_2X  1
#endif


/*
* Functions prototypes
*/
// USART_init
void USART_init(void);

// byte_transmit
void byte_transmit(unsigned char);

// byte_receive
unsigned char byte_receive(void);

// string_print
void string_print(const char myString[]);

// string_read
void string_read(char myString[], uint8_t maxLength);

dthUSART.c

/*
* dthUSART C library for AVR microcontrollers (beta)
* dthlabs.com - July 30, 2017
*/


/*
* Includes
*/
#include <avr/io.h>
#include "dthUSART.h"


/*
* USART_init
*/
void USART_init(void) {

  // Set baud rate
  UBRRH = (unsigned char)(BAUD>>8);
  UBRRL = (unsigned char)BAUD;

  // Set U2X
  #if USE_2X
    UCSRA |= (1 << U2X);
  #else
    UCSRA &= ~(1 << U2X);
  #endif
  
  // Enable receiver and transmitter
  UCSRB = (1 << RXEN) | (1 << TXEN);


  // Set frame format
  UCSRC = (1 << UCSZ1) | (1 << UCSZ0); // 8 data bits, 1 stop bit
}


/*
* byte_transmit
*/
void byte_transmit(unsigned char data) {
 // Wait for empty transmit buffer
 while ( !( UCSRA & (1 << UDRE)) );
 // Put data into buffer, sends the data
 UDR = data;
}


/*
* byte_receive
*/
unsigned char byte_receive(void) {
 // Wait for data to be received
 while ( !(UCSRA & (1 << RXC)) );
 // Get and return received data from buffer
 return UDR;
}


/*
* string_print
*/
void string_print(const char myString[]) {
  uint8_t i = 0;
  while (myString[i]) {
    byte_transmit(myString[i]);
    i++;
  }
}


/*
* string_read
*/
void string_read(char myString[], uint8_t maxLength) {
  char response;
  uint8_t i;
  i = 0;
  while (i < (maxLength - 1)) {       // avoid overun
    response = byte_receive();
    byte_transmit(response);
    if (response == '\r') {           // enter for ending
      break;
    }
    else {
      myString[i] = response;         // add char
      i++;
    }
  }
  myString[i] = 0;                    // end with terminal NULL char
}

main.c

/*
* UART echo demo
* Using dthUSART C library for AVR microcontrollers (beta)
* dthlabs.com - July 30, 2017
*/


/*
* CPU frequency
*/
#define F_CPU    1000000UL // CPU frequency is 1 Mhz


/*
* Includes
*/
#include <avr/io.h>
#include <string.h>          // strcmp()
#include <util/delay.h>
#include "dthUSART.h"        // dthUSART library


/*
* Main
*/
int main(void){

  // Initialize USART
  USART_init();
  _delay_ms(1000); // delay for a second

  // Send hello strings
  string_print("\r\n");
  string_print("+--------------------------------+ \r\n");
  string_print("|        dthlabs.com             +\r\n");
  string_print("+--------------------------------+ \r\n");
  string_print("\r\n");
  string_print("\r\n");
  string_print("\r\n");
  string_print("Type string to be echoed >\r\n");

  // declare buffer
  char data[100];

  // Loop forever
  for(;;) {
    // Read data
    string_read(data,100);

    // Echo data back
    string_print(data);
    string_print("\r\n");
   }

    // the program executed successfully
    return 0;
}