Routines for asynchronous UART communication on the ATMega328P

uart.c

/*
 * uart.c
 *
 * Asynchronous UART example tested on ATMega328P (16 MHz)
 *
 * Toolchain: avr-gcc (4.3.3)
 * Editor: Eclipse Kepler (4)
 * Usage:
 * 		Perform all settings in uart.h and enable by calling initUART(void)
 * 		Compile:
 * 				make all
 *
 * Functions:
 * 		- First call initUART() to set up Baud rate and frame format
 *		- initUART() calls macros TX_START() and RX_START() automatically
 *		- To enable interrupts on reception, call RX_INTEN() macros
 *		- Call functions getByte() and putByte(char) for character I/O
 *		- Call functions writeString(char*) and readString() for string I/O
 *
 *  Created on: 21-Jan-2014
 *      Author: Shrikant Giridhar
 */

#include "uart.h"

// Debug Mode; comment out on Release
#define _DEBUG			0


/*! \brief Configures baud rate (refer datasheet) */
void initUART(void)
{
	// Not necessary; initialize anyway
	DDRD |= _BV(PD1);
	DDRD &= ~_BV(PD0);

	// Set baud rate; lower byte and top nibble
	UBRR0H = ((_UBRR) & 0xF00);
	UBRR0L = (uint8_t) ((_UBRR) & 0xFF);

	TX_START();
	RX_START();

	// Set frame format = 8-N-1
	UCSR0C = (_DATA << UCSZ00);

}

/*! \brief Returns a byte from the serial buffer
 * 	Use this function if the RX interrupt is not enabled.
 * 	Returns 0 on empty buffer
 */
uint8_t getByte(void)
{
	// Check to see if something was received
	while (!(UCSR0A & _BV(RXC0)));
	return (uint8_t) UDR0;
}


/*! \brief Transmits a byte
 * 	Use this function if the TX interrupt is not enabled.
 * 	Blocks the serial port while TX completes
 */
void putByte(unsigned char data)
{
	// Stay here until data buffer is empty
	while (!(UCSR0A & _BV(UDRE0)));
	UDR0 = (unsigned char) data;

}

/*! \brief Writes an ASCII string to the TX buffer */
void writeString(char *str)
{
	while (*str != '\0')
	{
		putByte(*str);
		++str;
	}
}

const char* readString(void)
{
	char rxstr[RX_BUFF];
	char* temp;
	temp = rxstr;

	while((*temp = getByte()) != '\n')
	{
		++temp;
	}

	return rxstr;
}

#if _DEBUG

	int main(void)
	{
		initUART();
		while(1)
		{
			writeString(readString());
			putByte('\r');
			putByte('\n');
		}
		return 0;
	}

#endif

uart.h

/*
 * uart.h
 *
 * UART example for ATMega328P clocked at 16 MHz
 *
 * TODO :-
 * 	- Implement string read function
 * 	- Optimize for size
 * 	- Add helper routines and compile to .a file
 *
 *  Created on: 22-Jan-2014
 *      Author: Shrikant Giridhar
 */

#ifndef UART_H_
#define UART_H_

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

/* Probably already defined somewhere else. Define here, if isn't. */
#ifndef FOSC
#define	FOSC			16000000UL
#endif

/* Settings */
#define _BAUD			9600					// Baud rate (9600 is default)
#define _DATA			0x03					// Number of data bits in frame = byte tranmission
#define _UBRR			(FOSC/16)/_BAUD - 1		// Used for UBRRL and UBRRH

#define RX_BUFF			10

/* Useful macros */
#define TX_START()		UCSR0B |= _BV(TXEN0)	// Enable TX
#define TX_STOP()		UCSR0B &= ~_BV(TXEN0)	// Disable TX
#define RX_START()		UCSR0B |= _BV(RXEN0)	// Enable RX
#define RX_STOP()		UCSR0B &= ~_BV(RXEN0)	// Disable RX
#define COMM_START()		TX_START(); RX_START()	// Enable communications

/* Interrupt macros; Remember to set the GIE bit in SREG before using (see datasheet) */
#define RX_INTEN()		UCSR0B |= _BV(RXCIE0)	// Enable interrupt on RX complete
#define RX_INTDIS()		UCSR0B &= ~_BV(RXCIE0)	// Disable RX interrupt
#define TX_INTEN()		UCSR0B |= _BV(TXCIE0)	// Enable interrupt on TX complete
#define TX_INTDIS()		UCSR0B &= ~_BV(TXCIE0)	// Disable TX interrupt

/* Prototypes */
void initUART(void);
uint8_t getByte(void);
void putByte(unsigned char data);
void writeString(char *str);
const char* readString(void);

#endif /* UART_H_ */