C Code for Interfacing UART in AVR MCU

[Magneto]

uart.h Header File

#ifndef UART_H
#define UART_H
/************************************************************************
Software: AVR-GCC 3.3
Hardware: any AVR with built-in UART, tested on AT90S8515 at 4 Mhz
Usage: see Doxygen manual
************************************************************************/

/**
* @defgroup pfleury_uart UART Library
* @code #include <uart.h> @endcode
*
* @brief Interrupt UART library using the built-in UART with transmit and receive circular buffers.
*
* This library can be used to transmit and receive data through the built in UART.
*
* An interrupt is generated when the UART has finished transmitting or
* receiving a byte. The interrupt handling routines use circular buffers
* for buffering received and transmitted data.
*
* The UART_RX_BUFFER_SIZE and UART_TX_BUFFER_SIZE constants define
* the size of the circular buffers in bytes. Note that these constants must be a power of 2.
* You may need to adapt this constants to your target and your application by adding
* CDEFS += -DUART_RX_BUFFER_SIZE=nn -DUART_RX_BUFFER_SIZE=nn to your Makefile.
*
* @note Based on Atmel Application Note AVR306
* @author Peter Fleury [email protected] http://jump.to/fleury
*/

/**@{*/


#if (__GNUC__ * 100 + __GNUC_MINOR__) < 304
#error "This library requires AVR-GCC 3.4 or later, update to newer AVR-GCC compiler !"
#endif


/*
** constants and macros
*/

/** @brief UART Baudrate Expression
* @param xtalcpu system clock in Mhz
* @param baudrate baudrate in bps, e.g. 1200, 2400, 9600
*/
#define UART_BAUD_SELECT(baudRate,xtalCpu) ((xtalCpu)/((baudRate)*16l)-1)


/** Size of the circular receive buffer, must be power of 2 */
#ifndef UART_RX_BUFFER_SIZE
#define UART_RX_BUFFER_SIZE 32
#endif
/** Size of the circular transmit buffer, must be power of 2 */
#ifndef UART_TX_BUFFER_SIZE
#define UART_TX_BUFFER_SIZE 32
#endif



/*
** high byte error return code of uart_getc()
*/
#define UART_FRAME_ERROR 0x0800 /* Framing Error by UART */
#define UART_OVERRUN_ERROR 0x0400 /* Overrun condition by UART */
#define UART_BUFFER_OVERFLOW 0x0200 /* receive ringbuffer overflow */
#define UART_NO_DATA 0x0100 /* no receive data available */


/*
** function prototypes
*/

/**
@brief Initialize UART and set baudrate
@param baudrate Specify baudrate using macro UART_BAUD_SELECT()
@return none
*/
extern void uart_init(unsigned int baudrate);


/**
* @brief Get received byte from ringbuffer
*
* Returns in the lower byte the received character and in the
* higher byte the last receive error.
* UART_NO_DATA is returned when no data is available.
*
* @param void
* @return lower byte: received byte from ringbuffer
* @return higher byte: last receive status
* - \b 0 successfully received data from UART
* - \b UART_NO_DATA
* <br>no receive data available
* - \b UART_BUFFER_OVERFLOW
* <br>Receive ringbuffer overflow.
* We are not reading the receive buffer fast enough,
* one or more received character have been dropped
* - \b UART_OVERRUN_ERROR
* <br>Overrun condition by UART.
* A character already present in the UART UDR register was
* not read by the interrupt handler before the next character arrived,
* one or more received characters have been dropped.
* - \b UART_FRAME_ERROR
* <br>Framing Error by UART
*/
extern unsigned int uart_getc(void);


/**
* @brief Put byte to ringbuffer for transmitting via UART
* @param data byte to be transmitted
* @return none
*/
extern void uart_putc(unsigned char data);


/**
* @brief Put string to ringbuffer for transmitting via UART
*
* The string is buffered by the uart library in a circular buffer
* and one character at a time is transmitted to the UART using interrupts.
* Blocks if it can not write the whole string into the circular buffer.
*
* @param s string to be transmitted
* @return none
*/
extern void uart_puts(const char *s );


/**
* @brief Put string from program memory to ringbuffer for transmitting via UART.
*
* The string is buffered by the uart library in a circular buffer
* and one character at a time is transmitted to the UART using interrupts.
* Blocks if it can not write the whole string into the circular buffer.
*
* @param s program memory string to be transmitted
* @return none
* @see uart_puts_P
*/
extern void uart_puts_p(const char *s );

/**
* @brief Macro to automatically put a string constant into program memory
*/
#define uart_puts_P(__s) uart_puts_p(PSTR(__s))



/** @brief Initialize USART1 (only available on selected ATmegas) @see uart_init */
extern void uart1_init(unsigned int baudrate);
/** @brief Get received byte of USART1 from ringbuffer. (only available on selected ATmega) @see uart_getc */
extern unsigned int uart1_getc(void);
/** @brief Put byte to ringbuffer for transmitting via USART1 (only available on selected ATmega) @see uart_putc */
extern void uart1_putc(unsigned char data);
/** @brief Put string to ringbuffer for transmitting via USART1 (only available on selected ATmega) @see uart_puts */
extern void uart1_puts(const char *s );
/** @brief Put string from program memory to ringbuffer for transmitting via USART1 (only available on selected ATmega) @see uart_puts_p */
extern void uart1_puts_p(const char *s );
/** @brief Macro to automatically put a string constant into program memory */
#define uart1_puts_P(__s) uart1_puts_p(PSTR(__s))

/**@}*/


#endif // UART_H








uart.c File

/*************************************************************************
Software: AVR-GCC 3.3
Hardware: any AVR with built-in UART,
tested on AT90S8515 at 4 Mhz and ATmega at 1Mhz

DESCRIPTION:
An interrupt is generated when the UART has finished transmitting or
receiving a byte. The interrupt handling routines use circular buffers
for buffering received and transmitted data.

The UART_RX_BUFFER_SIZE and UART_TX_BUFFER_SIZE variables define
the buffer size in bytes. Note that these variables must be a
power of 2.

USAGE:
Refere to the header file uart.h for a description of the routines.
See also example test_uart.c.

NOTES:
Based on Atmel Application Note AVR306

*************************************************************************/
#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/signal.h>
#include <avr/pgmspace.h>
#include "uart.h"


/*
* constants and macros
*/

/* size of RX/TX buffers */
#define UART_RX_BUFFER_MASK ( UART_RX_BUFFER_SIZE - 1)
#define UART_TX_BUFFER_MASK ( UART_TX_BUFFER_SIZE - 1)

#if ( UART_RX_BUFFER_SIZE & UART_RX_BUFFER_MASK )
#error RX buffer size is not a power of 2
#endif
#if ( UART_TX_BUFFER_SIZE & UART_TX_BUFFER_MASK )
#error TX buffer size is not a power of 2
#endif

#if defined(__AVR_AT90S2313__) \
|| defined(__AVR_AT90S4414__) || defined(__AVR_AT90S4434__) \
|| defined(__AVR_AT90S8515__) || defined(__AVR_AT90S8535__) \
|| defined(__AVR_ATmega103__)
/* old AVR classic or ATmega103 with one UART */
#define AT90_UART
#define UART0_RECEIVE_INTERRUPT SIG_UART_RECV
#define UART0_TRANSMIT_INTERRUPT SIG_UART_DATA
#define UART0_STATUS USR
#define UART0_CONTROL UCR
#define UART0_DATA UDR
#define UART0_UDRIE UDRIE
#elif defined(__AVR_AT90S2333__) || defined(__AVR_AT90S4433__)
/* old AVR classic with one UART */
#define AT90_UART
#define UART0_RECEIVE_INTERRUPT SIG_UART_RECV
#define UART0_TRANSMIT_INTERRUPT SIG_UART_DATA
#define UART0_STATUS UCSRA
#define UART0_CONTROL UCSRB
#define UART0_DATA UDR
#define UART0_UDRIE UDRIE
#elif defined(__AVR_ATmega8__) || defined(__AVR_ATmega16__) || defined(__AVR_ATmega32__) \
|| defined(__AVR_ATmega8515__) || defined(__AVR_ATmega8535__) \
|| defined(__AVR_ATmega323__)
/* ATmega with one USART */
#define ATMEGA_USART
#define UART0_RECEIVE_INTERRUPT SIG_UART_RECV
#define UART0_TRANSMIT_INTERRUPT SIG_UART_DATA
#define UART0_STATUS UCSRA
#define UART0_CONTROL UCSRB
#define UART0_DATA UDR
#define UART0_UDRIE UDRIE
#elif defined(__AVR_ATmega163__)
/* ATmega163 with one UART */
#define ATMEGA_UART
#define UART0_RECEIVE_INTERRUPT SIG_UART_RECV
#define UART0_TRANSMIT_INTERRUPT SIG_UART_DATA
#define UART0_STATUS UCSRA
#define UART0_CONTROL UCSRB
#define UART0_DATA UDR
#define UART0_UDRIE UDRIE
#elif defined(__AVR_ATmega162__)
/* ATmega with two USART */
#define ATMEGA_USART0
#define ATMEGA_USART1
#define UART0_RECEIVE_INTERRUPT SIG_USART0_RECV
#define UART1_RECEIVE_INTERRUPT SIG_USART1_RECV
#define UART0_TRANSMIT_INTERRUPT SIG_USART0_DATA
#define UART1_TRANSMIT_INTERRUPT SIG_USART1_DATA
#define UART0_STATUS UCSR0A
#define UART0_CONTROL UCSR0B
#define UART0_DATA UDR0
#define UART0_UDRIE UDRIE0
#define UART1_STATUS UCSR1A
#define UART1_CONTROL UCSR1B
#define UART1_DATA UDR1
#define UART1_UDRIE UDRIE1
#elif defined(__AVR_ATmega64__) || defined(__AVR_ATmega128__)
/* ATmega with two USART */
#define ATMEGA_USART0
#define ATMEGA_USART1
#define UART0_RECEIVE_INTERRUPT SIG_UART0_RECV
#define UART1_RECEIVE_INTERRUPT SIG_UART1_RECV
#define UART0_TRANSMIT_INTERRUPT SIG_UART0_DATA
#define UART1_TRANSMIT_INTERRUPT SIG_UART1_DATA
#define UART0_STATUS UCSR0A
#define UART0_CONTROL UCSR0B
#define UART0_DATA UDR0
#define UART0_UDRIE UDRIE0
#define UART1_STATUS UCSR1A
#define UART1_CONTROL UCSR1B
#define UART1_DATA UDR1
#define UART1_UDRIE UDRIE1
#elif defined(__AVR_ATmega161__)
/* ATmega with UART */
#error "AVR ATmega161 currently not supported by this libaray !"
#elif defined(__AVR_ATmega169__)
/* ATmega with one USART */
#define ATMEGA_USART0
#define UART0_RECEIVE_INTERRUPT SIG_UART0_RECV
#define UART0_TRANSMIT_INTERRUPT SIG_UART0_DATA
#define UART0_STATUS UCSR0A
#define UART0_CONTROL UCSR0B
#define UART0_DATA UDR0
#define UART0_UDRIE UDRIE0
#endif


/*
* module global variables
*/
static volatile unsigned char UART_TxBuf[UART_TX_BUFFER_SIZE];
static volatile unsigned char UART_RxBuf[UART_RX_BUFFER_SIZE];
static volatile unsigned char UART_TxHead;
static volatile unsigned char UART_TxTail;
static volatile unsigned char UART_RxHead;
static volatile unsigned char UART_RxTail;
static volatile unsigned char UART_LastRxError;

#if defined( ATMEGA_USART1 )
static volatile unsigned char UART1_TxBuf[UART_TX_BUFFER_SIZE];
static volatile unsigned char UART1_RxBuf[UART_RX_BUFFER_SIZE];
static volatile unsigned char UART1_TxHead;
static volatile unsigned char UART1_TxTail;
static volatile unsigned char UART1_RxHead;
static volatile unsigned char UART1_RxTail;
static volatile unsigned char UART1_LastRxError;
#endif



SIGNAL(UART0_RECEIVE_INTERRUPT)
/*************************************************************************
Function: UART Receive Complete interrupt
Purpose: called when the UART has received a character
**************************************************************************/
{
unsigned char tmphead;
unsigned char data;
unsigned char usr;
unsigned char lastRxError;


/* read UART status register and UART data register */
usr = UART0_STATUS;
data = UART0_DATA;

/* */
#if defined( AT90_UART )
lastRxError = (usr & (_BV(FE)|_BV(DOR)) );
#elif defined( ATMEGA_USART )
lastRxError = (usr & (_BV(FE)|_BV(DOR)) );
#elif defined( ATMEGA_USART0 )
lastRxError = (usr & (_BV(FE0)|_BV(DOR0)) );
#elif defined ( ATMEGA_UART )
lastRxError = (usr & (_BV(FE)|_BV(DOR)) );
#endif

/* calculate buffer index */
tmphead = ( UART_RxHead + 1) & UART_RX_BUFFER_MASK;

if ( tmphead == UART_RxTail ) {
/* error: receive buffer overflow */
lastRxError = UART_BUFFER_OVERFLOW >> 8;
}else{
/* store new index */
UART_RxHead = tmphead;
/* store received data in buffer */
UART_RxBuf[tmphead] = data;
}
UART_LastRxError = lastRxError;
}


SIGNAL(UART0_TRANSMIT_INTERRUPT)
/*************************************************************************
Function: UART Data Register Empty interrupt
Purpose: called when the UART is ready to transmit the next byte
**************************************************************************/
{
unsigned char tmptail;


if ( UART_TxHead != UART_TxTail) {
/* calculate and store new buffer index */
tmptail = (UART_TxTail + 1) & UART_TX_BUFFER_MASK;
UART_TxTail = tmptail;
/* get one byte from buffer and write it to UART */
UART0_DATA = UART_TxBuf[tmptail]; /* start transmission */
}else{
/* tx buffer empty, disable UDRE interrupt */
UART0_CONTROL &= ~_BV(UART0_UDRIE);
}
}


/*************************************************************************
Function: uart_init()
Purpose: initialize UART and set baudrate
Input: baudrate using macro UART_BAUD_SELECT()
Returns: none
**************************************************************************/
void uart_init(unsigned int baudrate)
{
UART_TxHead = 0;
UART_TxTail = 0;
UART_RxHead = 0;
UART_RxTail = 0;

#if defined( AT90_UART )
/* set baud rate */
UBRR = (unsigned char)baudrate;

/* enable UART receiver and transmmitter and receive complete interrupt */
UART0_CONTROL = _BV(RXCIE)|_BV(RXEN)|_BV(TXEN);

#elif defined (ATMEGA_USART)
/* Set baud rate */
UBRRH = (unsigned char)(baudrate>>8);
UBRRL = (unsigned char) baudrate;

/* Enable USART receiver and transmitter and receive complete interrupt */
UART0_CONTROL = _BV(RXCIE)|(1<<RXEN)|(1<<TXEN);

/* Set frame format: asynchronous, 8data, no parity, 1stop bit */
#ifdef URSEL
UCSRC = (1<<URSEL)|(3<<UCSZ0);
#else
UCSRC = (3<<UCSZ0);
#endif

#elif defined (ATMEGA_USART0 )
/* Set baud rate */
UBRR0H = (unsigned char)(baudrate>>8);
UBRR0L = (unsigned char) baudrate;

/* Enable USART receiver and transmitter and receive complete interrupt */
UART0_CONTROL = _BV(RXCIE0)|(1<<RXEN0)|(1<<TXEN0);

/* Set frame format: asynchronous, 8data, no parity, 1stop bit */
#ifdef URSEL0
UCSR0C = (1<<URSEL0)|(3<<UCSZ00);
#else
UCSR0C = (3<<UCSZ00);
#endif

#elif defined ( ATMEGA_UART )
/* set baud rate */
UBRRHI = (unsigned char)(baudrate>>8);
UBRR = (unsigned char) baudrate;

/* Enable UART receiver and transmitter and receive complete interrupt */
UART0_CONTROL = _BV(RXCIE)|(1<<RXEN)|(1<<TXEN);

#endif

}/* uart_init */


/*************************************************************************
Function: uart_getc()
Purpose: return byte from ringbuffer
Returns: lower byte: received byte from ringbuffer
higher byte: last receive error
**************************************************************************/
unsigned int uart_getc(void)
{
unsigned char tmptail;
unsigned char data;


if ( UART_RxHead == UART_RxTail ) {
return UART_NO_DATA; /* no data available */
}

/* calculate /store buffer index */
tmptail = (UART_RxTail + 1) & UART_RX_BUFFER_MASK;
UART_RxTail = tmptail;

/* get data from receive buffer */
data = UART_RxBuf[tmptail];

return (UART_LastRxError << 8) + data;

}/* uart_getc */


/*************************************************************************
Function: uart_putc()
Purpose: write byte to ringbuffer for transmitting via UART
Input: byte to be transmitted
Returns: none
**************************************************************************/
void uart_putc(unsigned char data)
{
unsigned char tmphead;


tmphead = (UART_TxHead + 1) & UART_TX_BUFFER_MASK;

while ( tmphead == UART_TxTail ){
;/* wait for free space in buffer */
}

UART_TxBuf[tmphead] = data;
UART_TxHead = tmphead;

/* enable UDRE interrupt */
UART0_CONTROL |= _BV(UART0_UDRIE);

}/* uart_putc */


/*************************************************************************
Function: uart_puts()
Purpose: transmit string to UART
Input: string to be transmitted
Returns: none
**************************************************************************/
void uart_puts(const char *s )
{
while (*s)
uart_putc(*s++);

}/* uart_puts */


/*************************************************************************
Function: uart_puts_p()
Purpose: transmit string from program memory to UART
Input: program memory string to be transmitted
Returns: none
**************************************************************************/
void uart_puts_p(const char *progmem_s )
{
register char c;

while ( (c = pgm_read_byte(progmem_s++)) )
uart_putc(c);

}/* uart_puts_p */


/*
* these functions are only for ATmegas with two USART
*/
#if defined( ATMEGA_USART1 )

SIGNAL(UART1_RECEIVE_INTERRUPT)
/*************************************************************************
Function: UART1 Receive Complete interrupt
Purpose: called when the UART1 has received a character
**************************************************************************/
{
unsigned char tmphead;
unsigned char data;
unsigned char usr;
unsigned char lastRxError;


/* read UART status register and UART data register */
usr = UART1_STATUS;
data = UART1_DATA;

/* */
lastRxError = (usr & (_BV(FE1)|_BV(DOR1)) );

/* calculate buffer index */
tmphead = ( UART1_RxHead + 1) & UART_RX_BUFFER_MASK;

if ( tmphead == UART1_RxTail ) {
/* error: receive buffer overflow */
lastRxError = UART_BUFFER_OVERFLOW >> 8;
}else{
/* store new index */
UART1_RxHead = tmphead;
/* store received data in buffer */
UART1_RxBuf[tmphead] = data;
}
UART1_LastRxError = lastRxError;
}


SIGNAL(UART1_TRANSMIT_INTERRUPT)
/*************************************************************************
Function: UART1 Data Register Empty interrupt
Purpose: called when the UART1 is ready to transmit the next byte
**************************************************************************/
{
unsigned char tmptail;


if ( UART1_TxHead != UART1_TxTail) {
/* calculate and store new buffer index */
tmptail = (UART1_TxTail + 1) & UART_TX_BUFFER_MASK;
UART1_TxTail = tmptail;
/* get one byte from buffer and write it to UART */
UART1_DATA = UART1_TxBuf[tmptail]; /* start transmission */
}else{
/* tx buffer empty, disable UDRE interrupt */
UART1_CONTROL &= ~_BV(UART1_UDRIE);
}
}


/*************************************************************************
Function: uart1_init()
Purpose: initialize UART1 and set baudrate
Input: baudrate using macro UART_BAUD_SELECT()
Returns: none
**************************************************************************/
void uart1_init(unsigned int baudrate)
{
UART1_TxHead = 0;
UART1_TxTail = 0;
UART1_RxHead = 0;
UART1_RxTail = 0;


/* Set baud rate */
UBRR1H = (unsigned char)(baudrate>>8);
UBRR1L = (unsigned char) baudrate;

/* Enable USART receiver and transmitter and receive complete interrupt */
UART1_CONTROL = _BV(RXCIE1)|(1<<RXEN1)|(1<<TXEN1);

/* Set frame format: asynchronous, 8data, no parity, 1stop bit */
#ifdef URSEL1
UCSR1C = (1<<URSEL1)|(3<<UCSZ10);
#else
UCSR1C = (3<<UCSZ10);
#endif
}/* uart_init */


/*************************************************************************
Function: uart1_getc()
Purpose: return byte from ringbuffer
Returns: lower byte: received byte from ringbuffer
higher byte: last receive error
**************************************************************************/
unsigned int uart1_getc(void)
{
unsigned char tmptail;
unsigned char data;


if ( UART1_RxHead == UART1_RxTail ) {
return UART_NO_DATA; /* no data available */
}

/* calculate /store buffer index */
tmptail = (UART1_RxTail + 1) & UART_RX_BUFFER_MASK;
UART1_RxTail = tmptail;

/* get data from receive buffer */
data = UART1_RxBuf[tmptail];

return (UART1_LastRxError << 8) + data;

}/* uart1_getc */


/*************************************************************************
Function: uart1_putc()
Purpose: write byte to ringbuffer for transmitting via UART
Input: byte to be transmitted
Returns: none
**************************************************************************/
void uart1_putc(unsigned char data)
{
unsigned char tmphead;


tmphead = (UART1_TxHead + 1) & UART_TX_BUFFER_MASK;

while ( tmphead == UART1_TxTail ){
;/* wait for free space in buffer */
}

UART1_TxBuf[tmphead] = data;
UART1_TxHead = tmphead;

/* enable UDRE interrupt */
UART1_CONTROL |= _BV(UART1_UDRIE);

}/* uart1_putc */


/*************************************************************************
Function: uart1_puts()
Purpose: transmit string to UART1
Input: string to be transmitted
Returns: none
**************************************************************************/
void uart1_puts(const char *s )
{
while (*s)
uart1_putc(*s++);

}/* uart1_puts */


/*************************************************************************
Function: uart1_puts_p()
Purpose: transmit string from program memory to UART1
Input: program memory string to be transmitted
Returns: none
**************************************************************************/
void uart1_puts_p(const char *progmem_s )
{
register char c;

while ( (c = pgm_read_byte(progmem_s++)) )
uart1_putc(c);

}/* uart1_puts_p */


#endif