AVR串口中断模式程序实例

/* Code adapted from Atmel AVRApplICation Note AVR306
* Interrupt mode driver for UART.
*/
#include
#include
#include "uart.h"

/* IMPORTANT: these vector numbers are for 8515! If you use other devices

* you must change them to the different set of numbers.
*
* UART_RX_interrupt set to UART, Rx Complete
* UART_TX_interrupt set to UART Data Register Empty
*/

#pragma interrupt_handler UART_RX_interrupt:10 UART_TX_interrupt:11

/* UART Buffer Defines */
#define UART_RX_BUFFER_SIZE 128 /* 1,2,4,8,16,32,64,128 or 256 bytes */
#define UART_RX_BUFFER_MASK ( UART_RX_BUFFER_SIZE - 1 )
#define UART_TX_BUFFER_SIZE 128 /* 1,2,4,8,16,32,64,128 or 256 bytes */
#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

/* Static Variables */
static unsigned char UART_RxBuf[UART_RX_BUFFER_SIZE];
static volatile unsigned char UART_RxHead;
static volatile unsigned char UART_RxTail;
static unsigned char UART_TxBuf[UART_TX_BUFFER_SIZE];
static volatile unsigned char UART_TxHead;
static volatile unsigned char UART_TxTail;

/* initialize UART */
void InitUART( unsigned char baudrate )
{
unsigned char x;
UBRR = baudrate; /* set the baud rate */
/* enable UART receiver and transmitter, and
receive interrupt */
UCR = ( (1<x = 0; /* flush receive buffer */
UART_RxTail = x;
UART_RxHead = x;
UART_TxTail = x;
UART_TxHead = x;
}

/* interrupt handlers */
void UART_RX_interrupt( void )
{
unsigned char data;
unsigned char tmphead;
data = UDR; /* read the received data */
/* calculate buffer index */
tmphead = ( UART_RxHead 1 ) & UART_RX_BUFFER_MASK;
UART_RxHead = tmphead; /* store new index */
if ( tmphead == UART_RxTail )
{
/* ERROR! Receive buffer overflow */
}
UART_RxBuf[tmphead] = data; /* store received data in buffer */
}

void UART_TX_interrupt( void )
{
unsigned char tmptail;

/* check if all data is transmitted */
if ( UART_TxHead != UART_TxTail )
{
/* calculate buffer index */
tmptail = ( UART_TxTail 1 ) & UART_TX_BUFFER_MASK;
UART_TxTail = tmptail; /* store new index */
UDR = UART_TxBuf[tmptail]; /* start transmition */
}
else
{
UCR &= ~(1<ISAble UDRE interrupt */
}
}

/* Read and write functions */
unsigned char ReceiveByte( void )
{
unsigned char tmptail;

while ( UART_RxHead == UART_RxTail ) /* wait for incomming data */
;
tmptail = ( UART_RxTail 1 ) & UART_RX_BUFFER_MASK;/* calculate buffer index */
UART_RxTail = tmptail; /* store new index */
return UART_RxBuf[tmptail]; /* return data */
}

void TransmitByte( unsigned char data )
{
unsigned char tmphead;
/* calculate buffer index */
tmphead = ( UART_TxHead 1 ) & UART_TX_BUFFER_MASK; 
/* wait for free sPACe in buffer */

while ( tmphead == UART_TxTail )
;
UART_TxBuf[tmphead] = data; /* store data in buffer */
UART_TxHead = tmphead; /* store new index */
UCR |= (1<}

unsigned char DataInReceiveBuffer( void )
{
return ( UART_RxHead != UART_RxTail ); 
/* return 0 (FALSE) if the receive buffer is empty */
}

#ifdef TEST
/* main - a simple test program*/
void main( void )
{
InitUART( 25 ); /* set the baudrate to 9600 bps using a 4MHz crystal */
_SEI(); /* enable interrupts => enable UART interrupts */
while ( 1 ) /* forever */
{
TransmitByte( ReceiveByte() ); /* echo the received character */
}
}
#endif