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avr_demo/arduino_lite/uart_async.c

103 lines
2.3 KiB
C

/* Based on Atmel Application Note AVR 306 */
#include <avr/io.h>
#include <avr/interrupt.h>
#include <stdio.h>
#ifndef BAUD
#define BAUD 9600
#endif
#include <util/setbaud.h>
#ifndef UART_RX_BUFFER_SIZE
#define UART_RX_BUFFER_SIZE 64
#endif
#ifndef UART_TX_BUFFER_SIZE
#define UART_TX_BUFFER_SIZE 64
#endif
struct tx_ring {
int buffer[UART_TX_BUFFER_SIZE];
int start;
int end;
};
struct rx_ring {
int buffer[UART_RX_BUFFER_SIZE];
int start;
int end;
};
static struct tx_ring tx_buffer;
static struct rx_ring rx_buffer;
/* http://www.cs.mun.ca/~rod/Winter2007/4723/notes/serial/serial.html */
void uart_init(void) {
tx_buffer.start = 0;
tx_buffer.end = 0;
rx_buffer.start = 0;
rx_buffer.end = 0;
UBRR0H = UBRRH_VALUE;
UBRR0L = UBRRL_VALUE;
UCSR0C = _BV(UCSZ01) | _BV(UCSZ00); /* 8-bit data */
UCSR0B = _BV(RXEN0) | _BV(TXEN0); /* Enable RX and TX */
sei();
}
int uart_putchar(char c, FILE *stream) {
if (c == '\n') {
uart_putchar('\r', stream);
}
int write_pointer = (tx_buffer.end + 1) % UART_TX_BUFFER_SIZE;
if (write_pointer != tx_buffer.start){
tx_buffer.buffer[tx_buffer.end] = c;
tx_buffer.end = write_pointer;
/* Data available. Enable the transmit interrupt for serial port 0. */
UCSR0B |= _BV(UDRIE0);
}
return 0;
}
int uart_getchar(FILE *stream) {
int read_pointer = (rx_buffer.start + 1) % UART_RX_BUFFER_SIZE;
rx_buffer.start = read_pointer;
return rx_buffer.buffer[read_pointer];
}
ISR(USART_RX_vect) {
int write_pointer = (rx_buffer.end + 1) % UART_RX_BUFFER_SIZE;
/* Add next byte to ringbuffer if it has space available. */
if (write_pointer != rx_buffer.start){
rx_buffer.buffer[rx_buffer.end] = UDR0;
rx_buffer.end = write_pointer;
}
}
ISR(USART_UDRE_vect){
int read_pointer = (tx_buffer.start + 1) % UART_TX_BUFFER_SIZE;
/* Transmit next byte if data available in ringbuffer. */
if (read_pointer != tx_buffer.end) {
UDR0 = tx_buffer.buffer[read_pointer];
tx_buffer.start = read_pointer;
} else {
/* Nothing to send. Disable the transmit interrupt for serial port 0. */
UCSR0B &= ~_BV(UDRIE0);
}
}