103 lines
2.3 KiB
C
103 lines
2.3 KiB
C
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/* Based on Atmel Application Note AVR 306 */
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#include <avr/io.h>
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#include <avr/interrupt.h>
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#include <stdio.h>
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#ifndef BAUD
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#define BAUD 9600
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#endif
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#include <util/setbaud.h>
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#ifndef UART_RX_BUFFER_SIZE
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#define UART_RX_BUFFER_SIZE 32
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#endif
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#ifndef UART_TX_BUFFER_SIZE
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#define UART_TX_BUFFER_SIZE 256
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#endif
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struct tx_ring {
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int buffer[UART_TX_BUFFER_SIZE];
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int start;
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int end;
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};
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struct rx_ring {
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int buffer[UART_RX_BUFFER_SIZE];
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int start;
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int end;
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};
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static struct tx_ring tx_buffer;
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static struct rx_ring rx_buffer;
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/* http://www.cs.mun.ca/~rod/Winter2007/4723/notes/serial/serial.html */
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void uart_init(void) {
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tx_buffer.start = 0;
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tx_buffer.end = 0;
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rx_buffer.start = 0;
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rx_buffer.end = 0;
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UBRR0H = UBRRH_VALUE;
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UBRR0L = UBRRL_VALUE;
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UCSR0C = _BV(UCSZ01) | _BV(UCSZ00); /* 8-bit data */
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UCSR0B = _BV(RXEN0) | _BV(TXEN0); /* Enable RX and TX */
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sei();
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}
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int uart_putchar(char c, FILE *stream) {
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if (c == '\n') {
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uart_putchar('\r', stream);
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}
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int write_pointer = (tx_buffer.end + 1) % UART_TX_BUFFER_SIZE;
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if (write_pointer != tx_buffer.start){
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tx_buffer.buffer[tx_buffer.end] = c;
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tx_buffer.end = write_pointer;
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/* Data available. Enable the transmit interrupt for serial port 0. */
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UCSR0B |= _BV(UDRIE0);
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}
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return 0;
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}
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int uart_getchar(FILE *stream) {
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int read_pointer = (rx_buffer.start + 1) % UART_RX_BUFFER_SIZE;
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rx_buffer.start = read_pointer;
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return rx_buffer.buffer[read_pointer];
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}
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ISR(USART_RX_vect) {
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int write_pointer = (rx_buffer.end + 1) % UART_RX_BUFFER_SIZE;
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/* Add next byte to ringbuffer if it has space available. */
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if (write_pointer != rx_buffer.start){
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rx_buffer.buffer[rx_buffer.end] = UDR0;
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rx_buffer.end = write_pointer;
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}
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}
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ISR(USART_UDRE_vect){
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int read_pointer = (tx_buffer.start + 1) % UART_TX_BUFFER_SIZE;
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/* Transmit next byte if data available in ringbuffer. */
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if (read_pointer != tx_buffer.end) {
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UDR0 = tx_buffer.buffer[read_pointer];
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tx_buffer.start = read_pointer;
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} else {
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/* Nothing to send. Disable the transmit interrupt for serial port 0. */
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UCSR0B &= ~_BV(UDRIE0);
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}
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}
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