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/* UART Example for Teensy USB Development Board
* http://www.pjrc.com/teensy/
* Copyright (c) 2009 PJRC.COM, LLC
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
// Version 1.0: Initial Release
// Version 1.1: Add support for Teensy 2.0, minor optimizations
#include <avr/io.h>
#include <avr/interrupt.h>
#include "uart.h"
// These buffers may be any size from 2 to 256 bytes.
#define RX_BUFFER_SIZE 64
#define TX_BUFFER_SIZE 40
static volatile uint8_t tx_buffer[TX_BUFFER_SIZE];
static volatile uint8_t tx_buffer_head;
static volatile uint8_t tx_buffer_tail;
static volatile uint8_t rx_buffer[RX_BUFFER_SIZE];
static volatile uint8_t rx_buffer_head;
static volatile uint8_t rx_buffer_tail;
// Initialize the UART
void uart_init(uint32_t baud)
{
cli();
UBRR1 = (F_CPU / 4 / baud - 1) / 2;
UCSR1A = (1<<U2X1);
UCSR1B = (1<<RXEN1) | (1<<TXEN1) | (1<<RXCIE1);
//UCSR1C = (1<<UCSZ11) | (1<<UCSZ10);
tx_buffer_head = tx_buffer_tail = 0;
rx_buffer_head = rx_buffer_tail = 0;
UCSR1C = 0;
UCSR1C |= (1 << UMSEL10) | (1 << UCSZ10) | (1 << UCSZ11);
//use external clk by settting PD5 aka XCK1 to Input
DDRD |= 1<<5;
sei();
}
// Transmit a byte
void uart_putchar(uint8_t c)
{
uint8_t i;
i = tx_buffer_head + 1;
if (i >= TX_BUFFER_SIZE) i = 0;
while (tx_buffer_tail == i) ; // wait until space in buffer
//cli();
tx_buffer[i] = c;
tx_buffer_head = i;
UCSR1B = (1<<RXEN1) | (1<<TXEN1) | (1<<RXCIE1) | (1<<UDRIE1);
//sei();
}
// Receive a byte
uint8_t uart_getchar(void)
{
uint8_t c, i;
while (rx_buffer_head == rx_buffer_tail) ; // wait for character
i = rx_buffer_tail + 1;
if (i >= RX_BUFFER_SIZE) i = 0;
c = rx_buffer[i];
rx_buffer_tail = i;
return c;
}
// Return the number of bytes waiting in the receive buffer.
// Call this before uart_getchar() to check if it will need
// to wait for a byte to arrive.
uint8_t uart_available(void)
{
uint8_t head, tail;
head = rx_buffer_head;
tail = rx_buffer_tail;
if (head >= tail) return head - tail;
return RX_BUFFER_SIZE + head - tail;
}
// Transmit Interrupt
ISR(USART1_UDRE_vect)
{
uint8_t i;
if (tx_buffer_head == tx_buffer_tail) {
// buffer is empty, disable transmit interrupt
UCSR1B = (1<<RXEN1) | (1<<TXEN1) | (1<<RXCIE1);
} else {
i = tx_buffer_tail + 1;
if (i >= TX_BUFFER_SIZE) i = 0;
UDR1 = tx_buffer[i];
tx_buffer_tail = i;
}
}
// Receive Interrupt
ISR(USART1_RX_vect)
{
uint8_t c, i;
c = UDR1;
i = rx_buffer_head + 1;
if (i >= RX_BUFFER_SIZE) i = 0;
if (i != rx_buffer_tail) {
rx_buffer[i] = c;
rx_buffer_head = i;
}
}
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