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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"
#if defined(__AVR_AT90USB162__) || defined(__AVR_ATmega16U2__) || defined(__AVR_ATmega32U2__) || defined(__AVR_ATmega16U4__) || defined(__AVR_ATmega32U4__) || defined(__AVR_AT90USB646__) || defined(__AVR_AT90USB647__) || defined(__AVR_AT90USB1286__) || defined(__AVR_AT90USB1287__)
# define UDRn UDR1
# define UBRRnL UBRR1L
# define UCSRnA UCSR1A
# define UCSRnB UCSR1B
# define UCSRnC UCSR1C
# define U2Xn U2X1
# define RXENn RXEN1
# define TXENn TXEN1
# define RXCIEn RXCIE1
# define UCSZn1 UCSZ11
# define UCSZn0 UCSZ10
# define UDRIEn UDRIE1
# define USARTn_UDRE_vect USART1_UDRE_vect
# define USARTn_RX_vect USART1_RX_vect
#elif defined(__AVR_ATmega32A__)
# define UDRn UDR
# define UBRRnL UBRRL
# define UCSRnA UCSRA
# define UCSRnB UCSRB
# define UCSRnC UCSRC
# define U2Xn U2X
# define RXENn RXEN
# define TXENn TXEN
# define RXCIEn RXCIE
# define UCSZn1 UCSZ1
# define UCSZn0 UCSZ0
# define UDRIEn UDRIE
# define USARTn_UDRE_vect USART_UDRE_vect
# define USARTn_RX_vect USART_RX_vect
#elif defined(__AVR_ATmega328__) || defined(__AVR_ATmega328P__)
# define UDRn UDR0
# define UBRRnL UBRR0L
# define UCSRnA UCSR0A
# define UCSRnB UCSR0B
# define UCSRnC UCSR0C
# define U2Xn U2X0
# define RXENn RXEN0
# define TXENn TXEN0
# define RXCIEn RXCIE0
# define UCSZn1 UCSZ01
# define UCSZn0 UCSZ00
# define UDRIEn UDRIE0
# define USARTn_UDRE_vect USART_UDRE_vect
# define USARTn_RX_vect USART_RX_vect
#endif
// These buffers may be any size from 2 to 256 bytes.
#define RX_BUFFER_SIZE 64
#define TX_BUFFER_SIZE 256
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();
UBRRnL = (F_CPU / 4 / baud - 1) / 2;
UCSRnA = (1 << U2Xn);
UCSRnB = (1 << RXENn) | (1 << TXENn) | (1 << RXCIEn);
UCSRnC = (1 << UCSZn1) | (1 << UCSZn0);
tx_buffer_head = tx_buffer_tail = 0;
rx_buffer_head = rx_buffer_tail = 0;
sei();
}
// Transmit a byte
void uart_write(uint8_t data) {
uint8_t i;
i = tx_buffer_head + 1;
if (i >= TX_BUFFER_SIZE) i = 0;
// return immediately to avoid deadlock when interrupt is disabled(called from ISR)
if (tx_buffer_tail == i && (SREG & (1 << SREG_I)) == 0) return;
while (tx_buffer_tail == i)
; // wait until space in buffer
// cli();
tx_buffer[i] = data;
tx_buffer_head = i;
UCSRnB = (1 << RXENn) | (1 << TXENn) | (1 << RXCIEn) | (1 << UDRIEn);
// sei();
}
// Receive a byte
uint8_t uart_read(void) {
uint8_t data, i;
while (rx_buffer_head == rx_buffer_tail)
; // wait for character
i = rx_buffer_tail + 1;
if (i >= RX_BUFFER_SIZE) i = 0;
data = rx_buffer[i];
rx_buffer_tail = i;
return data;
}
void uart_transmit(const uint8_t *data, uint16_t length) {
for (uint16_t i = 0; i < length; i++) {
uart_write(data[i]);
}
}
void uart_receive(uint8_t *data, uint16_t length) {
for (uint16_t i = 0; i < length; i++) {
data[i] = uart_read();
}
}
// Return whether the number of bytes waiting in the receive buffer is nonzero.
// Call this before uart_read() to check if it will need
// to wait for a byte to arrive.
bool uart_available(void) {
uint8_t head, tail;
head = rx_buffer_head;
tail = rx_buffer_tail;
if (head >= tail) return (head - tail) > 0;
return (RX_BUFFER_SIZE + head - tail) > 0;
}
// Transmit Interrupt
ISR(USARTn_UDRE_vect) {
uint8_t i;
if (tx_buffer_head == tx_buffer_tail) {
// buffer is empty, disable transmit interrupt
UCSRnB = (1 << RXENn) | (1 << TXENn) | (1 << RXCIEn);
} else {
i = tx_buffer_tail + 1;
if (i >= TX_BUFFER_SIZE) i = 0;
UDRn = tx_buffer[i];
tx_buffer_tail = i;
}
}
// Receive Interrupt
ISR(USARTn_RX_vect) {
uint8_t c, i;
c = UDRn;
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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