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85 lines
1.5 KiB
85 lines
1.5 KiB
#include <avr/io.h>
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#include <avr/interrupt.h>
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#include <stdint.h>
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#ifndef F_CPU
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#warning "F_CPU wasn't set in makefile, so we do it now with 10.0 MHz"
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#define F_CPU 10000000UL
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#endif
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// setting baud rate
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#define BAUD 9600UL
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// uart baud rate checks
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#define UBRR_VAL ((F_CPU+BAUD*8)/(BAUD*16)-1)
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#define BAUD_REAL (F_CPU/(16*(UBRR_VAL+1)))
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#define BAUD_ERROR ((BAUD_REAL*1000)/BAUD)
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#if ((BAUD_ERROR<990) || (BAUD_ERROR>1010))
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#warning baudrate error higher than 1%!
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#endif
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static void uart_init (void);
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static void uart_putc (unsigned char c);
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volatile uint8_t got_char;
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volatile unsigned char rx_char;
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int main (void)
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{
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// uart rx initialisation
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uart_init();
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// activate global interrupts
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sei();
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while(1)
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{
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if(got_char) {
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UCSR0B &= ~(1<<RXCIE0);
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uart_putc(rx_char);
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got_char = 0;
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UCSR0B |= (1<<RXCIE0);
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}
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}
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return 0;
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}
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// function to init uart
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static void uart_init (void) {
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// set baudrate registers (high byte first!)
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UBRR0H = UBRR_VAL >> 8;
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UBRR0L = UBRR_VAL & 0xFF;
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// tx enable
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UCSR0B |= (1<<TXEN0) | (1<<RXEN0) | (1<<RXCIE0);
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// frame format: async mode, no parity, 1 stop bit, 8 bit size
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UCSR0C |= (3<<UCSZ00);
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}
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// send a byte on uart
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static void uart_putc (unsigned char c) {
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while (!(UCSR0A & (1<<UDRE0))) {}
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UDR0 = c;
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}
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ISR(USART_RX_vect) {
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uint8_t rx_error = 0;
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//check for frame error
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if (UCSR0A & (1<<FE0)) {
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rx_error = 1;
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}
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// save rx buffer
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rx_char = UDR0;
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// signalise the new rx char if no frame error occured
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if (!rx_error) {
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got_char = 1;
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}
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}
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