124 lines
2.3 KiB
C
124 lines
2.3 KiB
C
#define BAUD 38400
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#include <util/setbaud.h>
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#include <avr/io.h>
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#include <avr/interrupt.h>
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#if defined(__AVR_ATmega2560__)
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#define SERIAL_RX_ISR USART0_RX_vect
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#elif defined(__AVR_ATmega328__)
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#define SERIAL_RX_ISR USART_RX_vect
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#else
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#error Unknown target processor
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#endif
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void uart_putchar(char c);
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void on_error( const char* msg, uint8_t code )
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{
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uart_putchar('0' + code );
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uart_putchar(':');
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for(; *msg; ++msg )
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uart_putchar(*msg);
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}
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// Basic UART setup code from here:
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// https://appelsiini.net/2011/simple-usart-with-avr-libc/
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void uart_init(void)
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{
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UBRR0H = UBRRH_VALUE;
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UBRR0L = UBRRL_VALUE;
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#if USE_2X
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UCSR0A |= _BV(U2X0);
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#else
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UCSR0A &= ~(_BV(U2X0));
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#endif
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UCSR0C = _BV(UCSZ01) | _BV(UCSZ00); // 8-bit data
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UCSR0B = _BV(RXEN0) | _BV(TXEN0) | _BV(RXCIE0); // Enable RX and TX and RX intertupt enable
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}
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void uart_putchar(char c)
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{
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loop_until_bit_is_set(UCSR0A, UDRE0); // Wait until data register empty.
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UDR0 = c;
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}
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void uart_putchar_alt(char c)
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{
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UDR0 = c;
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loop_until_bit_is_set(UCSR0A, TXC0); // Wait until transmission ready.
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}
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char uart_getchar(void)
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{
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loop_until_bit_is_set(UCSR0A, RXC0); // Wait until data exists.
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return UDR0;
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}
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#define BUF_N (64) // size of receive buffer
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// Note that 'buf_i_idx' must be declared volatile or the
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// the compare in the main loop will not work.
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volatile int buf_i_idx = 0; // receive buffer input index
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int buf_o_idx = 0; // receive buffer output index
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// Receive buffer
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char buf[ BUF_N ];
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ISR(SERIAL_RX_ISR)
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{
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// receive the incoming byte
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buf[ buf_i_idx ] = uart_getchar();
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// advance the buffer input index
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buf_i_idx = (buf_i_idx + 1) % BUF_N;
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}
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int main (void)
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{
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char c;
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cli(); // mask all interupts
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uart_init(); // setup UART data format and baud rate
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sei(); // re-enable interrupts
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// set pin 5 of PORTB for output
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DDRB |= _BV(DDB5);
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uart_putchar('a');
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for(;;)
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{
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// if there are bytes waiting in the receive buffer
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if( buf_o_idx != buf_i_idx )
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{
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// get the waiting byte
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c = buf[buf_o_idx];
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// advance the buffer output index
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buf_o_idx = (buf_o_idx+1) % BUF_N;
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// transmit the buffer input index as an asii char.
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c += 1;
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PORTB ^= _BV(PORTB5);// toggle LED
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// transmit
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uart_putchar(c);
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}
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}
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}
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