porklib: Simple library for programming Arduino in C
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avr-lib/examples/uart_echo_rot13/main.c

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#include <avr/io.h>
#include <avr/pgmspace.h>
#include <avr/interrupt.h>
#include "lib/uart.h"
//
// This example receives asynchronously characters over UART
// and prints them back encrypted with ROT13 cipher (the one used for
// hints in GeoCaching)
//
// Echo, but with ROT13.
ISR(USART_RX_vect)
{
char c = uart_rx();
if (c == 13) {
// print CRLF on enter
uart_tx(10);
uart_tx(13);
return;
}
// do the ROT13
if ((c >= 'a' && c <= 'm') || (c >= 'A' && c <= 'M')) {
c += 13;
} else
if ((c >= 'n' && c <= 'z') || (c >= 'N' && c <= 'Z')) {
c -= 13;
}
// Print the result
uart_tx(c);
}
void main()
{
uart_init(9600);
uart_isr_rx(1);
sei();
uart_puts_P(PSTR("ROT13 UART echo example\r\n"));
while(1);
}