added rot13 uart example

examples/Makefile

@@ -11,7 +11,7 @@ EFUSE = 0x05
 
 ## === Source files ===
 # Main C file
-MAIN = uart_keyhandler.c
+MAIN = uart_echo_rot13.c
 # Extra C files in this folder
 LOCAL_SOURCE =
 

examples/uart_echo_rot13.c

@@ -0,0 +1,49 @@
+#include <avr/io.h>
+#include <avr/pgmspace.h>
+#include <avr/interrupt.h>
+
+#include "lib/meta.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);
+}