Add uart synchronous transmit

drivers/uart_tx.c

@@ -0,0 +1,13 @@
+#include "uart_tx.h"
+#include "uart.h"
+#include <avr/io.h>
+#include <avr/interrupt.h>
+
+void __attribute__ ((naked)) __attribute__ ((section (".init6"))) uart_tx_init() {
+  UCSR0B |= (1<<TXEN0);
+}
+
+void uart_putc(unsigned char c) {
+        while( ( UCSR0A & ( 1 << UDRE0 ) ) == 0 ) {}
+        UDR0 = c;
+}

drivers/uart_tx.h

@@ -0,0 +1 @@
+void uart_putc(unsigned char c);