Factor uart code into separate driver code

drivers/uart.c

@@ -0,0 +1,10 @@
+#include "uart.h"
+#include <avr/io.h>
+
+#define BAUD_PRESCALE (((F_CPU/(BAUDRATE*8UL)))-1)
+
+void __attribute__ ((naked)) __attribute__ ((section (".init5"))) uart_init() {
+  UCSR0A = (1<<U2X0);
+  UCSR0C = (1<<UCSZ00) | (1<<UCSZ01); // 8N1
+  UBRR0 = BAUD_PRESCALE;
+}

drivers/uart_rx_async.c

@@ -0,0 +1,16 @@
+#include "uart_rx_async.h"
+#include "uart.h"
+#include <avr/io.h>
+#include <avr/interrupt.h>
+
+void __attribute__ ((naked)) __attribute__ ((section (".init6"))) uart_rx_async_init() {
+  UCSR0B = (1<<RXEN0) | (1<<RXCIE0);
+}
+
+void __attribute__ ((naked)) __attribute__ ((section (".init8"))) uart_rx_sei() {
+  sei();
+}
+
+ISR(USART_RX_vect) {
+  uart_process(UDR0);
+}

drivers/uart_rx_async.h

@@ -0,0 +1,3 @@
+#include <stdint.h>
+
+extern void uart_process(uint8_t c);