[avr] Add test program for IO and basic usart

1 files changed, 37 insertions, 0 deletions

diff --git a/sw-avr/rom-loader/usart.c b/sw-avr/rom-loader/usart.c
new file mode 100644
index 0000000..5637d4f
--- /dev/null
+++ b/sw-avr/rom-loader/usart.c
@@ -0,0 +1,37 @@
+#include "usart.h"
+
+#include <avr/io.h>
+#include <util/setbaud.h>
+
+void usart_init(void)
+{
+    // automated by util/setbaud.h
+    UBRR0H = UBRRH_VALUE;
+    UBRR0L = UBRRL_VALUE;
+
+#if USE_2X
+    UCSR0A |= _BV(U2X0);
+#else
+    UCSR0A &= ~(_BV(U2X0));
+#endif
+
+    // 8 bit data
+    UCSR0C = _BV(UCSZ01) | _BV(UCSZ00);
+
+    // enable TX and RX pins
+    UCSR0B = _BV(RXEN0) | _BV(TXEN0);
+}
+
+void usart_send(uint8_t c)
+{
+    UDR0 = c;    
+    // wait until transmission ready
+    loop_until_bit_is_set(UCSR0A, TXC0); 
+}
+
+uint8_t usart_recv(void)
+{
+    // wait until data exists
+    loop_until_bit_is_set(UCSR0A, RXC0);
+    return UDR0;
+}