add rudimentary interrupt-less UART

add interrupt support at least for reading the commands that come over
UART

1 files changed, 33 insertions, 0 deletions

diff --git a/notes.c b/notes.c
index 7c92b83..946ecd6 100644
--- a/notes.c
+++ b/notes.c
@@ -11,6 +11,9 @@
 #define T1_PRESCALAR    8
 #define FREQ(f)         (16e6 / f / T1_PRESCALAR / 2)
 
+#define HIGH(sn)        ((sn >> 8) & 0xff)
+#define LOW(sn)         (sn & 0xff)
+
 #define P_RX            0
 #define P_TX            1
 #define P_SPKR          2
@@ -74,6 +77,29 @@ ISR (PCINT2_vect)
         }
 }
 
+void
+usart_init(void)
+{
+        // 115200 bps, RX/TX enabled
+        UBRR0 = 8;
+        UCSR0B = (1 << RXEN0) | (1 << TXEN0);
+        UCSR0C = (1 << UCSZ01) | (1 << UCSZ00);
+}
+
+void
+usart_send(unsigned char c)
+{
+        while (!(UCSR0A & (1 << UDRE0)));
+        UDR0 = c;
+}
+
+unsigned char
+usart_read(void)
+{
+        while (!(UCSR0A & (1 << RXC0)));
+        return UDR0;
+}
+
 int
 main(void) 
 {
@@ -93,7 +119,10 @@ main(void)
 
         sei();
 
+        usart_init();
+
         // Sends Square wave to the Speaker When a Button is Pressed
+        unsigned short cycles = 0;
         for (unsigned char n = 0;; n = (n + 1) % 2) {
                 // check if any buttons are pressed, otherwise don't play a note
                 if (((PINB & PCMSK0) | (PINC & PCMSK1) | (PIND & PCMSK2)) == 0)
@@ -110,5 +139,9 @@ main(void)
                 PORTD ^= 1 << P_SPKR;
                 TIFR1 |= 1 << OCF1A;
                 TCCR1B &= ~(1 << CS11);
+                cycles = (cycles + 1) % 0xffff;
+
+                usart_send(HIGH(cycles));
+                usart_send(LOW(cycles));
         }
 }