From 7ce6f869a058b90e6e2cff2554296f6c3cbcfa63 Mon Sep 17 00:00:00 2001
From: Vineet K <git@vineetk.net>
Date: Fri, 19 Apr 2024 17:42:44 -0400
Subject: [PATCH] add rudimentary interrupt-less UART

add interrupt support at least for reading the commands that come over
UART
---
 notes.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

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));
 	}
 }