From 8f258e4e02e1821692d39d87d4073e884bc2798a Mon Sep 17 00:00:00 2001
From: Vineet K <git@vineetk.net>
Date: Wed, 17 Apr 2024 10:07:39 -0400
Subject: [PATCH] use timer1 ctc mode instead of util/delay functions

---
 Makefile |  2 ++
 main.c   | 70 +++++++++++++++++++++++++++++++-------------------------
 2 files changed, 41 insertions(+), 31 deletions(-)

diff --git a/Makefile b/Makefile
index 9eba3af..17df02d 100644
--- a/Makefile
+++ b/Makefile
@@ -2,6 +2,8 @@ CC 	= avr-gcc
 CFLAGS	= -O2 -Wall -Wextra -Werror -mmcu=atmega328p
 OBJCOPY	= avr-objcopy
 
+PORT	?= /dev/ttyACM0
+
 all:
 	${CC} ${CFLAGS} main.c
 	${OBJCOPY} -j .text -j .data -O ihex a.out main.hex
diff --git a/main.c b/main.c
index 461a970..448d7f7 100644
--- a/main.c
+++ b/main.c
@@ -1,43 +1,42 @@
 /*
  *  EEL4746C - AVR Piano - Speaker Section
  *  speaker is connected to PD2 and ground
- *  buttons are connected to PB0-5, PC0-5, PD3-7
+, PD3-7
  *  the LCD Arduino UNO is connected to TX/RX (PD0/1)
  */
 
 #include <avr/io.h>
 #include <avr/interrupt.h>
 
-#define F_CPU	16000000UL
-#define __DELAY_BACKWARD_COMPATIBLE__ /* to use variables with _delay_u/ms */
-#include <util/delay.h>
+#define	T1_PRESCALAR	8
+#define FREQ(f)		(16e6 / f / T1_PRESCALAR / 2)
 
-#define P_RX	0
-#define P_TX	1
-#define P_SPKR	2
+#define P_RX		0
+#define P_TX		1
+#define P_SPKR		2
 
 unsigned short freqs[] = {
-	1 / 100 * 1e6 / 2,
-	1 / 200 * 1e6 / 2,
-	1 / 250 * 1e6 / 2,
-	1 / 300 * 1e6 / 2,
-	1 / 350 * 1e6 / 2,
-	1 / 400 * 1e6 / 2,
-	1 / 500 * 1e6 / 2,
-	1 / 600 * 1e6 / 2,
-	1 / 700 * 1e6 / 2,
-	1 / 750 * 1e6 / 2,
-	1 / 1000 * 1e6 / 2,
-	1 / 1250 * 1e6 / 2,
-	1 / 1500 * 1e6 / 2,
-	1 / 1750 * 1e6 / 2,
-	1 / 2000 * 1e6 / 2,
-	1 / 3000 * 1e6 / 2,
-	1 / 4000 * 1e6 / 2,
-	1 / 5000 * 1e6 / 2,
-	1 / 6000 * 1e6 / 2,
-	1 / 7000 * 1e6 / 2,
-	1 / 8000 * 1e6 / 2
+	FREQ(100),
+	FREQ(200),
+	FREQ(250),
+	FREQ(300),
+	FREQ(350),
+	FREQ(400),
+	FREQ(500),
+	FREQ(600),
+	FREQ(700),
+	FREQ(750),
+	FREQ(1000),
+	FREQ(1250),
+	FREQ(1500),
+	FREQ(1750),
+	FREQ(2000),
+	FREQ(3000),
+	FREQ(4000),
+	FREQ(5000),
+	FREQ(6000),
+	FREQ(7000),
+	FREQ(8000),
 };
 unsigned char note = 8;
 unsigned char buttonpressed = 1;
@@ -54,15 +53,24 @@ main(void)
 	PCMSK2 = ~(1 | (1 << 1) | (1 << 2));
 	PCICR = (1 << PCIE0) | (1 << PCIE1) | (1 << PCIE2);
 
+	TCCR1A = 0x00; // use timer1 CTC mode
+	TCCR1B = 1 << WGM12; // already prescaled by 8 in table
+
 	sei();
 
 	//for (;;);
 	for (unsigned char n = 0;; n = (n + 1) % 2) {
 		if (!buttonpressed && n == 0) continue;
-		_delay_us(freqs[note]);
-//		_delay_us(714.2857);
-//		_delay_us(70);
+
+		TCNT1 = 1;
+		OCR1A = freqs[note];
+		TCCR1B |= 1 << CS11;
+
+		while ((TIFR1 & (1 << OCF1A)) == 0);
+
 		PORTD ^= 1 << P_SPKR;
+		TIFR1 |= 1 << OCF1A;
+		TCCR1B &= ~(1 << CS11);
 	}
 }