From 7c5fd66f92a8c5affe4f20c31fa045633f1e24d6 Mon Sep 17 00:00:00 2001
From: Neale Pickett <neale@woozle.org>
Date: Tue, 2 Jul 2013 19:54:39 -0600
Subject: [PATCH] Allow wider range of clocks

---
 Makefile |  7 ++++---
 avr.c    | 11 +++++------
 avr.h    |  4 ----
 main.c   | 34 ++++++++++++++++------------------
 4 files changed, 25 insertions(+), 31 deletions(-)

diff --git a/Makefile b/Makefile
index 0cacd4d..61330a7 100644
--- a/Makefile
+++ b/Makefile
@@ -12,9 +12,9 @@ LDFLAGS += -mmcu=$(MCU)
 AVDFLAGS += -p $(MCU)
 AVDFLAGS += -c usbtiny
 
-CLOCK_HZ = 16000000
-FUSES += -U lfuse:w:0xff:m
-FUSES += -U hfuse:w:0xd9:m
+CLOCK_HZ = 2000000
+FUSES += -U lfuse:w:0x7f:m
+FUSES += -U hfuse:w:0xdd:m
 FUSES += -U efuse:w:0xff:m
 
 
@@ -28,6 +28,7 @@ fuses:
 	avrdude $(AVDFLAGS) $(FUSES)
 	
 main: main.o avr.o
+avr.o: CFLAGS += -DCLOCK_HZ=$(CLOCK_HZ)
 
 $(PROG).hex: $(PROG)
 	avr-objcopy -O ihex -R .eeprom -R .fuse -R .lock -R .signature $< $@
diff --git a/avr.c b/avr.c
index c6b1ba9..4fcb928 100644
--- a/avr.c
+++ b/avr.c
@@ -4,9 +4,8 @@
 #include <avr/interrupt.h>
 #include "avr.h"
 
-/* This only works out for a 16MHz or 8MHz clock */
-#define CLOCK_HZ 16000000
-#define TICKS_PER_SECOND (CLOCK_HZ / 256)
+/* Clock must be a multiple of 2MHz or there will be clock drift */
+#define TICKS_PER_SECOND (CLOCK_HZ / 64)
 #define TICKS_PER_JIFFY (TICKS_PER_SECOND / 10)
 
 #define cbi(byt, bit)   (byt &= ~_BV(bit))
@@ -34,9 +33,9 @@ init(void)
 	TCCR1B = 0;
 	TCNT1 = 0;
 	OCR1A = TICKS_PER_JIFFY - 1;
-	TCCR1B |= (1 << WGM12);
-	TCCR1B |= (1 << CS12);
-	TIMSK1 |= (1 << OCIE1A);
+	TCCR1B |= _BV(WGM12);
+	TCCR1B |= _BV(CS11) | _BV(CS10);
+	TIMSK1 |= _BV(OCIE1A);
 
 	sei();
 }
diff --git a/avr.h b/avr.h
index 12da855..4c2d5ce 100644
--- a/avr.h
+++ b/avr.h
@@ -5,10 +5,6 @@
 #include <avr/io.h>
 #include <avr/interrupt.h>
 
-// Make sure JIFFY_uS is going to be an integer and not a float!
-#define JIFFIES_PER_SECOND 100
-#define JIFFY_uS (1000000 / JIFFIES_PER_SECOND)
-
 #define bit(pin, bit, on) pin = (on ? (pin | bit) : (pin & ~bit))
 
 #define mode(on) bit(PORTA, _BV(0), on)
diff --git a/main.c b/main.c
index 197a88c..180c794 100644
--- a/main.c
+++ b/main.c
@@ -133,7 +133,7 @@ draw()
 	if ((state == TIMEOUT) && (jam_clock % 8 == 0)) {
 		// Blank it out
 		for (clk = 0; clk < 4; clk += 1) {
-			write(0);
+			write(setup_digits[1]);
 		}
 	} else {
 		clk = (abs(period_clock / 10) / 60) * 100;
@@ -254,24 +254,22 @@ loop()
 			PORTB ^= 0xff;
 		}
 
-		if (jiffies == 0) {
-			switch (state) {
-				case SETUP:
-					break;
-				case JAM:
-				case LINEUP:
-					if (period_clock) {
-						period_clock += 1;
-					}
-					// fall through
-				case TIMEOUT:
-					if (jam_clock) {
-						jam_clock += 1;
-					}
-			}
-
-			draw();
+		switch (state) {
+			case SETUP:
+				break;
+			case JAM:
+			case LINEUP:
+				if (period_clock) {
+					period_clock += 1;
+				}
+				// fall through
+			case TIMEOUT:
+				if (jam_clock) {
+					jam_clock += 1;
+				}
 		}
+
+		draw();
 	}
 }