Fixing millis() overflow: changing millis() and the timer 0 overflow handler so that the millis count is updated in the interrupt, and so we don't need to do a conversion inside millis(). Updated to do list.

build/macosx/Arduino.xcodeproj/project.pbxproj

@@ -56,7 +56,7 @@
 			productName = App;
 			productReference = 33DD8FB6096AC8DA0013AF8F /* Arduino.app */;
 			productSettingsXML = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>
-<!DOCTYPE plist PUBLIC \"-//Apple Computer//DTD PLIST 1.0//EN\" \"http://www.apple.com/DTDs/PropertyList-1.0.dtd\">
+<!DOCTYPE plist PUBLIC \"-//Apple//DTD PLIST 1.0//EN\" \"http://www.apple.com/DTDs/PropertyList-1.0.dtd\">
 <plist version=\"1.0\">
 <dict>
 	<key>CFBundleDevelopmentRegion</key>
@@ -687,6 +687,7 @@
 		33FFFD3F0965B1E40016AC38 /* Project object */ = {
 			isa = PBXProject;
 			buildConfigurationList = 33FFFD400965B1E40016AC38 /* Build configuration list for PBXProject "Arduino" */;
+			compatibilityVersion = "Xcode 2.4";
 			hasScannedForEncodings = 0;
 			mainGroup = 33FFFD3D0965B1E40016AC38;
 			productRefGroup = 33FFFD3D0965B1E40016AC38;

hardware/cores/arduino/wiring.c

@@ -24,26 +24,29 @@
 
 #include "wiring_private.h"
 
-// The number of times timer 0 has overflowed since the program started.
-// Must be volatile or gcc will optimize away some uses of it.
-volatile unsigned long timer0_overflow_count;
+volatile unsigned long timer0_clock_cycles = 0;
+volatile unsigned long timer0_millis = 0;
 
 SIGNAL(SIG_OVERFLOW0)
 {
-	timer0_overflow_count++;
+	// timer 0 prescale factor is 64 and the timer overflows at 256
+	timer0_clock_cycles += 64UL * 256UL;
+	while (timer0_clock_cycles > clockCyclesPerMicrosecond() * 1000UL) {
+		timer0_clock_cycles -= clockCyclesPerMicrosecond() * 1000UL;
+		timer0_millis++;
+	}
 }
 
 unsigned long millis()
 {
-	// timer 0 increments every 64 cycles, and overflows when it reaches
-	// 256.  we would calculate the total number of clock cycles, then
-	// divide by the number of clock cycles per millisecond, but this
-	// overflows too often.
-	//return timer0_overflow_count * 64UL * 256UL / (F_CPU / 1000UL);
+	unsigned long m;
+	uint8_t oldSREG = SREG;
 	
-	// instead find 1/128th the number of clock cycles and divide by
-	// 1/128th the number of clock cycles per millisecond
-	return timer0_overflow_count * 64UL * 2UL / (F_CPU / 128000UL);
+	cli();
+	m = timer0_millis;
+	SREG = oldSREG;
+	
+	return m;
 }
 
 void delay(unsigned long ms)
@@ -122,8 +125,6 @@ void init()
 	// work there
 	sei();
 	
-	// timer 0 is used for millis() and delay()
-	timer0_overflow_count = 0;
 	// on the ATmega168, timer 0 is also used for fast hardware pwm
 	// (using phase-correct PWM would mean that timer 0 overflowed half as often
 	// resulting in different millis() behavior on the ATmega8 and ATmega168)

todo.txt

@@ -1,14 +1,24 @@
 0012 arduino
 
+0012
+
+Add highByte(), lowByte(), and word(high, low) functions.
+Add bitRead() and bitWrite() functions (and bitSet() and bitClear()?)
+Add Encoder library.
+Add String library.
+Add Servo library.
+Add LiquidCrystal library.
+Fix millis() so it overflows on a nice variable-size boundary; see: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1205949448
+Move #include <WProgram.h> after other #include's?  (prevent it from interfering with standard libraries)
+[done] Factor out print statements into a common base class for Serial, LiquidCrystal, etc.
+
 AVR
 
-Fix millis() so it overflows on a nice variable-size boundary; see: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1205949448
 Consider moving millis() to timer 1, and configuring it so the interrupt is generated once a millisecond.
 Problems including WProgram.h twice?
 Add #defines for the analog input pins.
 Add parameter to shiftOut() for specifying a number of bits.
 Add parameter to Serial.print[ln](x, BIN) for specifying number of bits.
-Factor out print statements into a common base class for Serial, LiquidCrystal, etc.
 Add support for ATmega1280 (e.g. timers, external interrupts, multiple serial ports).
 Add weak attribute to signal handlers: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1203798214
 Incorporate ladyada's new SoftwareSerial library.
@@ -20,13 +30,7 @@ Fix delayMicroseconds(0).
 Add sleep function(s).
 Add SPI library.
 Add pulseOut(), etc. functions from Wiring.
-Add String library.
-Add LiquidCrystal library.
-Add Servo library.
-Add Encoder library.
 Add Ping example.
-Add highByte(), lowByte(), and word(high, low) functions.
-Add bitRead() and bitWrite() functions (and bitSet() and bitClear()?)
 Include Arduino as AVR-ISP sketch in hardware/firmwares.
 Move type definitions into WConstants.h.
 Change core to use Arduino types (e.g. byte, boolean).