Port changes from photoresistor branch

* Poll RTC by trigger, set via ISR
* Change blink state by trigger, set via ISR
* Set time compensation trigger in ISR
* Refresh clock by timer
* Re-calculate displayed time only ater rtcsync or when time adjusted by buttons
* Simplify draw algo

simpleclock.ino

@@ -20,20 +20,25 @@ const long adjust_interval = 200; // delay between consecutive number increments
 const long bounce_delay = 20;     // contact bounce compensation
 const int hrs_btn = A0;           // put hour adjusting button on A0 lane
 const int min_btn = A1;           // put minute adjusting button on A1 lane
-bool btn_pushed = false;          // is button pushed?
+volatile bool btn_pushed = false; // is button pushed?
-unsigned long currentPushTimer;
 unsigned long previousPushTimer = 0;
-uint8_t minutes;
-uint8_t hours;
 
 /* dot blinking stuff */
-unsigned long currentMillis;
+volatile bool dot = true;
-unsigned long previousMillis = 0;
-const long interval = 500;
-bool dot = true;
 
 /* time inaccuracy compensation flag */
-bool compflag = true;
+volatile bool compflag1 = true;
+volatile bool compflag2 = false;
+const uint8_t timeSkew = 8;          // assume that clock runs faster than should
+volatile bool timeSkewEven = false;  // comp. 1 additional second per 2 days
+
+/* time vars */
+volatile uint8_t mysecond;
+volatile uint8_t myminute;
+volatile uint8_t myhour;
+
+/* rtc sync flag */
+volatile bool rtcsync = true;
 
 void setup()
 {
@@ -69,22 +74,84 @@ void setup()
 	// setup control buttons
 	pinMode(hrs_btn, INPUT_PULLUP);
 	pinMode(min_btn, INPUT_PULLUP);
+	
+/* Timer stuff
+ * timer0 being used in millis() micros() delay() etc, it has 8 bit resolution
+ * timer2 being used in analogWrite() tone() notone(), it has 8 bit resolution
+ * timer1 being used in servo lib has 16 bit resolution
+ * We'll use timer1, since we have no mechanical parts and don't need servo lib
+ */
+	// initialize timer1
+	noInterrupts();           // disable all interrupts
+	TCCR1A = 0;
+	TCCR1B = 0;
+
+	TCNT1 = 34286;            // preload timer 65536-16MHz/256/2Hz
+	TCCR1B |= (1 << CS12);    // 256 prescaler 
+	TIMSK1 |= (1 << TOIE1);   // enable timer overflow interrupt
+	interrupts();             // enable all interrupts
+}
+
+ISR(TIMER1_OVF_vect)
+{
+/* Feed clock twice per second */
+	TCNT1 = 34286;            // preload timer
+	// do not read rtc if time beng adjusted by buttons
+	(btn_pushed) ? rtcsync : rtcsync = true;
+
+/* Also switch dot */
+	if (dot)
+		dot = false;
+	else
+		dot = true;
+
+/* time compensation magic */
+	if ((myhour == 21) and (myminute == 21) and (mysecond == 21)
+	    and (compflag2)) {
+		compflag1 = true;
+		(timeSkewEven) ? timeSkewEven = false : timeSkewEven;
+	}
+
+	if ((myhour == 21) and (myminute == 21) and (mysecond == 23)) {
+		compflag1 = false;
+		compflag2 = true;
+	}
 }
 
 void loop()
 {
-	currentMillis = millis();
+	unsigned long currentMillis = millis();
-	currentPushTimer = currentMillis;
-	char str[4];
-	float d;
 
-	clock.getTime();
+/*
+ * Let's implement time compenstion for individual rtc module time
+ * charachteristics. In in my case quartz resonator as inaccurate as
+ * about +8.5 seconds per 24 hours
+ */
+	if (compflag1 && compflag2) {
+		if (timeSkewEven) {
+			clock.fillByHMS(myhour, myminute, (mysecond - timeSkew - 1));
+		} else {
+			clock.fillByHMS(myhour, myminute, (mysecond - timeSkew));
+		}
+
+		clock.setTime();
+		compflag2 = false;
+	}
+
+	if (rtcsync) {
+		clock.getTime();
+		mysecond = clock.second;
+		myminute = clock.minute;
+		myhour = clock.hour;
+		updateTimeStr(myhour, myminute);
+		rtcsync = false;
+	}
 
 	// push button magic
 	if ((!btn_pushed) and
 	    ((digitalRead(hrs_btn) == LOW) or (digitalRead(min_btn) == LOW))) {
-		if (currentPushTimer - previousPushTimer >= initial_delay) {
+		if (currentMillis - previousPushTimer >= initial_delay) {
-			previousPushTimer = currentPushTimer;
+			previousPushTimer = currentMillis;
 			btn_pushed = true;
 		}
 	}
@@ -92,79 +159,47 @@ void loop()
 	if (btn_pushed and
 	    (digitalRead(hrs_btn) != LOW) and (digitalRead(min_btn) != LOW)) {
 		// compensate possible contact bounce with delay
-		if (currentPushTimer - previousPushTimer >= bounce_delay) {
+		if (currentMillis - previousPushTimer >= bounce_delay) {
 			btn_pushed = false;
 		}
 	}
 
 	if (btn_pushed) {
-		if (currentPushTimer - previousPushTimer >= adjust_interval) {
+		if (currentMillis - previousPushTimer >= adjust_interval) {
-			previousPushTimer = currentPushTimer;
+			previousPushTimer = currentMillis;
 
 			if (digitalRead(hrs_btn) == LOW) {
-				hours = clock.hour + 1;
+				myhour++;
-				(hours > 23) ? hours = 0 : hours;
+				(myhour > 23) ? myhour = 0 : myhour;
-				clock.fillByHMS(hours, clock.minute, 0);
+				clock.fillByHMS(myhour, myminute, 0);
 				clock.setTime();
 			}
 
 			if (digitalRead(min_btn) == LOW) {
-				minutes = clock.minute + 1;
+				myminute++;
-				(minutes > 59) ? minutes = 0 : minutes;
+				(myminute > 59) ? myminute = 0 : myminute;
-				clock.fillByHMS(clock.hour, minutes, 0);
+				clock.fillByHMS(myhour, myminute, 0);
 				clock.setTime();
 			}
 		}
-	}
 
-	if (currentMillis - previousMillis >= interval) {
+		updateTimeStr(myhour, myminute);
-		previousMillis = currentMillis;
-
-		if (dot)
-			dot = false;
-		else
-			dot = true;
-	}
-
-	/*
-	 * Let's implement time compenstion for individual rtc module time
-	 * charachteristics. In in my case quartz resonator as inaccurate as
-	 * +/- about 5-8 seconds per 24 hours, maybe its require more EMI
-	 * shielding?
-	 */
-
-	if ((clock.hour == 21) and (clock.minute == 21) and
-	    (clock.second == 21) and (compflag)) {
-		clock.fillByHMS(clock.hour, clock.minute, 14);
-		clock.setTime();
-		compflag = false;
-	}
-
-	if ((clock.hour == 21) and (clock.minute == 21) and
-	    (clock.second == 23) and (!compflag)) {
-		compflag = true;
-	}
-
-	// make blinking dot
-	if (clock.hour > 0) {
-		if (dot) {
-			Display.setNumber((clock.hour * 100 + clock.minute), 2);
-		} else {
-			Display.setNumber((clock.hour * 100 + clock.minute));
-		}
-	} else {
-		/* 0 o'clock is an exception, we don't want to see "00.00", we
-		   want see "0.00" or "0 00", so we have to use this "hack" */
-		if (dot) {
-			d = float(clock.minute) / 100;
-			Display.setNumber(d, 2);
-		} else {
-			sprintf(str, "%2d%02d", clock.hour, clock.minute);
-			Display.setChars(str);
-		}
 	}
 
 	Display.refreshDisplay();
 }
 
+void updateTimeStr(uint8_t h, uint8_t m)
+{
+	if (dot) {
+		char str[5];
+		sprintf(str, "%2d.%02d", h, m);
+		Display.setChars(str);
+	} else {
+		char str[4];
+		sprintf(str, "%2d%02d", h, m);
+		Display.setChars(str);
+	}
+}
+
 /* vim: set filetype=cpp: */