thx M. Gibert :)

Interrupt/Interrupt.ino

@@ -1,11 +1,94 @@
+const int _portBaud = 9600; // baud rate of the serial port
+unsigned long samplingTimestamp = 0; 
+
+const unsigned int nbSamples = 10; //  number of samples to compute mean and std
+unsigned long sampleTimestamps[nbSamples]; // array containing the timestamps
+unsigned int sampleIndex = 0; // current sample index
+
+// predivisor: possible values 1, 8, 64, 256, 1024
+// Register TCCR#B
+// CS#0 -> 1
+// CS#1 -> 8
+// CS#0 CS#1 -> 64
+//CS#2 -> 256
+// CS#0 CS#2 -> 1024
+// register 0 and 2 are 8 bits -> max value 256
+// register 1 is 16 bits -> max value 65535
 
 
-void setup() {
-  // put your setup code here, to run once:
-  Serial.begin(9600);
-}
+void setup() 
+{
+  // initializes the serial port
+  Serial.begin(_portBaud);
 
-void loop() {
-  // put your main code here, to run repeatedly:
+  // stops interrupts
+  cli();
+
+  // sets timer1 interrupt at 1Hz
+  TCCR1A = 0;// set entire TCCR1A register to 0
+  TCCR1B = 0;// same for TCCR1B
+  TCNT1  = 0;// initialize counter value to 0
+  // sets compare match register for 1hz increments
+  OCR1A = 15624;// = (16*10^6) / (1*1024) - 1 (must be < 65536)
+  // turns on CTC mode
+  TCCR1B |= (1 << WGM12);
+  // set CS10 and CS12 bits for 1024 prescaler
+  TCCR1B |= (1 << CS12) | (1 << CS10);  
+  // enable timer compare interrupt
+  TIMSK1 |= (1 << OCIE1A);
+
+  //allow interrupts
+  sei();
 
 }
+
+
+ISR(TIMER1_COMPA_vect)
+{  
+	//change the 0 to 1 for timer1 and 2 for timer2
+	//interrupt commands here
+	
+	// initializes the timer
+	unsigned long startTime = micros();
+  
+	// estimates sampling duration
+	unsigned long samplingDuration = startTime - samplingTimestamp;
+	samplingTimestamp = startTime;
+  
+	//Serial.println(samplingDuration);
+	if (sampleIndex < nbSamples)
+	{
+		sampleTimestamps[sampleIndex] = samplingDuration;
+		sampleIndex++;
+	}		
+	
+	//reads data once on pin A0
+	analogRead(0);
+}
+
+
+void loop() 
+{
+	if (sampleIndex == nbSamples)
+	{
+		// average
+		double timestampAverage = 0;
+		for (int l_sample=0; l_sample < nbSamples; l_sample++)
+		{
+			timestampAverage += (double)sampleTimestamps[l_sample]/nbSamples;
+		}
+		Serial.print("average= ");
+		Serial.println(timestampAverage); // print the timestamp average
+		
+		// variance
+		double timestampVariance = 0;
+		for (int l_sample=0; l_sample < nbSamples; l_sample++)
+		{
+			timestampVariance += pow((double)(sampleTimestamps[l_sample]-timestampAverage), 2.0)/nbSamples;
+		}
+		Serial.print("variance= ");
+		Serial.println(timestampVariance); // print the timestamp average
+		
+		sampleIndex = 0;
+	}
+}