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Topic: Spurious interrupt response (Read 422 times) previous topic - next topic


I'm trying to simulate an X-Y display that is used to display ion images. The ions are rastered with an X raster time of about 90 microseconds and a Y time of about 12ms. A synchronising pulse is available at the start of each X and Y scan. Each ion produces a pulse of 300ns duration. The pulse rate can be up to 50k per second. I'm using a Due to determine the time from the start of each raster and the arrival of each ion. The data is transferred to a PC via UDP for real time display.

The system works well but there is a spurious signal about 7 microseconds in from the start of the X scan. This signal depends on the overall pulse rate and can be over 10% of the total signal at high rates. There is no sign of this signal on the data input line.

The following code is much simplified but exhibits the problem :

Code: [Select]
const int XInput = 33;
const int PulseInput = 25; 
  volatile boolean DataReady ;
  volatile unsigned long XTime;   
  volatile unsigned long PulseTime;
  volatile unsigned long XTimeDiff;
  int DataPoints = 6000;
  unsigned long Data[6000] ;   
  int i;
  int PulseCounter = 0;

void setup()

 pinMode(PulseInput, INPUT);
 attachInterrupt(XInput, XLine, RISING); 
 attachInterrupt(PulseInput, PulseDetected, RISING); 

void loop()

   if (DataReady == true)
      DataReady = false;       
      Data[PulseCounter] = XTimeDiff; 
      if(PulseCounter > DataPoints)
        for (i=0;i<DataPoints;i++)
       PulseCounter = 0;     

void XLine()

  XTime =  micros(); 
void PulseDetected()
  PulseTime =  micros();   
  XTimeDiff = PulseTime - XTime;
  DataReady =  true  ;   


I'm using version 1.6.7 of the IDE.
The problem manifests itself without the Ethernet card and also when I change input pins, detach interrupts during serial sending or limit data collection to one block of data.

I suspect the problem is associated with using micros() and interrupts together but I'm at a loss as to how to fix this.

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