Arduino Mega Encoder VISA synchronization in LABVIEW

[Alcamo]

Hello
I'm using arduino mega and i need to create some control system in Labview in real time.
I'm using a control and simulation loop and VISA to get a signal from arduino. My code in arduino:

volatile unsigned int counter = 0;  

void setup() {
  Serial.begin (9600);
 
  pinMode(2, INPUT);           
  pinMode(3, INPUT);           
  
  digitalWrite(2, HIGH);      
  digitalWrite(3, HIGH);       
 
 
  
  attachInterrupt(0, ai0, RISING);

  attachInterrupt(1, ai1, RISING);
}

void loop() {
  // Send the value of counter
  Serial.println (counter);
  delay(10);
}

void ai0() {
  // ai0 is activated if DigitalPin nr 2 is going from LOW to HIGH
  // Check pin 3 to determine the direction
  if(digitalRead(3)==LOW) {
    counter++;
  }else{
    counter--;
  }
}

void ai1() {
  // ai0 is activated if DigitalPin nr 3 is going from LOW to HIGH
  // Check with pin 2 to determine the direction
  if(digitalRead(2)==LOW) {
    counter--;
  }else{
    counter++;
  }
}

Then i made a sketch. But i can't understand how to get visa read signal and control simulation synchronously. I'm trying to vary delay() in arduino code but the precision is not good.

[Alcamo]

How can I read VISA signal with program sinusoidal signal in one loop to use them together later??
if I try to read them together, then the SINE signal is displayed in real time, but the VISA signal gives me something wrong with big delays.
But separately in 2 loops all ok.