I am trying to generate an external interrupt. I have configured a pin as an InterruptIn pin and I am inputting a 50kHz square wave pulse into the pin and I am toggling a DigitalOut pin high and low when entering and leaving the ISR. However, I am seeing a 5us delay when entering and leaving the ISR on the scope and I cannot see where this delay is coming from. Can anyone shed any light on this situation?

Post your source so we can see it.

Here is a section of the source code in question:

DigitalOut ClockOut (p22);

void Timer1_IRQHandler(void)
{
    LPC_TIM1->IR = 1;
    LPC_TIM1->MR0 = 469;
     PhaseTick++;
    ClockOut = 1;
    if (PhaseTick >= 4)
    {
        PhaseTick = 0;
        LookCounterA++;
        LookCounterB++;
        LookCounterC++;    
                
        QDacSync = 0;
        QDacData = Lookup[LookCounterA] >> 4;
        QDacData |= 0x0000;
        QDac.write(QDacData);  
        QDacSync = 1;
       
        QDacSync = 0;
        QDacData = Lookup[LookCounterB] >> 4;
        QDacData |= 0x1000;
        QDac.write(QDacData);  
        QDacSync = 1;
       
        QDacSync = 0;
        QDacData = Lookup[LookCounterC] >> 4;
        QDacData |= 0x2000;
        QDac.write(QDacData);  
        QDacSync = 1;
       
        //update all outputs
        QDacSync = 0;
        QDacData = 0xA00F;
        QDac.write(QDacData);  
        QDacSync = 1;
       
    }
    ClockOut = 0;
}