I want to produce quick square waveform for testing purposes. If I will use this code:

void setup()
{
 pinMode(2, OUTPUT);
}

void loop() 
{
 bitSet(PORTD, 2);
 bitClear(PORTD, 2);
} 

I will get expected pulses but I also will get these 6.25 us dips in waveform roughly every 1 ms.

I use latest Arduino 1.6.9 environment.

Whole loop cycle take 1 us which mean 16 instructions (62.5 ns per instruction). So I will get 125 ns high and rest of the time low signal.

Any idea what I'm doing wrong?

Same results if I use asm sbi and sci instead of macros bitSet/bitClear.

Thank you!

I want to produce quick square waveform for testing purposes. If I will use this code:

void setup()
{
 pinMode(2, OUTPUT);
}

void loop() 
{
 bitSet(PORTD, 2);
 bitClear(PORTD, 2);
} 

I will get expected pulses but I also will get these 6.25 us dips in waveform roughly every 1 ms.

I use latest Arduino 1.6.9 environment.

Whole loop cycle take 1 us which mean 16 instructions (62.5 ns per instruction). So I will get 125 ns high and rest of the time low signal.

Any idea what I'm doing wrong?

Same results if I use asm sbi and sci instead of macros bitSet/bitClear.

Thank you!

/*

So after yours advices and little bit further searching I came up with solution to produce clean square waveform. It make 2.66 Mhz and it's probably fastest what you can get:

void setup()
{
 pinMode(2, OUTPUT);
 noInterrupts();   
}

void loop() 
{
 while(true)
 {
 bitSet(PORTD, 2);
 bitClear(PORTD, 2);
 }
}