Arduino

Arduino Due

Arduino due uses 32bit ARM Cortex M3 processor, 84 MHz

Speed

digitalWrite(pin #, HIGH/LOW) is much slower compared to direct register programming. I compared behaviour of both functions separately. The first option was to look only on digitalWrite:

digitalWrite(pin#, HIGH);
delayMicroseconds(1);
digitalWrite(pin#, HIGH);
delayMicroseconds(1);

Secondly we looked on bare "C" code, and as it can be seen on a picture pulses follow 1 us without any delay, on the opposite the first signal is longer than it supposed to be around 3 us. Here is small program to compare speed of both functions.

#define LEDBIT (1<<21)
void setup() 
{
  pinMode(52, OUTPUT);
  pinMode(50, OUTPUT);
  PIOB->PIO_OWER |= LEDBIT;  // Enabled direct writing to ODSR
  Serial.begin(9600);  
}
void loop() 
{
     while(1)
 {  
   digitalWrite(50, HIGH);
   PIOB->PIO_ODSR = LEDBIT; // turn the LED on (HIGH is the voltage level)
   delayMicroseconds(1);              
  
   PIOB->PIO_ODSR = 0;    // turn the LED off by making the voltage LOW
   digitalWrite(50, LOW); // slower, although more scalable function
   delayMicroseconds(1);              
 }
}

C code (Arduino due)

void setup() {
 pinMode(36, OUTPUT);
PIOC->PIO_OWER |= (1<<4);
}

void loop(){     
while(1){
PIOC->PIO_SODR = (1<<4); //makes the pin HIGH
      PIOC->PIO_CODR = (1<<4); // makes the pin LOW
delayMicroseconds(1);
}
}
Gives 20-30ns.
Pin assignment:

Digital analog converter

I did DAC on 2 devices: Arduino nano +