How fast is the LinkIt?

 The answer is 312 ns +/- 5 ns or about 3.2 MHz. I coded this simple toggle program:

#include <stdio.h>
#include <string.h>
#include "mraa/gpio.h"
#include "mraa/common.h"
#include <stdbool.h>

int main(int argc, char** argv)
{
  mraa_gpio_context gpio = NULL;
  const char* board_name = mraa_get_platform_name();
  int pinstate = 0;

  gpio = mraa_gpio_init(0);
  fprintf(stdout, "Welcome to libmraa\n  Version: %s\n  Running on %s (Ctrl+C to exit)\n", mraa_get_version(), board_name);

  if (gpio == NULL) {
    fprintf(stdout, "Could not initilaize gpio\n");
    return 1;
  }
  mraa_gpio_dir(gpio, MRAA_GPIO_OUT);

  pinstate = 0;
  while (true) {
    mraa_gpio_write(gpio, pinstate);
    pinstate = !pinstate;
  }

  return 0;
}

By comparison using the PINX command for an Arduino (Nano) was 375 ns +/-33ns:

void setup() {                
  // initialize the digital pin as an output.
  pinMode(2, OUTPUT);     
}

void loop() {
  while (true) {
    PIND=B00000100;
  }
}

Not using PINX, it is still 375 ns but the duty cycle is about 33%:

void setup() {                
  // initialize the digital pin as an output.
  pinMode(2, OUTPUT);     
}

void loop() {
  while (true) {
    PORTD|=B00000100;
    PORTD&=B11111011;
  }
}

If your wondering what straight Arduino code would look like (i.e. less the direct port manipulations):

void setup() {                
  // initialize the digital pin as an output.
  pinMode(2, OUTPUT);     
}

int state=0;
void loop() {
  while(true) {
    digitalWrite(2,state);
    state=!state;
  }
}

But now it takes 11.12 us! 

Now there is upside for the LinkIt with direct port manipulations as well but this is a project for another day!

AlanX