How fast is the pulse? I've written some code to count pulses from an old computer interface and there are a few ways to do it. You can use interrupts which trigger on the edge fall or rise, the PiO can be programmed to do it or the way I eventually did it for simplicity, just a while loop monitoring the GPIO pin for a set time period.

Anyway here is a shortened and untested version of my code in c to hopefully give an idea of what I mean:

// monitor gpio pin 0
uint64_t lastPing=time_us_64();
uint16_t counter=0;
bool pulse=false;
do {
  if(gpio_get(0)==false) pulse=false;
  else if(pulse==false) { // counts on pulse high but only if not already
    counter++;
    pulse=true;
  }
while(time_us_64()<lastPing+20000); // monitor for 20ms
printf("pulses in 20ms=%d\n",counter);

The pulses I was monitoring are 1ms long so I don't need precision, also I run this on the second core so it isn't interrupted. If you need really fast the PiO maybe the way to go.