Do I have to write instructions in assembly? Im using Arduino IDE and im trying to sample a signal at 44.1khz. I come from a PIC Micro background where I would just use a TMR. Whats the play here in Arduino Land?

Hi guys,

I'm trying to implement something that will generate two triggers at regular intervals where the two triggers are separated by a configurable delay. The delay has to be configurable to sub microsecond resolution. Ideally, 500ns or less.

I chose the ESP32 because of its 240MHz clock, but it still seems to be having trouble.

I'm messing around with the following code:

#define cyclespermicro 240
#define microcycles(n) (n*cyclespermicro)

uint32_t startCounter, counter, cpu_cycles;
int cyclediff, totalcycles, corrected;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);

  startCounter = ESP.getCycleCount();
  totalcycles = startCounter + microcycles(2);
  //delayMicroseconds(1);

 while (ESP.getCycleCount() < totalcycles) {
        __asm__ __volatile__ ("nop");
 }
  
  counter = ESP.getCycleCount();
  cpu_cycles = counter - startCounter;
  corrected = cpu_cycles - 262;
  Serial.print("StartCounter: ");
  Serial.print(startCounter);
  Serial.print(" counter: ");
  Serial.print(counter);
  Serial.print(" cpu_cycles: ");
  Serial.print(cpu_cycles);
  Serial.print(" corrected: ");
  Serial.println(corrected);
}

void loop() {

}

The problem is that I get the same number of clock cycles for 1 us as I do for 2 us. I'm guessing this is because the while loop overhead is overwhelming the 1 us delay.

The problem is I need to have the amount of delay configurable and I don't know the best way to do this. Anyone have any ideas how to efficiently create configurable sub-microsecond delays?

EDIT: I am also noticing, when I get rid of the while loop entirely, and just straight up copy in NOP lines, it works as expected for like 3 NOPs, but once I hit 5 NOPS, the overhead jumps to like 500 cycles. What is going on here?