So it’s a follow-up to this answer. I simply created a terminal app with Xcode and basically pasted the code there but in a loop:

#include <stdint.h>
#include <stdio.h>
#include <string.h>

uint64_t getfreq(void) {
    uint64_t value=0;
    asm("isb; mrs %0, CNTVCT_EL0" : "=r"(value));
    return value;
}

int main() {
    do {
        printf("CNTVCT_EL0 = 0x%016llXn", getfreq());
    } while(1);
}

Issue I have is I get something like this as output:

CNTVCT_EL0 = 0x0000000104CB1910
CNTVCT_EL0 = 0x0000000000000001
CNTVCT_EL0 = 0x0000000000000001
CNTVCT_EL0 = 0x0000000000000001

Why is only the first time the value looks remotely valid (it’s the same if I don’t have a loop) – maybe I need to clear something with another asm instruction?

Xcode Version 15.4 (15F31d)
MacOS 14.5 (23F79)
Mac mini m1 (2020)