Second approach (CHIP-8)

#define CLOCK_FREQUENCY 60  // 60Hz
#define CLOCK_PERIOD 16.666f // Delay in milliseconds needed to achieve 60fps (1000/60=16.666)

void chip8_init(Chip8 *vm, int ips)
{
    // Initialize the VM ...

    // Instructions per frame. If ips=540 then ipf=9
    vm->IPF = ips / CLOCK_FREQUENCY;
}

void chip8_cycle(Chip8 *vm)
{
    // If ips=540 execute 9 instructions per cycle
    for (int i = 0; i < vm->IPF; i++) {
        fetch_decode_execute(vm);
    }

    chip8_decrease_timers(vm);
}

int main(int argc, char *argv[])
{
    if (argc != 3) {
        SDL_Log("Usage: %s <instr-per-sec> <rom-file>", argv[0]);
        return 1;
    }

    // Instructions per second executed by the VM (e.g. 540)
    int ips = SDL_atoi(argv[1]);

    // Read ROM file ...

    Chip8 vm;
    chip8_init(&vm, ips);
    chip8_load_rom(&vm, rom, rom_size);

    // Initialize graphics ...

    while (true) {
        Uint64 start = SDL_GetPerformanceCounter();

        // Handle input event ...

        chip8_cycle(&vm);

        // Update graphics ...

        Uint64 end = SDL_GetPerformanceCounter();
        double frequency = (double) SDL_GetPerformanceFrequency();
        double elapsed_time = ((end - start) * 1000) / frequency;

        if (elapsed_time < CLOCK_PERIOD)
            SDL_Delay((Uint32) (CLOCK_PERIOD - elapsed_time));
    }

    return 0;
}