Hi igrr Thanks for your response. Just to make sure I understand, could you confirm that when you say "underlying XTAL clock source" this means the 40 MHz external XTAL? I understand the issue with the PLL. I believe this will add maximum jitter around the range of 1 x 40 MHz period, or 25 ns. If yo...

I am trying to do accurate timing using the ESP32 64 bit counter which use the 80 MHz APB clock. I need accuracies of 1 ppm or better. If I use an external 40 MHz crystal with 1 ppm accuracy will the APB clock now have 1 ppm accuracy? Is the APB clock derived directly from the external 40 MHz crysta...