I am trying to use systick counter to verify the accuracy of my RTC. Bascially what I did is check the systick counter against RTC timer in the second interrupt. I find it seems the systick count is heavily affected by other interrupts and not accurate. In the end I changed to use DWT cycle count and the result is fairly good and stable. Here my question is how the Systick counter is updated (I'm fairly new to embedded development)? I thought it is not driven by interrupt. The reason I thought like this is if I use TIMX and don't enable its interrupt. The counter of TIMX is pretty accurate.