SysTick vs. keeping an Arduino Due in Sleep mode

Official Hardware Mega Due
5

I found additional discussion on the matter - apparently the exact details of where SysTick is clocked from are "implementation dependent." Too bad that it doesn't seem very well documented in the implementation manual (ie SAM3X datasheet.) Sigh.

https://community.arm.com/processors/f/discussions/4946/why-or-how-does-systick-interrupt-wakeup-the-processor