rtel wrote on Friday, December 22, 2017:
I think it is only the PenSV that needs to run at the lowest priority,
it is just recommended to run SysTick at the lowest too to leave a lot
of higher priority interrupts available for applications that require
them to be more real time (deterministic). Some libraries (STM32Cube?)
poll the tick inside an ISR (not good practice in my humble opinion) in
which cases having the tick at the lowest priority can actually cause a
deadlock. It is also generally more efficient if the tick is only
incremented after other interrupts have completed, rather than intermix
ISRs that are using the time and having the time changing.