I’ve been having fun with SysTick’s priority too!
It appears that, because it’s a ‘core’ function, it is described within PM0056 (15491 Rev 3), rather than RM0008.
Its priority is set by the PRI_15 field within SCB_SHPR3 (System Control Block, System Handler Priority Register) – see PM0056 p139.
It would seem that altering the Group setting would affect it (and all other ‘system’ priorities), although I can’t find an explicit reference to this.
It defaults to 0x00 (highest possible priority), although a catch is that core_cm3.h: SysTick_Config() overrides it to 0x0F (read back as 0xF0), but without explaining why!
You can easily override it back by calling NVIC_SetPriority(), but I’m nervous about this – why did ARM think that it needed to be overriden to the lowest priority (or is this a bug…)?
Perhaps others know more?
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