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NVIC Priority Groups

Question asked by Joshua on Apr 7, 2014
Latest reply on Apr 7, 2014 by Clive One
I have read through Yiu's Cortex M3 book on the NVIC, and read this section of the COrtex M3 manual (, and am still missing the answer to one vital, basic question: does the Priority Group have any bearing on the actual priority assigned to an IRQ, or do the groups just allow you to have available different numbers of preemptive priorities/subpriorities?

So for example, if I want 16 subpriorities, I have to use Group 0, as its the only group with 4 bits available for subpriorities. 

But if I've assigned an IRQ to Group 0, subpriority 0, is this necessarily higher than one assgined to Group 1, pre-emption priority 0, subpriority 0? If not, how are these arbitrated? 

EDIT: Or, do I assign a Preemption Priority to a particular group (which could be any of the four), and the IRQs that are then included in that group would all have the same preemption priority (but possibly different subpriorities)?