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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 (http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0337e/ch05s03s02.html), 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)?



 

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