I want to know priority of Cortex-M3 processor

Thank you! your guide

your comment is helpful for me.

If you don't mide, I want to you to look at my code.

for instance

I'll control priority level like below

    uint32_t priorityGroup;                                     /* Variables to store priority group and priority */

    uint32_t priority;

    NVIC_SetPriorityGrouping(2);

    priorityGroup =  NVIC_GetPriorityGrouping();

    priority = NVIC_EncodePriority(priorityGroup, 0, 0);  //  preempt priority group , subpriority
    NVIC_SetPriority(TIMER0_IRQn, priority); 
   
    priority = NVIC_EncodePriority(priorityGroup, 2, 0); 
    NVIC_SetPriority(SysTick_IRQn, priority);  

I think that TIMER0_IRQn's priority level is become 0 and SysTick_IRQn's priority level is become 4.

With kind regards, yours

Thank you! your guide

your comment is helpful for me.

If you don't mide, I want to you to look at my code.

for instance

I'll control priority level like below

    uint32_t priorityGroup;                                     /* Variables to store priority group and priority */

    uint32_t priority;

    NVIC_SetPriorityGrouping(2);

    priorityGroup =  NVIC_GetPriorityGrouping();

    priority = NVIC_EncodePriority(priorityGroup, 0, 0);  //  preempt priority group , subpriority
    NVIC_SetPriority(TIMER0_IRQn, priority); 
   
    priority = NVIC_EncodePriority(priorityGroup, 2, 0); 
    NVIC_SetPriority(SysTick_IRQn, priority);  

I think that TIMER0_IRQn's priority level is become 0 and SysTick_IRQn's priority level is become 4.

With kind regards, yours

Hi Kyujin,

In your code you set the priority group setting to 2, so bit [7:3] is group priority / pre-empt priority, and bit [2:0] is sub priority.

Next the question is how many bits are implemented in the priority level registers. This is device specific, for example, with STM32F4 you have got 4 bits, so only bit [7:4] are implemented.

For minimum you have have 3 bits, where bit[7:5] are implemented.

When you execute NVIC_EncodePriority, the function take account of both priority group setting and implemented priority bit width. So if you are running this on a STM32F4, the function know that only bit [7:4] are available, and all of this is for group priority / pre-empt priority, so it set encoded SysTick priority value to 2 (no subpriority bits).

Assumed you have 6 bits of priority level, then your table for NVIC_EncodePriority is correct (but I changed the labels and table layout slightly to make it clearer):

  priority = NVIC_EncodePriority(priorityGroup, group priority, sub-priority)

Now if run the same code on a device with few priority level bits, e.g. STM32F4, there will be no sub-priority if you set PriorityGroup to 2, so you end up with:

I hope this helps. It might be easier to understand this if you have actual hardware to run a test, and use single stepping or printf to examine the results for each step.

I am on a business trip next 10 days so won't be able to do anymore reply at this stage.

regards,

Joseph

your comment as above is very useful for me.

so. I understood very much about priorities.

thank you~

With kind regards, yours