Nested CRITICAL_REGION_ENTER/CRITICAL_REGION_EXIT

[RK]

Are you supposed to be able to nest critical regions using CRITICAL_REGION_ENTER and CRITICAL_REGION_EXIT? Here I mean you have a function which uses a critical region to surround some work, and you call that function from within another critical region set up by another function. So you end up calling CRITICAL_REGION_ENTER twice, then CRITICAL_REGION_EXIT() twice.

Looking at the code for CRITICAL_REGION_ENTER, it makes sense. If the softdevice isn't enabled, it just turns interrupts off, else it relies on the softdevice to have turned off the application ones. However the code for CRITICAL_REGION_EXIT doesn't make so much sense. It's here..

#define CRITICAL_REGION_EXIT()                                                              \
        if (CURRENT_INT_PRI != APP_IRQ_PRIORITY_HIGH)                                       \
        {                                                                                   \
            uint32_t ERR_CODE;                                                              \
            __enable_irq();                                                                 \
            ERR_CODE = sd_nvic_critical_region_exit(IS_NESTED_CRITICAL_REGION);             \
            if (ERR_CODE != NRF_ERROR_SOFTDEVICE_NOT_ENABLED)                               \
            {                                                                               \
                APP_ERROR_CHECK(ERR_CODE);                                                  \
            }                                                                               \
        }                                                                                   \
    }

This calls __enable_irq() directly, thus immediately turning on all interrupts so the critical region is effectively ended at this point even if you were nested and sd_nvic_critical_region_exit() was not going to disable the interrupts.

Should the code not do the inverse of the CRITICAL_REGION_ENTER() code and only call __enable_irq() in the case the softdevice isn't active? Something like

   #define CRITICAL_REGION_EXIT()   
            if (CURRENT_INT_PRI != APP_IRQ_PRIORITY_HIGH)  
            {     
                uint32_t ERR_CODE= sd_nvic_critical_region_exit(IS_NESTED_CRITICAL_REGION);
                if (ERR_CODE == NRF_ERROR_SOFTDEVICE_NOT_ENABLED) 
                { 
                    __enable_irq();  
                }
                else 
                {   
                    APP_ERROR_CHECK(ERR_CODE);  
                }  
            }   
        }

Or do you have to ensure that you never call functions which end up nesting critical regions like this?

[John]

From examining the SDK documentation on the macros and the soft device critical region functions, you cannot nest the critical regions using the macros. You can if you call the soft device functions yourself and manage the is nested flag yourself. As for the exit macro implementation, I'm not knowledgeable enough to comment.