Understanding priority levels of ISR and FreeRTOS APIs

[aggarg (Gaurav Aggarwal)]

Thank you writing in detail. Your understanding is mostly correct, just a minor correction:

@likko-liu

During the execution of interrupt 5, all interrupts below MAX_SYSCALL_INTERRPUT_PRIORITY will be blocked, so the accident caused by the interrupt 4 preemption execution mentioned above will not happen.

The above is true when the FreeRTOS API explicitly enters a critical section by calling taskENTER_CRITICAL_FROM_ISR:

void FreeRTOS_API_FromISR( void )
{
    /* Priority 4 interrupt is NOT blocked here. */

    taskENTER_CRITICAL_FROM_ISR();
    {
        /* Priority 4 interrupt is blocked here because all the interrupts upto
         * configMAX_SYSCALL_INTERRPUT_PRIORITY are blocked here. */
    }
    taskEXIT_CRITICAL_FROM_ISR();

    /* Priority 4 interrupt is NOT blocked here. */
}