Understanding priority levels of ISR and FreeRTOS APIs

[richard-damon]

@MasterSil

sorry but how does having an interrupt of a logically higher priority than configMAX_SYSCALL_INTERRUPT_PRIORITY corrupt the critical sections? Is the logic that you don’t want to interrupt the processor while a critical section is being executed hence why the kernel disables the interrupts? Also, doesn’t interrupt priority <= configMAX_SYSCALL_INTERRUPT_PRIORITY means logically higher priority given the NVIC priority levels?

When FreeRTOS is manipulation its internal structures, like a ready list, it needs to make sure that no one else is going to also try to manipulate the structure. It does this by disabling the interrupts at and below configMAX_SYSCALL_INTERRUPT_PRIORITY. If an interrupt has a higher priority (lower value) than this and does call a FreeRTOS function (and the assert is present to catch it), and that function manipulates the same structure, that can result in a corrupted data structure, things like a task being lost from the ready queue is a very real possibility.