cortex m3 idle taks priority question !

boogalee wrote on Thursday, January 21, 2016:


finally i had succeed porting to my boad

and then i had created multiple tasks, and i got a questions.

FreeRTOS doc siad cortex m3’s priority is specially low value is high priority meaning.

and FreeRTOS setting’s priority of idle task was set 0. highest priority !

i had set my task’s priority 1,2,3… over 0.

then, idle task’s priority is top of all. here, is it possible to run other task ? becausen they have lower priority.

but… my program was run very well…

im very confusing… help me…


rtel wrote on Thursday, January 21, 2016:

You are confusing task priorities with interrupt priorities.

RTOS tasks are created by software and scheduled by software, and run when an interrupt is not running. Which RTOS task runs when is decided by software (the RTOS scheduler). In FreeRTOS the lower the task priority number the lower the task’s priority (which in my humble opinion is logical).

Interrupts will interrupt non-interrupt code, and which interrupt executes when is controlled by hardware. The RTOS software cannot influence how the hardware prioritises interrupts, in fact this is not really an RTOS question, no software can influence how the hardware prioritises interrupt. On ARM Cortex-M architectures (but very few other architectures) the lower the interrupt priority number the higher the interrupt’s priority (which in my humble opinion is illogical).

boogalee wrote on Thursday, January 21, 2016:

Thank you so much !!

yes. i just confued between Interrupt priority and task priority.

my setting was so natural result lol.

BTW, i had one more question about config.h’s two things.


if i define two things 0, and i set idle taks’s priority 0, other task which i made to 0

is it impossible to run other tasks ?

i had understad about upper configurations to 0, it can’t be preemptive & time slicing.

configIDLE_SHOULD_YIELD 1 allow time slicing.

what happened ?

other task is ruuning.


boogalee wrote on Thursday, January 21, 2016:

oh. i confused just preemptive and cooperative multitasking’s meaning.

Thanks anyway


rtel wrote on Thursday, January 21, 2016:

I think if configUSE_PREEMPTION and configIDLE_SHOULD_YIELD are both 0
then probably only the idle task would run - but its not a normal
configuration and I’ve not checked.

These settings do not control time slicing though, that is controlled by