freertos priority confusion

RE: freertos priority confusion

Dave_couling — Wed, 30 Aug 2017 19:57:20 GMT

So its good practise to set the Timer task priority very high. For example #define configTIMER_TASK_PRIORITY ( 5 )

This would allow me to call HVX or any softdevice API call within the timeout handler?

RE: freertos priority confusion

Susheel Nuguru — Wed, 30 Aug 2017 08:25:15 GMT

The task prirorities of freeRTOS are not same as interrupt priority. FreeRTOS internal house keepingis done in RTC interrupt context and the task is executed in PenSV interrupt context. All the task priorities are internal to FreeRTOS scheduler which is just uses a scheduling algorithm to select which task to run, so the task priorities in FreeRTOS are not hardware controlled. Like I said, Any OS cannot say that it has this priority scheme for ARM core and different priority scheme for others, that will make the application completely non portable between cores.

RE: freertos priority confusion

Susheel Nuguru — Wed, 30 Aug 2017 08:09:45 GMT

"The next thing to know is that, in ARM Cortex-M cores, numerically low priority values are used to specify logically high interrupt priorities. For example, the logical priority of an interrupt assigned a numeric priority value of 2 is above that of an interrupt assigned a numeric priority of 5."

This is meant for ARM cores, hardware, not for FreeRTOS. An OS cannot make priority mean different for different cores, that will be super confusing. I agree that in the post you referred where i said it wrong too, but bigzero corrected me.

RE: freertos priority confusion

Dave_couling — Wed, 30 Aug 2017 00:28:43 GMT

Another question on this topic would be, my SAADC callback is set to interrupt priority of 6 (same as RTC). How does this translate to the SDK interrupt priorities?

Since the callbacks are technically interrupts, if I want to unlock a Semaphore do I have to use the xSemaphoreGiveFromISR() version?

Same question with an xTimer Starting and Stopping from an SAADC callback?

RE: freertos priority confusion

Dave_couling — Tue, 29 Aug 2017 22:10:06 GMT

Also contradicts what you stated in this thread: devzone.nordicsemi.com/.../

RE: freertos priority confusion

Dave_couling — Tue, 29 Aug 2017 17:45:22 GMT

This contradicts the FreeRTOS documentation. In file list.c "...on Cortex-M parts where numerically high priority values denote low actual interrupt priorities, which can seem counter intuitive."

This is also mentioned in the FreeRTOS documentation page: www.freertos.org/RTOS-Cortex-M3-M4.html

RE: freertos priority confusion

Susheel Nuguru — Tue, 29 Aug 2017 09:20:42 GMT

Hi Dave, In FreeRTOS low priority number means low priority (inverse to what we have on ARM core, where exception priority is higher with lower number).

You can read more about FreeRTOS priority here. Please note the line below mentioned on that page.

Low priority numbers denote low priority tasks. The idle task has priority zero (tskIDLE_PRIORITY)

I haven't tried the example in SDK14 myself but quick look shows that the function nrf_sdh_freertos_init creates a task for BLE.