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Free RTOS - strange behavior on Cortex-M3.

Posted by ravikiranhv on April 26, 2017

Hello experts,

I am working on freeRTOS V9.0 on Cortex M3. I have two application threads and 2 interrupts. Both the threads blocks on event which are posted by interrupts (I am using API ending with ISR from interrupts). Evevryting works fine if I have multiple thread and a single interrupt. Have multiple randomobservation on my setup on each boot.
Case-1: System hangs after starting RTOS. Both threads and Interrupts not working Case-2: Threads are not running but both the interrupts working ! Case-3: Threasds start running automatically after some time (about 60 seconds) after 10/20 interrupt processing Case-4: Everything works fine without any problem

I understood freeRTOS configuration requirement for interrupts from here and everything looks fine ! http://www.freertos.org/FAQHelp.html http://www.freertos.org/a00110.html#kernel_priority

Appreciate your bvaluable feedback :)


Free RTOS - strange behavior on Cortex-M3.

Posted by edwards3 on April 26, 2017

Do you have configASSERT() defined? Which M3 are you using and what is configMAXSYSCALLINTERRUPT_PRIORITY set to?

Free RTOS - strange behavior on Cortex-M3.

Posted by ravikiranhv on April 27, 2017

Yes configASSERT() is defined. Our Cortex M3 implements 3 bits(MSB) for priority configMAXSYSCALLINTERRUPTPRIORITY (191) //(i.e. priority 5). configKERNELINTERRUPT_PRIORITY (240)

Both ISR's calling free RTOS API's are set to priority 240.

Please suggets if I am missing anything.

Thanks in advance

Free RTOS - strange behavior on Cortex-M3.

Posted by rtel on April 27, 2017

240 is actually using 4 bits, but that shouldn't matter because the unimplemented bit will be ignored anyway.

Can you please say which chip you are using - if it is an STM32 then you also have to explicitly tell it not to sub-divide the priorities. Are you 100% sure it has three priority bits defined? We have had incidents where documentation on this has been wrong, which is why the head revision Cortex-M code in SVN has additional asserts() to actually measure this to determine if the configuration file settings are correct.

Free RTOS - strange behavior on Cortex-M3.

Posted by ravikiranhv on April 29, 2017


Thanks for the inputs.

I am using Max32550 controller from Maxim with 3 bit priority implementation.

Please suggest how to go about.

Appreciate your help

Free RTOS - strange behavior on Cortex-M3.

Posted by rtel on April 30, 2017

Try setting configKERNELINTERRUPTPRIORITY to 224, and if that does not help, update to the latest version of port.c, which contains more configASSERT() statements. Link assumes GCC, and the new asserts assume either _NVICPRIOBITS or configPRIOBITS is set to 3 in FreeRTOSConfig.h: https://sourceforge.net/p/freertos/code/HEAD/tree/trunk/FreeRTOS/Source/portable/GCC/ARM_CM3/

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