FreeRTOS configLIBRARY_MAX_SYSCALL_INTERRUPT_PRIORITY

[WestCoastDaz]

I have a question about Nordic's implementation of FreeRTOS. In the FreeRTOSConfig.h the following is defined as:

   /* The highest interrupt priority that can be used by any interrupt service
routine that makes calls to interrupt safe FreeRTOS API functions.  DO NOT CALL
INTERRUPT SAFE FREERTOS API FUNCTIONS FROM ANY INTERRUPT THAT HAS A HIGHER
PRIORITY THAN THIS! (higher priorities are lower numeric values. */
#define configLIBRARY_MAX_SYSCALL_INTERRUPT_PRIORITY    1

The S132 SoftDevice Specification V2.0 Interrupt Model and processor availability indicate that interrupt priority 1 is reserved for SoftDevice memory protection.

Given that configLIBRARY_MAX_SYSCALL_INTERRUPT_PRIORITY will set the Cortex base priority to 1 should this interrupt be masked during critical section calls?

[RK]

It doesn't use the FreeRTOS API, nothing in Nordic's code uses the FreeRTOS API. It doesn't need to be masked but it doesn't really matter. That interrupt is only there to catch people writing to bits of memory they shouldn't from non-softdevice code and hardfault. Change it to 2 or leave it as 1, either works.

[WestCoastDaz]

RK, As always thank you for you comments!

In my mind to enforce the point that the SoftDevice memory protection doesn't use FreeRTOS API this should be set to 2 in future versions of the SDK.

[Susheel Nuguru]

Hi,

I think it should be set to _PRIO_APP_HIGH so that we do not forbid using FreeRTOS API in interrupt contexts. The same goes to BASEPRI

#define vPortRaiseBASEPRI( ) vPortSetBASEPRI(_PRIO_APP_HIGH << (8 - configPRIO_BITS))

I will communicate this with the developer