Request more detailed SDK 15.2.0 peripheral interrupt priority change explanation

RE: Request more detailed SDK 15.2.0 peripheral interrupt priority change explanation

eric-appion — Fri, 22 Feb 2019 17:52:25 GMT

Hi Hung,

You are correct, we started with an earlier SDK. Thank you for the explanation. For my purposes it probably doesn't matter whether the SWI from the SoftDevice is above, below, or the same priority as the peripheral interrupts, because I've been careful to have all of the interrupt and event handlers do very little before returning; most of them just give a semaphore or post to a queue.

I've now changed the peripheral interrupts from 7 to 6 in our project to match SDK 15.2.0, and it seems to work fine.

Just to be clear about what I said regarding FreeRTOS, the defines I quoted are used to set the interrupt priority of RTC1, used for the FreeRTOS tick and scheduling.

Thanks!

Eric

RE: Request more detailed SDK 15.2.0 peripheral interrupt priority change explanation

Hung Bui — Fri, 22 Feb 2019 14:27:16 GMT

Hi Eric,

I would assume you were porting your application from earlier SDK to SDK v15.2 and then brought the configuration of peripheral interrupt priority to 7 from your previous application ?

In SDK v15.1 and earlier we have been setting the Softdevice SWI (the interrupt to send softdevice event to application) from 6 to 7 to match with the peripheral lowest interrupt priority level 7. So they have the same level. You can find the workaround in nrf_sdh.c in SDK v15.1 and earlier. However, in the workaround we missed S140 as at the time we though its SWI's default level was already 7. But it actually was 6.

So on SDK v15.2 we decided to remove that workaround and now everything is configured to level 6 including the application peripherals default interrupt.

In your case, you set your application interrupt priority level to 7, meaning your application interrupt can be pre-empted by the softdevice events.

If your application has no problem being preempted I don't see a problem here.

You are right about the FreeRTOS configuration, I would need to check with our FreeRTOS expert to see if there is any impact here.

RE: Request more detailed SDK 15.2.0 peripheral interrupt priority change explanation

Hung Bui — Fri, 22 Feb 2019 14:26:50 GMT

Hi Eric,

I would assume you were porting your application from earlier SDK to SDK v15.2 and then brought the configuration of peripheral interrupt priority to 7 from your previous application ?

So on SDK v15.2 we decided to remove that workaround and now everything is configured to level 6 including the application peripherals default interrupt.

In your case, you set your application interrupt priority level to 7, meaning your application interrupt can be pre-empted by the softdevice events.

If your application has no problem being preempted I don't see a problem here.

You are right about the FreeRTOS configuration, I would need to check with our FreeRTOS expert to see if there is any impact here.

RE: Request more detailed SDK 15.2.0 peripheral interrupt priority change explanation

eric-appion — Thu, 21 Feb 2019 20:42:20 GMT

It looks to me like FreeRTOS in the SDK examples is still using interrupt priority 0xf, which I assume is aliasing to 7. Should that also be changed to 6? These are the relevant lines from FreeRTOSConfig.h:

#define configLIBRARY_LOWEST_INTERRUPT_PRIORITY 0xf

#define configKERNEL_INTERRUPT_PRIORITY configLIBRARY_LOWEST_INTERRUPT_PRIORITY

RE: Request more detailed SDK 15.2.0 peripheral interrupt priority change explanation

eric-appion — Thu, 21 Feb 2019 20:39:39 GMT

Upon reading the SoftDevice Specification again, I see that the application is allowed to use interrupt priority 5. However, I still would like to know why the SWI required that the peripheral interrupt priorities change from 7 to 6.