[nRF52840] MPU FAULT: ISR taking too long ?

[AnomalySmith]

Hi,

I've got a GPIO interrupt callback that collects an ADC reading. All is fine until there.

But when interrupts become numerous (~3/5k triggers / sec), a MPU FAULT appears.

After some tests, I'm assuming it comes from the adc_read() (from Zephyr, <drivers/adc.h>) that takes too long inside the ISR callback and delayed next ISRs accumulate until it breaks. Testing by inserting only a delay inside ISR callback produce the same result.

Is there another way than postponing this task to consumer function ? Or, at least, could I know how much callback calls are waiting from the ISR so I could adapt temporarily avoid calling ADC (sort of mitigation process).

Thanks !

[Einarh]

Hello

I'm not sure if the adc_read() function is blocking, but if it is then you should avoid calling it in an ISR.

Instead you could try using adc_read_async(), or alternatively use a semaphore to signal from the ISR and call adc_read in your main thread.

Best regards,

Einar

[AnomalySmith]

Yes, finally I decided to change the logic even if it brings limitations in the final design.

Thanks.