WFE, interrupt latency and flash start up time

[Niels Jorgensen]

Hi all,

In order to lower the power consumption of my device I have been experimenting with WFE. When using WFE I see that the interrupt latency is increased from ~4µs to ~14µs in my application (timer interrupt). In

https://devzone.nordicsemi.com/f/nordic-q-a/17163/interrupt-latency-on-nrf52

and

https://devzone.nordicsemi.com/f/nordic-q-a/15890/interrupt-latency-when-running-wfi-wfe

it is stated that the flash startup time adds approximately 7µs to the interrupt latency when using WFE. In order to reduce the interrupt latency I have also tried to enable constant latency and in my case the interrupt latency dropped to ~13µs. However, I would like to reduce the interrupt latency even further. Thus, I tried moving functions in the interrupt service routine from flash into RAM. Unfortunately, it is not possible to fit in RAM. Hence, my next idea is to avoid the flash start up time by keeping the flash on during WFE. If it is possible? I know that it would be at the expense of increased power consumption. But I can't find any way to keep the flash on, but I hope that someone can help me achieve this.

Thanks in advance,

Niels

[Stian Røed Hafskjold]

Hi, unfortunately it's not possible to keep the flash on in system on idle mode (WFE).

[Niels Jorgensen]

Thanks for the feedback Stian. Unfortunately, not the answer I was hoping for

[Stian Røed Hafskjold]

I understand it wasn't the answer you were hoping for, but I think the solution here is to execute the time critical parts of the code from RAM. You say that you can't fit the code in RAM, but if you only move the code with critical timing is it still too small?