WFE vs WFI (Rak8211 - nRF52)

[espruino-discuss]

Posted at 2018-12-17 by Nadnerb

I was going through the Espruino Source code and noticed that the sleep uses WFE instead of WFI for the nrf52

It was my understanding that WFI is typically used for standby and WFE is used for spinlocks. Just wondering what the benefit of using WFE is in this instance, and if we can get more power savings by using WFI if we are sleeping for a long period of time with an Interrupt wake-up source?

[gfwilliams]

Posted at 2018-12-18 by @gfwilliams

It's just what sd_app_evt_wait uses, which is what Nordic use in their SDK.

My understanding is that with the Nordic Softdevice you have to use WFE - at least that's what I found mentioned on Nordic Devzone. I could be wrong though?

You'll see there's some code around there to go back to sleep immediately if nothing has come in for Espruino - but I believe that a lot of the time IRQs get fired in the softdevice to handle the radio side of things