GPIO wakeup from system OFF under FreeRTOS restarts at address 0x00000A80

RE: GPIO wakeup from system OFF under FreeRTOS restarts at address 0x00000A80

Susheel Nuguru — Thu, 12 Dec 2019 15:30:52 GMT

Brian,

The emulated SYSTEM_OFF mode and the emulated wakeup from RAM_RETENTION memory might not go well together.

[quote user="bfriedk1"] I found that if I press the reset button instead of the sense button the first time I run the app, I can then press the sense button after the next SYSTEM_OFF and I don't end up in the hard fault handler.[/quote]

This makes sense. The pin reset or the reset button should bring the device out out of debug mode. And hence the SYSTEM_OFF mode will not be emulated there after. And that explains why there are no hardfaults after pressing the reset button.

Like you already figured out, I do not think this is going to affect your actual release version of your product. It is just that the SYSTEM_OFF + RAM_RETENTION (emulation) are not designed to work together with the debugger.

RE: GPIO wakeup from system OFF under FreeRTOS restarts at address 0x00000A80

bfriedk1 — Thu, 12 Dec 2019 02:02:42 GMT

Susheel -

Thank you for the quick reply and additional details. Much appreciated. I wasn't aware that system OFF mode was emulated in debug mode, though that does make sense.

I also now see that the ram_retention example enters an infinite loop after calling SYSTEM_OFF mode. I did the same in my application, but unfortunately I am still ending up in the hard fault handler after pressing the sense button. After some experimentation I found that if I press the reset button instead of the sense button the first time I run the app, I can then press the sense button after the next SYSTEM_OFF and I don't end up in the hard fault handler. Our test app repeatedly enters SYSTEM_OFF after a delay.

Because the ram_retention app doesn't have this behavior, I suspect the failure is due to our app running under FreeRTOS. The SYSTEM_OFF is called from a FreeRTOS task. Are there additional calls required to achieve the same behavior as the ram_retention app from debug builds running FreeRTOS?

I do understand that release builds should behave properly. We are working towards getting our release build up and running. Just a little concerned that the behavior we are experiencing is different under FreeRTOS.

Regards,

Brian

RE: GPIO wakeup from system OFF under FreeRTOS restarts at address 0x00000A80

Susheel Nuguru — Wed, 11 Dec 2019 12:19:49 GMT

The System OFF mode does not work in debug mode. It is just emulated as mentioned here.

So it is recommended that if have an infinite while loop just after calling the SYSTEM_OFF mode in your application. That way when you start your program in debug mode, the instructions after the SYSTEM_OFF call are also executed. Most likely in your application the main function is exited causing the CPU to execute illegal instructions causing hardfault. Address 0x00000A80 seems to be the hardfault handler address inside the MBR in the softdevice.

but in non debug mode, the instructions after the SYSTEM_OFF call are never reached.