WDT and CRV

[Jonathan Swoboda]

Hi,

We are trying to configure the WDT and are running into issues. The plan was have a timeout of 30 seconds when running and then 24 hours when sleeping. Note we are also using the soft device with BLE advertising in the background. The device is support to be ultra low power so a long sleep time is needed. We also cant have a long expiry while running or we could burn a lot of power before the watchdog catches a bug. 

The problem is that CRV is not getting updated, the value stays fixed to the initial one. Is there no way to change it? If there isn't a way to change this that is going to be a big problem.

Note I also tried to pause the watchdog when sleeping but it still goes off. I assume soft device is running and the watchdog expires because the sd never feeds it. If that is case the WDT design seems very flawed and next to useless. 

Please advise,

Jon

[Carl Richard]

Hi, Jonathan! 

Thank you for reaching out.

---

The problem is that CRV is not getting updated, the value stays fixed to the initial one. Is there no way to change it? If there isn't a way to change this that is going to be a big problem.

As stated in the WDT documentation: The watchdog must be configured before it is started. After it is started, the watchdog’s configuration registers, which comprise registers CRV, RREN, and CONFIG, will be blocked for further configuration. This may be what is hindering you from updating CRV.

---
It is correct that the SD won't feed the watchdog. We recommend using a timer to wake up and feed the WDT in main at appropriate times, as stated here and here. 

Best regards,
Carl Richard

[Jonathan Swoboda]

Hi,

Thanks for the reply. A timer does not sound workable. If we want a 30 second timeout that means we have to have a timer go off every 30 seconds. We need the battery to last for years and this a huge waste of power and is not an acceptable solution. So just to confirm nrf_pwr_mgmt_run will not return every time soft device runs? The watch dog design seems to be very problematic.

Thanks,

Jon

[Carl Richard]

Hi again, Jon.

I'm afraid that the recommended solution, if the SD is active during sleep(f.ex. advertising), is to have an app_timer feeding the WD. The RTC is running anyway (because of the SD) so this should not have a significant impact on power consumption. 

You are correct that nrf_pwr_mgmt won't return on advertising events. For this you can use radio notifications as described in this tutorial (it's old but it should still work). 

Best regards, 
Carl Richard