Anyway of keeping the RTC block in nRF51822 going while device is in Reset, has crashed or powered off?

[Håkan Brink]

Hi, Is there anyway to keep the RTC going while in reset, device sw has crasched or in powered off mode or would I need an external RTC for this?

Is there any possibility of adding a backup capacitor to keep the internal RTC block alive?

Anyway of retaing the information in RAM during reset, I know it may sound a bit stupid but if the device has crashed you may want to be able to write the last valid data to flash when device has been reset.? or for debug purposes..

BR, Håkan

[Ole Morten]

There isn't any magic way to keep only the RTC running, no. As section 11.1.7.8 in the Reference Manual shows the peripherals are reset on all types of reset.

As for keeping RAM over reset, you can see from the same table that RAM isn't reset on a soft reset, so it won't automatically be cleared. However, most standard libraries will clear all static ram in their reset handler, so to keep data, you have to make sure this isn't done on the areas you're interested in. Take a look at this for details.

[Håkan Brink]

Thank you , a follow up question:

If device is being RESET will all GPIOs revert to Off-state or, tristate(input buffer disconnect)? I use one of the GPIOs as an OE signal to a regulator and I would still like to have it enabled even if I do a Reset or the Watchdog has timed out and resets the device. I only want to release it when I do a normal poweroff. From what I can see in chapt.13 of nRF51 it seems not possible but at the same time config registers could be retained GPREGRET?

[Ole Morten]

Did you take a look at the table in section 11.1.7.8? As you can see there, the GPIO is reset on all kinds of reset, except for waking up from off mode, so the GPIO state will be reset also on a watchdog reset.

GPREGRET is just a register you can use to store custom data that you want to preserve over a reset. To use it, you'd still have to read it out and reapply the GPIO settings on reset, which timing-wise will cause a glitch on the IO.