nRF9160 excess power consumption after RTT disconnect

[JordanYates]

After connecting to an nRF9160 using SEGGER tools (J-Link RTT Viewer v7.62b), excess power consumption is observed until the device is reset (via `nrfjprog -r`)

First the board is using a low amount of current, after RTT connects more power is used, but after disconnecting the consumption does not return to the original value.

The image below show the sequence.

I suspect that the DWT hardware block is not being correctly powered down on the disconnect. This issue does not occur on nRF82840 designs.

[helsing]

Hi Jordan, sorry for the delay.

When using the read function (for readregs, memrd etc.) in either nrfutil or nrfjprog, debug mode is then started and the cpu is halted. After reading out the data a reset is necessary in order to exit debug mode and start running again(with lower power consumption). 

More details on this can be found in the Debug interface mode section:

[JordanYates]

So the answer is that requesting power via `CxxxPWRUPREQ` fundamentally changes the internal power consumption of the SoC in a way that is not reversed by reverting the value written to `CxxxPWRUPREQ`, and can only be recovered through a pin reset.

[helsing]

Hi Jordan, sorry for the delay. 

JordanYates said:

can only be recovered through a pin reset.

The recommendation is to use pin reset or power cycle in the production line. This has been recommended in order to ensure that the SoC is not in any state with higher power consumption when leaving the production line. 

However, you can try with other types of reset, for example

$ nrfutil device reset --reset-kind RESET_SOFT

Hopefully, a soft reset works sufficently for everyday development.