We've been doing some long-term power consumption testing of our product with the Nordic PPK2 — which is a fantastic tool — and have discovered an anomalous increase in BLE current draw after our system is running in steady-state for about six hours. We think it's very clear this being caused by a change in behavior of the S113 SoftDevice, perhaps due to some interaction with the iPhone 11 Pro running iOS v17.4.1 that we used for the test.
Specifically, about six hours into a ten-hour overnight test, we see an abrupt and persistent change in BLE current draw, increasing from about 180 uA in the first six hours to a new mode which features long (e.g. 10 minute) periods in which BLE current draw is about 550 uA. Because this change happened in the middle of the night -- roughly six hours after the iPhone went to sleep mode, at a time when there was no interaction with the IPhone or the test device -- and because it does not appear to be correlated with an increase in BLE traffic from our mobile app, it appears to be a change in behavior of the S113 SoftDevice, perhaps due to some interaction with iOS.
Is Nordic aware of such an issue? What could cause the S113 to change its behavior and increase its current draw so dramatically? What can we do to prevent or remedy this if it occurs?
I have attached a PDF showing six screenshots from this ten-hour PPK2 capture. The first three show what we typically are seeing and expect during fast-advertising and for the first six hours of our test after successful connection and pairing. The last three show the sudden and persistent change in behavior that featured long periods of high BLE current draw for the last four hours of our test.
One possibility we considered was that somehow the S113 was disconnecting and entering fast-advertising for reconnection for some reason. However, we log all such BLE state transitions, and no such transitions occur. To the best of our knowledge, the S113 should still have been connected to the iPhone. Also, this anomalous high current draw (e.g. 550 uA) is about 100 uA less than what we see during fast-advertising.
What is interesting, as shown in the last screenshot in the PDF, is that once we started interacting with the phone (but not our mobile app) in the morning, the anomalous high current draw did not disappear, but did change behavior, switching from long periods of high current draw to shorter bursts, but the overall high current draw was still persistent.
Thank you for your help!
