Android (mostly 7) is misbehaving on BLE connect

Hi,

our BLE device has a hard current limit around 1mA. This is no problem as long as the BLE central behaves as "intended", e.g. iPhones use mostly connection intervals of 30ms which will respect the 1mA current limit. Also most Android devices obey to the peripheral connection parameter suggestions, although they use odd numbers. So no problem here.

But other Android (7?) devices behave differently: they do a connect with harmless parameters, but after a while (1s or so), out of the blue they switch to a fast connection for around 500ms. Connection interval in this case is always 7.5ms. Those 500ms are Android device dependent and also seem to depend on mood of the Android device.  Needless to say, that this breaks our current limit.

I've already tweaked with local slave latency, tuned TX power down, checked here, checked there. To no avail... :-(

Does anybody has any suggestions how to reduce the actual power consumption of the nRF5x peripheral device? Would be great, if (local) slave latency would work, or if there would be an API to set the minimum allowed connection interval.
Or is there a way to use the Timeslot API to suppress BLE intervals?

Thanks for help

Hardy

PS: googling around showed this: https://stackoverflow.com/questions/47491493/android-ble-requestconnectionpriority-not-working, especially "Android temporarily changes connection interval to 7.5 ms during the GATT service discovery".  Don't know if this is correct.  But if yes, how to slow down the nRF side?

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  • Hi,

    This sounds like your Android device is trying to balance speed and power consumption. It does this by using faster connection intervals when it knows that a lot of data is about to be transmitted so that the transfer completes faster. Then, after the intensive data transfer is completed, the connection intervals are relaxed again to save power. A typical scenario is that the Android device enforces fast intervals during the connection process and service discovery, and then throttles down afterwards (as far as I know Apple devices don't use this mechanism). 

    In BLE the connection parameters are ultimately enforced by the central (your Android device). The min and max parameters you set in your peripheral application is just your preferred values and the central may chose to reject them. Furthermore, different Android devices ships with different chipsets and BLE stacks, which may behave and perform differently. 

    There is nothing you can do with TX power or timeslot API to change this. The change needs to be made on the Android side. 

    Here are two relevant threads:
    High BLE activity for 15 seconds after connection
    Questions about connection interval negotiation

    May I ask what it is that limits your current consumption to just 1mA?

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