Unable to talk to IOS11 phone

[anealca]

I have a startup sequenced (nRF52832 peripheral) based on the s132 (v7.0.1 BLE 5.1) NFC Pairing example where it advertises at 1Msps link rate, then uses the PHY UPDATE API to go to 2Msps.  My peripheral node works correctly when using an nRF dev board for the Central node and getting the central node to request the PHY UPDATE. 

Our code on older Apple devices (IOS6), which do NOT request the PYH UPDATE, works correctly leaving the link at 1Msps.

When I try to connect to an IOS11 Apple IPhone or IPad as the central node (using the same Central node code), I see them request the PHY UPDATE to 2Msps.  My peripheral device accepts the update and seems to complete it correctly (the action is successful using my Central node).

BUT

What I see is after the link speed has changed, is that the Apple devices stop all communication and the link times out.

I get  no GAP, GATTC or GATTS events or errors on my peripheral device until the timeout.

Ideas? Debugging hints? Thoughts?

[Kenneth]

Hi,

I suspect we need an on-air sniffer log (e.g. using nRF sniffer) to see what is actually occurring here. However if you suspect it is related to RF_PHY update, you can check if you may be calling sd_ble_gap_phy_update() somewhere in the application on the peripheral outside of the BLE_GAP_EVT_PHY_UPDATE_REQUEST event.

Kenneth

[anealca]

I know I am not calling the update request ftn from the peripheral except in that event...

The problem with the sniffer logs is it doesn't switch to 2Msps. So the sniffer stops recording as soon as they switch to the higher link speed.  I do not know how to get the sniffer to also switch to 2Msps.  

[Kenneth]

If you are using the latest nRF sniffer with an nRF52-DK you should be able to also sniff 2Mbps I believe:
https://www.nordicsemi.com/Software-and-tools/Development-Tools/nRF-Sniffer-for-Bluetooth-LE

Is that what you are doing?

Can you share the sniffer log before switching to 2Mbps?

[anealca]

It turns out that iOS10 and newer requires the use of an MTU size of 185. This is concerning since BLE certification expects the normal MTU size.