Repeated connection interval updates on iOS 26

[nrbrook]

We have noticed an issue with our device built on nRF5 SDK + nRF52832 when connected to iOS 26.

Initially after connection, everything is ok. Then we attempt a connection parameters update. After this update, seemingly regardless of the parameters, iOS 26 gets stuck in a loop switching between 7.5ms and 15ms intervals. I have monitored the connection with PacketSniffer, and can't see any further requests after our initial request. I've attached the packet log. I've tried connection interval ranges of 7.5-15ms, 11.25-15ms and 15-15ms, all have the same effect. Also when the connection interval is later changed to 50-75ms, the updates continue.

This seems like an iOS bug and I will report it to Apple, but I wondered if Nordic might have any insight?

Packet log attached.

packetlog.pklg

[Turbo J]

Does your device expose HID service?

Those get different connection intervals on iOS, and may cause the central to switch to low latency connection parameters. I believe this is documented by apple somewhere.

[nrbrook]

Yes it does. Apple's guidelines from developer.apple.com/.../Accessory-Design-Guidelines.pdf

General connection parameter request guidelines:
● Peripheral Latency ≤ 30 connection intervals.
● Supervision Timeout from 6 seconds to 18 seconds.
● Interval Min ≥ 15 ms.
● Interval Min ≤ 2 seconds.
● Interval Min is a multiple of 15 ms.
● One of the following:
● Interval Max at least 15 ms greater than Interval Min.
● Interval Max and Interval Min are both 15 ms.
● Interval Max * (Peripheral Latency + 1) of 6 seconds or less.
● Supervision Timeout greater than Interval Max * (Peripheral Latency + 1) * 3.
If Bluetooth Low Energy HID is one of the connected services of an accessory, a connection interval
down to 11.25 ms may be accepted by some devices.
Note:
When Interval Max and Interval Min are both 15 ms, some devices (such as Apple Watch) will
offer a 30 ms interval to better balance power and performance constraints.

As mentioned, I tried using a variety of intervals, all have the same issue. I've checked all calls to sd_ble_gap_conn_param_update, we aren't calling it repeatedly, and also the packet trace shows all updates are coming from iOS side. This doesn't happen in previous iOS versions

[Amanda Hsieh]

nrbrook said:

This doesn't happen in previous iOS versions

Please contact the Apple support team for help.