Use shorter "instant" when updating Bluetooth LE connection parameters (LL_CONNECTION_UPDATE_REQ)

Originator:martijn
Number:rdar://21400457 Date Originated:16-Jun-2015 01:51 PM
Status:Open Resolved:No
Product:Hardware Product Version:
Classification:Enhancement Reproducible:N/A
 
Summary:
It seems that currently the Bluetooth controller in the iOS devices uses an "instant" of +13 connection events in the LL_CONNECTION_UPDATE_REQ link layer command.

Our accessory uses relatively long (let's say ~600ms) connection intervals to conserve energy. When the user interacts with the accessory, it requests a shorter interval to improve the responsiveness during user interactions. However, this takes 600ms * 13 = 7.8 seconds for such a change to take effect. This is unacceptably long.

The Bluetooth 4.0 specification prescribes a minimum of +6 connection events. This would decreases the delay to 3.6 seconds.

We started using the Slave Latency feature to overcome part of the delay. Using 4 as Slave Latency and 150ms as connection interval, a similar power profile is met. The cost of switching now is 150ms * 13 = 1950ms, which is still a noticeable delay for the user. If the minimum "instant" distance of +6 connection events would be used, the delay would be cut down to 150ms * 6 = 900ms.

Steps to Reproduce:
N/A

Expected Results:
N/A

Actual Results:
N/A

Version:
Tested on iPhone 5, iOS 9 beta 1

Notes:


Configuration:
Tested on iPhone 5, iOS 9 beta 1

Attachments:

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