Nexus 5X connection interval

RE: Nexus 5X connection interval

Wed, 20 Apr 2016 22:47:33 GMT

Emil: Thanks for the clarification!

RE: Nexus 5X connection interval

Wed, 20 Apr 2016 22:26:34 GMT

Hung Bui: What event do you look for when connection parameter negotiation fails?

RE: Nexus 5X connection interval

Wed, 20 Apr 2016 22:23:31 GMT

Emil: Looking at the Android source, it looks like the minimum is 9ms (ie, #define BTM_BLE_CONN_INT_MIN_LIMIT 0x0009). I am curious to know how you got 11.25ms.

RE: Nexus 5X connection interval

Hung Bui — Tue, 22 Mar 2016 14:59:56 GMT

I think one solution is to try to do connection parameter negotiation meaning you start first with low connection interval request, says 7.5ms, if that request gets rejected, you can try again with for example 15ms and so on. Doing that you will be able to achieve the lowest possible on different platform. Instead of sending only one request say 10ms and then end up with 45 ms because that request get rejected.

RE: Nexus 5X connection interval

shadow — Tue, 22 Mar 2016 07:59:16 GMT

Thank you Jan, The Nexus 5X supports 11.25ms connection interval.

RE: Nexus 5X connection interval

endnode — Tue, 22 Mar 2016 07:39:15 GMT

Hi Joy Kang,

All phones (Android, iOS and I suppose also any other rich OS) are primarily tested with one (or narrow range of) connection intervals in BT LE GAP Central role. Only once Google release mint Android FW for Nexus device with 7.5ms connection interval: very first (factory) image of Android 4.4 for Nexus 5. Since then they realized (obvious thing) that Central role doesn't scale in terms of parallel connections if you use very low connection interval values. So to be able to guarantee that core feature they fix it at 40~50ms range. Now even if you don't run more than one LE connection at a time these "low level" parameters of LE stack are fixed and not accessible from API exposed to your apps. And while it's not the best for throughput I believe it's good decision for interoperability reasons.

However you can find different forum posts and suggestions that if you fix PPCP (Preferred Peripheral Connection Parameters) on GAP Peripheral side with lower connection interval than 40~50ms, then some phones use as low interval as 20ms. Unfortunately there are cases (HW + OS build combinations) which simply drop connection under these conditions.

To summarize it: for particular phone (if you care only about one or few handsets with given OS release) you might be able to "force" lower intervals from GAP Peripheral side but unlikely very low values such as 7.5ms. In general you should rather accept default values in 40~50ms range.

Cheers Jan