Can services/characteristics/descriptors discovery could be made faster

RE: Can services/characteristics/descriptors discovery could be made faster

jpo38 — Mon, 09 May 2016 06:44:21 GMT

@dalida20893: Never tested on iOS. Sorry.

RE: Can services/characteristics/descriptors discovery could be made faster

dalida20893 — Thu, 05 May 2016 09:23:55 GMT

Hi, i have the same problem i tried the same solution but it doesn't work for me for iPhone, full services/characteristic/ descriptor is done in ~1200 ms, have you an idea why i have such a time ?

RE: Can services/characteristics/descriptors discovery could be made faster

jpo38 — Fri, 04 Dec 2015 15:23:18 GMT

Fantastic. Thanks a lot for all those clarifications.

RE: Can services/characteristics/descriptors discovery could be made faster

RK — Fri, 04 Dec 2015 15:17:49 GMT

just power consumption - and you can always change the connection parameters after you've done the initial service discovery if you like. As a peripheral you can request a change, as a central you can require one. The BTLE protocol is well-designed and allows for connection parameters to be changed as the connection moves into different stages. It's not uncommon to start a connection up on a higher power, low connection interval, no slave latency basis to get the service discovery done quickly but then allow it to drop back to something much lower power.

RE: Can services/characteristics/descriptors discovery could be made faster

jpo38 — Fri, 04 Dec 2015 14:53:08 GMT

@Anders: It's running on PC. See my answer, I changed to 10ms, I'll try 7.5 ms but 10ms is already fast enough as it challenged Android performances!

RE: Can services/characteristics/descriptors discovery could be made faster

Anders Strand — Fri, 04 Dec 2015 14:51:39 GMT

Are you running the central code on the PC, or on the Dongle? You can choose connection parameters when you connect to the peripheral using sd_ble_gap_connect. Update the p_conn_params struct with 7.5 ms max and min inerval before connecting.

RE: Can services/characteristics/descriptors discovery could be made faster

jpo38 — Fri, 04 Dec 2015 14:51:35 GMT

@RK: Got it. I changed connection min/max interval and it's now much faster (see posted answer below). I'm just wondering if changing those parameters present any risk of any kind...

RE: Can services/characteristics/descriptors discovery could be made faster

jpo38 — Fri, 04 Dec 2015 14:50:44 GMT

With RK help, I finally solved this.

On the application side (PC), I was keeping the connection parameters from Nordic example:

#define MIN_CONNECTION_INTERVAL          MSEC_TO_UNITS(30, UNIT_1_25_MS)
#define MAX_CONNECTION_INTERVAL          MSEC_TO_UNITS(60, UNIT_1_25_MS)

I changed them to:

#define MIN_CONNECTION_INTERVAL          MSEC_TO_UNITS(10, UNIT_1_25_MS)
#define MAX_CONNECTION_INTERVAL          MSEC_TO_UNITS(10, UNIT_1_25_MS)

Now, full services/characteristic/descriptors is done in ~400ms. It's even faster than what I have when using Android/Qt API!

Now, Im' not sure about the consequences of such a change....will it only impact my device power consumption? Or could it alterate data or performances...?

RE: Can services/characteristics/descriptors discovery could be made faster

RK — Fri, 04 Dec 2015 09:34:34 GMT

Half the connection interval/slave latency comes from the peripheral, other half from the central connecting. So first off you need to figure out which one is limiting the connection interval and you need to also see if there was slave latency set on the connection. You have both halves of that code so it should be quite practical to see what's set. Log it too - on connection you are given the actual parameters, dump them and see what you've got. Or sniff, you can see them in the connection packet.

Most likely reason the other thing is faster is because it negotiates a lower connection interval or no slave latency. Dump it or sniff it and see what you get. Interval goes down to 7.5ms, so you should be able to get a request/response pair in 15ms.

I've never seen anything manage to receive a response and send the next request same interval, sniff to see if that's happening too.

RE: Can services/characteristics/descriptors discovery could be made faster

jpo38 — Fri, 04 Dec 2015 09:10:43 GMT

"Some people reduce the connection interval" how can I do that? Can it be done on application side (PC/dongle)? How do you explain the fact that QtBluetooth API on Android goes 3 time faster with the same BLE device being connected?

RE: Can services/characteristics/descriptors discovery could be made faster

RK — Fri, 04 Dec 2015 09:04:28 GMT

What's your connection interval, looks like it's about 100ms? You only get one request/response per connection interval so if that's higher, it takes longer. Some people reduce the connection interval to a low value before connection so that service discovery is faster, then drop it back down later if such a connection interval isn't required.

And the 'few at a time' discovery API isn't going to get reworked, that's how discovery is specified in the bluetooth spec, max information which fits in a request, then a new request. The only thing which could change there is a higher MTU which currently isn't supported (it's not supported by many implementations).