Why I can not set connection interval to 7,5ms?

RE: Why I can not set connection interval to 7,5ms?

run_ar — Mon, 13 May 2019 08:16:27 GMT

I am sorry for the late answer. I don't think reducing the ppm value will enough to be able to reduce one unit, but it might. Eventually the Central will calculate how much time is needed, and choose an appropriate interval.

RE: Why I can not set connection interval to 7,5ms?

rolandash — Wed, 24 Apr 2019 14:44:46 GMT

thank you run_ar

I can understand that SD needs to prepare for worst case. Is there a way that I tell SD that condition is not that bad so I can use more tight timing?

For example, if I use a 20ppm LF XTAL instead of 500ppm RC, will that help SD to use shorter interval?

RE: Why I can not set connection interval to 7,5ms?

run_ar — Wed, 24 Apr 2019 13:38:18 GMT

For the peripheral links we also add time for the worst case window widening, calculated based on supervision timeout and LF clock ppm setting.

Not sure what the minimum is for 2 peripheral links and 1 central link, but remember that the link timing is controlled by two different clocks for central and peripheral, so you will get a few collisions regardless.

RE: Why I can not set connection interval to 7,5ms?

rolandash — Thu, 18 Apr 2019 17:35:36 GMT

Any further hints?

thanks.

RE: Why I can not set connection interval to 7,5ms?

rolandash — Sat, 13 Apr 2019 08:42:30 GMT

Please note that at 832 end, only 2 links are configured, and I still can not set min_interval to 6 units, sd_ble_gap_ppcp_set(&gap_conn_params) still returned error 7 invalid param.

The behavior is the same as the 840 side, seems not related to how many links been configured.

RE: Why I can not set connection interval to 7,5ms?

rolandash — Sat, 13 Apr 2019 05:39:31 GMT

run_ar

thanks.

I am not sure why you are saying 8 links? I only set 2 peripheral links and 1 central links on 840 side, in total it is 3. As each gap event length takes about 2.5ms, so 7.5ms seems good to fit.

Even if count in the pre/post processing time, then 10ms maybe be good enough? I am not sure what SD gives 11.25ms in the end?

RE: Why I can not set connection interval to 7,5ms?

run_ar — Fri, 12 Apr 2019 12:24:26 GMT

Hi,

Remember that the softdevice also need time for pre- and post-processing. See: Bluetooth Low Energy central connection processor usage

I would not expect to be able to handle 8 links within 7.5 ms. You can find more information on scheduling here: Connection timing as a Central