nRF52832 Advertising Interval

[John]

I've been puzzled after looking at the current draw figures for the nRF52832. If the advertising interval is supposed to be 20ms.

Can someone explain why the advertising event is actually 25ms?

Or why the advertisng is added to the interval?

[John]

No I understand the "jitter" that you refer to. We have been working with TI and their timing is slightly different...not that it really matters. I'm just curious.

What they do is set the interval say 100ms, advertise at the start of the interval and deduct the time of the advertisement approx 4ms from the 100ms to calculate the sleep current which is then added to the total current over 100ms. What Nordic do is actually add the time of the event to the advertising interval so 100ms becomes 105ms. Just different..no problem working with it....I'm wondering if strictly speaking it conforms to the iBeacon specification with this very slightly different timing.

[FormerMember]

If the advertising interval is set to 20 ms, the device should advertise in the beginning of each interval each 20 ms.

How do you measure the 25 ms?

How do you set the advertising interval in your code?

[John]

The stack is supposed to add a random delay between 0 and 10mS to each advertising interval to help minimize collisions. There is a good explanation of advertising here:

Advertising explained

[RichieJH]

Thanks for the paper John. I'm too lazy to dig deeper and the paper doesn't mention it, but is that randomness set on the first advertisement and doesn't change or is it randomised for each and every advertisement?

[John]

This is from the 4.2 core specification: "The advDelay is a pseudo-random value with a range of 0 ms to 10 ms generated by the Link Layer for each advertising event."