Modifying beacon advertising data while advertising

[JordanK]

I'm developing a broadcast advertiser (non-connectable, non-scannable) on an nRF52833 with the S113 SoftDevice, and am working from the Beacon Transmitter Sample Application example.

I would like to make it so that prior to each advertisement, it dynamically computes some values and includes those in the advertisement data (manufacturer-specific data). For example, let's say that I'd like to include in each advertisement the number of seconds that the beacon has been operational since it was last reset (i.e. a constantly-changing value).

So, I have two questions:

1. Is there a way to add a "hook" (or an event handler) that is triggered immediately before the advertisement is transmitted? This seems like it would be the ideal place to do such calculations. I took a look through the various events, thinking I might be able to do this on the event handler, but I can't find an event that corresponds to pre-advertisement-transmission. If there is no such hook/event, any recommendations on the best way to do this?
2. What is the proper way to update the advertised data without stopping/restarting the advertising? The sd_ble_gap_adv_set_configure function seems like the right one, but it's unclear how to use it while the advertising is still running, without accidentally corrupting the data being transmitted or ending up with a memory leak where old buffers aren't freed.

[JordanK]

I managed to get it working with a timer that calls the sd_ble_gap_adv_set_configure function on a fixed interval. I ended up preallocating two data structs and switching between them each time I updated the data (i.e. set the new data in the struct not being used, then call sd_ble_gap_adv_set_configure with that struct). Important note for other users: when calling sd_ble_gap_adv_set_configure after it's already been called, the `p_adv_params` argument must be `NULL`.

I'm still looking for a solution to question (1) though (a hook to update the data immediately before transmission), so if anyone has an idea for that, it would be much appreciated!

[Hung Bui]

Hi Kyle, 
Regarding 1, there isn't a softdevice's event that signal when an advertising packet is about to send. However, you can think of using radio notification. It's the event that you can set up so that the softdevice can signal the application when the radio is about to start or when the radio session is about to finish. 
You can read about it here: https://infocenter.nordicsemi.com/topic/sds_s132/SDS/s1xx/radio_notif/radio_notification.html?cp=5_7_3_0_10

However it can not tell you what kind of activity it's doing, only tell if it's doing TX or RX. So if you have a complex application (connection/multi connections and advertising at the same time) it would be difficult to keep track of which activity it's going to do.

However, if  you simply do non-connectable advertising, it shouldn't be to hard to keep track. 

[JordanK]

Hi Hung Bui ,

This is really interesting. In the time since I posted this question though, we've actually moved to the nRF Connect SDK, which doesn't have the concept of a "softdevice" anymore. Are you familiar with any way to achieve the same objective in nRF Connect?

[Hung Bui]

Hi Jordan, 
Yes we have similar concept for radio notifications in nRF Connect SDK. Now it's moved to MPSL module since the Softdevice doesn't exist. 
https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrfxlib/mpsl/doc/radio_notification.html#
APIs are here: 
https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrfxlib/mpsl/doc/api.html#mpsl-radio-notification