Is there a way to detect or be notified when an advertisment is about to be sent?

[Tim]

Says it all in the title. I'm making a sensor which puts its data in a non-directed non-connectable advertisment packet. I want to read the sensor just before it is sent. The timing is not super-critical - within 0.1s would be fine.

I can't find anything in the softdevice API about this. Is there a way to use radio interrupts or similar?

[John]

I'm going to assume you are using the soft device stack. In which case, you can use the Radio Notification feature of the stack to be alerted each time the radio is going to become active or has gone inactive. You will have options on the amount of lead time prior to the radio becoming active so you can set it up to best meet your needs. See section 7 of the S110 SoftDevice Specification for more information on Radio Notification.

[Asbjørn]

Just wanted to add links to the documentation of the functionality mentioned by @John DeWitt.

SDK documentation of the functions.

See chapter 7 of the S110 softdevice specification.