Is there any actual difference between "Fast Advertising", and "Slow Advertising" - or is it just a way to easily specify two different sets of timing parameters?
The question has been asked before; eg,
https://devzone.nordicsemi.com/f/nordic-q-a/12165/fast-advertising-and-slow-advertising (documentation link broken)
But I don't see an answer to that question.
Also, how to specify indefinite advertising; ie, with no timeout?
Various threads have suggested that a timeout of zero should do it:
But I can't see anything in any documentation which actually states that this is so.
Current (15.3.0) online Documentation: https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.sdk5.v15.3.0/lib_ble_advertising.html
As far as I know it's just a convenient feature. I actually extended that to support a "super slow" advertising interval after the slow advertising times out. I don't think it is a Bluetooth spec feature…
Yes, it's just for convenience and is optional to use. Apple recommends having both in their design guidelines: https://developer.apple.com/accessories/Accessory-Design-Guidelines.pdf (section 25.3)