What is the radio time slice schedule between scanning and advertisement for central device when both are enabled?

[inderveer]

Hi,

I am using NRF52833 with soft device version s140. I have set the advertisement duration for the BLE app to 0 (meaning the duration is infinite). Also, I have set scanning timeout 0 (this also means the timeout is infinite). But the device cannot scan and advertisement at same time literally, there will be some time slicing to manage both these processes such that one process is executed at one time. What will be this time slicing value and how can I get this value?

[Einar Thorsrud]

Hi,

The main factor here is selecting sensible intervals and windows to make the scheduling easier. There is no API for he SoftDevice to feedback the duty cycle of scannign or advertising and the time when neither happens, though. Note that the scheduler has a priority list.

To get an idea of the minimum time it could take you can look at the processur usage in us before and after advertising and scanning, here and here.

[inderveer]

So, there is no way to find the exact time slicing between advertising and scanning if the device has enabled both?

[Einar Thorsrud]

I would not say it is not possible, but the number is not provided anywhere and calculating it yourself is difficult (it may also vary depending on advertising random offset etc). One way to find out what is currently happening (more suitable in a lab setting than in a product) is to connect relevant Radio evens to GPIOTE and toggle pins to see when the radio is in Tx an Rx via PPI, and check with a logic analyzer (or hook it up to the EGU to generate interrupts if you want to do it in software).

[inderveer]

I have an observation with the current measurements data when both scanning, and advertisement is happening simultaneously:

1. When scanning window is going on, then the advertisement event is skipped.

2. Only after the scanning window when no other radio event is in progress, the advertisement event is allowed to be executed.

Is my analysis accurate?

[Einar Thorsrud]

Hi,

Yes, you are right. If you want to maximize the time advertising and scanning, and reduce the time time doing none you should pick parameters that make scheduling simpler and perhaps also shorter scan intervals to loose less scan time when advertising is prioritized (see this post).