SoftDevice Interrupt Timing

RE: SoftDevice Interrupt Timing

abkirchhoff — Wed, 20 Feb 2019 16:11:52 GMT

Simon,

Understood. I am working on how to recover if my high-priority ISR does not run when it should. Hopefully staying outside the radio prepare window should suffice 98% of the time. The Radio Notification specification lines up well with what I measured.

Thanks for your help,

Austin

RE: SoftDevice Interrupt Timing

Simonr — Wed, 20 Feb 2019 14:30:21 GMT

Hi Austin

Yes, prepare ISR of course. Putting your ISR outside of the range stated in the spec should work, but this won't be a 100% failsafe solution either. I would increase the margin with as much time I could spare. This will probably be the safest approach of accomplishing this, but I would be thorough with testing it before sticking to it.

Best regards,

Simon

RE: SoftDevice Interrupt Timing

abkirchhoff — Wed, 20 Feb 2019 13:43:26 GMT

Simon,

Thanks for your reply. I assume you meant the radio prepare ISR, as the radio start ISR seems to be very consistently about 140 us before radio reception starts (as signaled by the LNA being enabled). I guessed that the radio prepare ISR could not be guaranteed to not come at a particular time, but I thought I would ask if there were additional details or bounds.

I did find more information in the Radio Nofication section of the SoftDevice spec (S132 v3.1). The numbers in this specification give a range for when the radio prepare ISR could occur (t_prep ranges from 167 us to 1542 us). I think my app ISR should be safe most of the time if it is outside of this range by some margin. For instance, 2.5 ms before the connection event starts. Your thoughts on this approach?

Austin

RE: SoftDevice Interrupt Timing

Simonr — Wed, 20 Feb 2019 13:26:48 GMT

Hi Austin

This won't be a reliable way to go about this. The timing of the radio start ISR is not expected to stay consistent within the connection interval. Sadly I don't think there is a reliable way to accomplish what you are trying to do.

Best regards,

Simon