How close can timeslots be scheduled?

[Bjorn191023]

Hi,

I want to schedule timeslots back-to-back, or as close as possible. Question is how close to eachother timeslots can be scheduled?

I read the following about sd_radio_request() at https://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.s140.api.v7.2.0%2Fgroup___n_r_f___s_o_c___f_u_n_c_t_i_o_n_s.html&anchor=ga3fbd3ade121c15745cc19b900ce8154b:

"A too small p_request->distance_us will lead to a NRF_EVT_RADIO_BLOCKED event."
1) What is the minimum distance?

"Timeslots scheduled too close will lead to a NRF_EVT_RADIO_BLOCKED event."
2) What is "too close" meaning what is the required minimum time from calling sd_radio_request() until the timeslot is due?
3) What is the required minimum time from returning NRF_RADIO_SIGNAL_CALLBACK_ACTION_REQUEST_AND_END from the signal handler until the timeslot is due? Same as question 2 above?

I have done some measurements, where I request a new timeslot from the signal handler as close as possible to the current:

With NRF_RADIO_HFCLK_CFG_NO_GUARANTEE:
175 us until next timeslot is due => WORKS
165 us until next timeslot is due => DOESNT WORK

With NRF_RADIO_HFCLK_CFG_XTAL_GUARANTEED:
295 us until next timeslot is due => WORKS
285 us until next timeslot is due => DOESNT WORK

So my measurements suggest the response to question 3 above is:
a) 170 us with NRF_RADIO_HFCLK_CFG_NO_GUARANTEE
b) 290 us with NRF_RADIO_HFCLK_CFG_XTAL_GUARANTEED

This is longer than I would expect.

Please provide official specifications!

I'm running on a nRF52840 DK.

SDK ver 16.0.0

S140_nrf52_7.0.1

BR / Björn

[Simonr]

Hi again Björn

I discussed this with one of our "timeslot experts", and in order to get the next timeslot event as close as possible to the last one, we suggest using the nrf_radio_request_earliest call to get the next timeslot as early as possible. Unfortunately, it doesn't seem like we have any definition on how short this is, and we can't guarantee any shorter intervals than what you are already seeing for NRF_RADIO_HFCLK_CFG_NO_GUARANTEE or NRF_RADIO_HFCLK_CFG_XTAL_GUARANTEED.

Our expert also suggest using a combination of this "earliest" call between timeslots and extending them for the best behavior. I don't see why the separately requested timeslots would "give TX its own timeslot sub-sequent events", as I think the SoftDevice won't stop in the middle of an extended timeslot to get the radio back once requested either way.

Best regards,

Simon

[Bjorn191023]

Hi Simon,

Sorry, we cant use earliest since we need exact timing on micro-sec level between BIS-events. So normal is required.

I understand your response so that it's not possible to schedule separate timeslots with 150 us between. Thanks, then I know, even if I was hoping for another answer ;-)

BR / Björn