Using timeslot API and fds

[Bert Thomas]

Hi all,

I am working on a project that requires simultaneous usage of BLE and ESB. I implemented that with the timeslot API and it basically works. However, I need to store some data to flash using fds when a certain packet is received using ESB. I am experiencing a lot of problems to get this to work properly, most notably fds functions returning errors (1, FDS_ERR_OPERATION_TIMEOUT). it seems to make sense to me that the softdevice APIs can't be used during a timeslot. I suppose I must postpone the write action until the softdevice is active again, that is: the timeslot has ended. But what event can I use to be sure the softdevice is ready to be used again, so that I can handle my fds stuff there?

Regards,

Bert

[bjorn-spockeli]

Hi Bart, 

it should be safe to call the sd_-API after you have received the NRF_EVT_RADIO_SESSION_CLOSED event, which indicates that the timeslot has been closed and the SoftDevice is in control of the peripherals it uses.

Best regards

Bjørn

[Bert Thomas]

Thanks for your reply!

At startup I invoke sd_radio_session_open(). Each time the timeslot has elapsed the timer0 handler returns NRF_RADIO_SIGNAL_CALLBACK_ACTION_REQUEST_AND_END to schedule the next timeslot. At what moment am I supposed to receive RADIO_SESSION_CLOSED event? Shouldn't I invoke sd_radio_session_close() to accomplish this? But I assume that to be able to execute sd_radio_session_close() the timeslot must have ended, right?  So I'm confused...

[bjorn-spockeli]

Ah, sorry Bert you are correct. 

You should use the NRF_RADIO_CALLBACK_SIGNAL_TYPE_TIMER0 event, which should be generated about 100uS or so before the timeslot ends. So you either call sd_radio_session_close() here and then use the NRF_EVT_RADIO_SESSION_CLOSED event to trigger the Flash operations  or you can start an application timer here to timeout after about 100us and use its timeout handler to initiate the flash operations. 

It should be fine to call sd_radio_session_close while the timeslot is open, see https://devzone.nordicsemi.com/nordic/short-range-guides/b/software-development-kit/posts/setting-up-the-timeslot-api

[Bert Thomas]

When I execute sd_radio_session_close() the softdevice code runs into the hardfault handler. Are you sure I can execute sd_radio_session_close() from the timer0 handler?

[bjorn-spockeli]

Hi Bert, 

It the Timer 0 Interrupt handler has a higher priority than 4, then calling the sd_- API will result in a HardFault, see Interrupt priority levels.  

The priorities of the interrupts reserved by the SoftDevice cannot be changed. 
This includes the SVC interrupt. Handlers running at a priority level higher
than 4 (lower numerical priority value) have neither access to SoftDevice functions 
nor to application specific SVCs or RTOS functions running at lower priority levels
(higher numerical priority values).

So if the Timer0 handler has a higher priority than 4 you need to schedule the sd_radio_session_close() call to be called from a lower priority or  from main's context. 

Best regards

Bjørn

[Bert Thomas]

Yes, this solved it! It's working now as expected. Thanks!

[bjorn-spockeli]

Happy to help!