SoftDevice timing-activities and priorities

The SoftDevice supports multiple connections simultaneously in addition to an Observer or a Scanner. In addition to these Bluetooth® Low Energy roles, Flash memory API, Quality of Service (QoS) channel survey, and Radio Timeslot API can also run simultaneously.

Central link timing-events are added relative to already running central link timing-events. Flash access timing-event and Radio Timeslot timing-event are scheduled independently and may occur at the same time and collide. QoS channel survey timing-events are scheduled the same way as the scanner, which means relative to existing central link timing-events, but the QoS channel survey timing-events always have the lowest priority. If central links, scanner, and the QoS channel survey are scheduled with a common base interval and the sum of their timing-event lengths is less than this interval, they never block each other. If a channel survey timing-event is blocked by a higher priority event, the timing-event is skipped and a new one is requested one interval later.

The different timing-activities have different priorities at different times, dependent upon their state. As an example, if a connection is about to reach supervision time-out, it will block all other timing-activities and get the timing-event it requests. In this case, all other timing-activities will be blocked if they overlap with the connection timing-event, and they will have to be rescheduled. The following table summarizes the priorities.