Radio Notification with Connection Event Length Extension

This section clarifies the functionality of the Radio Notification signal when Connection Event Length Extension is enabled in the SoftDevice.

When Connection Event Length Extension is enabled, connection events may be extended beyond their initial tradio, to accommodate the exchange of a higher number of packet pairs. This allows more idle time to be used by the radio and will consequently affect the radio notifications.

In peripheral links, the SoftDevice will impose a limit on how long the Radio Event (tradio) may be extended, thereby restricting the maximum number of packets exchanged, to accommodate the selected tndist. Figure 1 shows consecutive Radio Events with Radio Notification signal and illustrates that the limitation in extending tradio may be required to guarantee that tndist is preserved.

Figure 1. Example: Extending the peripheral connection event is limited by the Radio Notification

In central links, Radio Notification does not impose limits on how long the Radio event (tradio) may be extended. This implies that all idle time in between connection events can be used for event extension. Because of this, the ACTIVE signal and nACTIVE signals between connection events cannot be guaranteed when Connection Event Length Extension is enabled. Figure 2 shows the idle time can be used by the central links when Connection Event Length Extension is enabled.

When a central and a peripheral link are running concurrently, the central connection event may be extended to utilize the available time until the start of the peripheral connection event. In case the central event ends too close to the start of the peripheral event, the notification signal before the peripheral connection event may not be available to the application. Figure 1 shows an example where the time distance between the central and the peripheral events is too small to allow the SoftDevice to trigger the ACTIVE notification signal.