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 t_radio 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 (t_radio) may be extended, thereby restricting the maximum number of packets exchanged to accommodate the selected t_ndist. The following figure shows an example where the Radio Notification t_ndist is limiting the extension of the first Radio Event.

In central links, Radio Notification does not impose limits on how long the Radio event (t_radio) 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. The following figure shows an example of how the idle time between connection events can be utilized when Connection Event Length Extension and Radio Notification signals are 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. Radio Event distance too short to trigger the notification signal shows an example where the time distance between the central and the peripheral events is too short to allow the SoftDevice to trigger the ACTIVE notification signal.