SoftDevice

SoftDevice is Nordic Semiconductor’s term for a precompiled, binary software stack that provides the Bluetooth Low Energy (BLE) protocol implementation and related radio control for its nRF series System on Chips. It runs alongside the user application on the same microcontroller and is delivered as a dedicated binary that occupies a defined flash region and a reserved RAM area. The SoftDevice implements the BLE stack (GAP, GATT, L2CAP/ATT), security and bonding, connection management, and radio timing, with some variants also supporting other wireless protocols such as ANT.

To use the SoftDevice, developers link against the SoftDevice library and enable it at startup via the SoftDevice API. The application registers event handlers to receive BLE events from the stack and uses high-level APIs to perform advertising, scanning, connections, and security procedures. Interaction with the SoftDevice is strictly through its API; the application must not directly manipulate SoftDevice internal memory. The SoftDevice handles radio scheduling and resource management, and it exposes an event-driven model where BLE events are dispatched to the application for processing.

Different SoftDevice variants offer varying capabilities and resource footprints, such as single-role (peripheral-only) or multi-role (central and peripheral) configurations, and different maximum numbers of connections. The exact features and memory requirements depend on the specific SoC and SoftDevice version. SoftDevices are proprietary, provided by Nordic as part of the nRF5 SDK or nRF Connect SDK, and usage is subject to the vendor’s licensing terms. The SoftDevice is designed to work in concert with the application firmware, not as a standalone operating system.