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Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Clear out junk files and repair common Windows errorsFree Scan →Scan for outdated or missing drivers - takes under a minuteDriver Scan →Zephyr’s Bluetooth Low Energy (BLE) Controller implements the Link Layer: the real-time part of Bluetooth that schedules radio activity, sends and receives packets, and handles Link Layer control procedures. It works with a 2.4 GHz radio and can run alongside Zephyr’s Host on one chip or communicate with a separate Host through the Host Controller Interface (HCI).
What the Zephyr BLE Controller does
Bluetooth is commonly described in three layers: the application, the Host, and the Controller. The application defines what a product does; the Host provides higher-level Bluetooth protocols; and the Controller handles the Link Layer (LE LL), including time-sensitive over-the-air communication. Radio hardware supplies the functions that transmit and receive in the 2.4 GHz band. The layers are distinct even when they run together in one firmware image. Nordic’s Zephyr stack architecture documentation describes this division and the role of HCI between Host and Controller.
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Inside the implementation
Zephyr’s controller architecture includes HCI support, hardware abstraction, a Ticker scheduler, a software Link Layer, and utility components. The Ticker coordinates radio and other resource use on a soft real-time schedule. The software Link Layer manages roles and state, control procedures, and packet-controller behavior. Utilities include memory pools, queues, and Mayfly, which supports deferred interrupt execution. See the Zephyr LE Controller architecture for implementation details.
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Choose a single-chip or split-chip configuration
The right arrangement depends on whether the application and Host should share a microcontroller with the Controller, or whether a separate processor should handle the radio-facing work.
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| Configuration | What runs where | How the layers communicate | Typical consideration |
|---|---|---|---|
| Combined, single-chip | Application, Host, Controller, and radio interface run on one microcontroller. | The Host and Controller communicate internally through calls and RAM queues; the Bluetooth specification does not prescribe this internal HCI behavior. | Can suit a design seeking a small footprint and low power, subject to the selected hardware and build. |
| Dual-chip / split | Application and Host run on one IC; Controller and radio run on another. | HCI provides the standard Host/Controller interface. Zephyr documents Linux BlueZ as an example of an external Host. | Requires a suitable HCI transport and compatible Host and Controller implementations. |
These topology descriptions and the BlueZ example are documented in Nordic’s stack architecture page.
Match the Zephyr build type to the topology
Zephyr documents three broad Bluetooth build types. A combined build is usually the straightforward choice when the application and Bluetooth stack belong in one firmware image; a controller-only build is for exposing a Controller to an external Host; and a host-only build uses an external Controller.
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- Controller-only: Link Layer plus an HCI-facing application, with a selected physical transport.
- Host-only: Application and Host, with an HCI driver for an external Controller.
- Combined: Application, Host, and Controller in one image for a single-chip arrangement.
Controller-only configuration
For the controller-only configuration, Nordic’s nRF Connect SDK documentation gives typical Kconfig settings CONFIG_BT=y, CONFIG_BT_HCI=y, and CONFIG_BT_HCI_RAW=y. Controller enablement also depends on the applicable device-tree node. These are examples from the current Nordic SDK documentation, not universal settings for every upstream Zephyr release or target; check the documentation and sample for the exact version you build. Stack Architecture provides the configuration context.
Select an HCI transport for a split system
HCI defines the Host/Controller boundary, while a physical or interprocessor transport carries the messages between them. Zephyr’s Bluetooth sample catalog includes examples for HCI 3-wire (H:5), HCI IPC, HCI SPI, HCI UART, asynchronous HCI UART, and HCI USB. Choose an example that matches the available interfaces, both sides of the connection, and the selected software version; the presence of a sample does not by itself establish that every board supports that transport. See the Zephyr Bluetooth samples.
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Linux BlueZ as the Host
Yes. Zephyr documents Linux BlueZ as an example of an external Host communicating with a Zephyr Controller over HCI. That does not mean every Zephyr board or HCI transport will work automatically with every BlueZ setup: confirm that the Controller build, transport, host-side driver, and connection wiring match. The cited architecture documentation establishes the arrangement, but does not specify a single universal setup procedure.
Check hardware before choosing a Controller target
A BLE-capable radio alone is not enough to establish that a target can run a particular Zephyr Controller configuration. Nordic’s controller documentation lists hardware resources that can be required, including high- and low-frequency clocks, RTCs and timers, PPI or DPPI, software interrupts, a 2.4 GHz radio, random-number generation, cryptographic peripherals, and optional GPIO control for a power amplifier or low-noise amplifier. The exact requirements vary by SoC generation and configuration. Use the controller hardware requirements alongside the board target and release-specific support information.
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nRF5340: account for both cores
For the documented Zephyr Bluetooth sample setup on an nRF5340, an application-core Bluetooth sample is paired with the HCI IPC sample on the network core, where the LE Controller runs. Build and program the matching network-core image as well as the application-core firmware; the application-core sample is not a self-contained Bluetooth image in this arrangement. The Bluetooth sample instructions describe this pairing.
A Nordic nRF52-family development board can be a practical category for experimentation, but verify the specific board target, SoC resources, Zephyr support, and intended transport before selecting hardware. No particular board listing or price is established here.
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Build, test, and validate the intended use case
Start with a Zephyr Bluetooth sample that matches the desired build type and transport, then confirm its board target and any required companion image. For a split system, verify that the HCI transport is implemented and enabled on both sides. For a single-chip system, use the combined build unless the design specifically needs an HCI-facing Controller.
Zephyr’s controller documentation describes procedure-focused unit tests that emulate parts of receive/transmit and event-preparation flows. Those tests indicate how controller behavior is tested in software; they are not evidence that a particular board has been tested in a specific radio environment or has passed complete Bluetooth interoperability qualification. Feature availability and qualification depend on target, controller, and software version. Check the selected release’s feature and qualification documentation for the exact product requirement rather than treating a successful build as proof of certification. See the Zephyr LE Controller documentation.
Quick Recap
How to choose an arrangement
- Choose a combined build when application, Host, and Controller should run together on one microcontroller and the target supports the required Bluetooth resources.
- Choose controller-only when a separate Host needs a Zephyr Controller through HCI.
- Choose host-only when the Zephyr application and Host will use a separate Controller.
- For a split design, settle the HCI transport and host compatibility before committing to the board and wiring.
- For multicore hardware, identify which core runs the Controller and whether a companion firmware image must be built and programmed.
- Check feature support against the exact Zephyr or vendor SDK release used for the project.
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