NimBLE-based host APIs
Apache MyNewt NimBLE is a highly configurable and BT SIG qualifiable BLE stack providing both host and controller functionalities. ESP-IDF supports NimBLE host stack which is specifically ported for ESP32 platform and FreeRTOS. The underlying controller is still the same (as in case of Bluedroid) providing VHCI interface. Refer to NimBLE user guide for a complete list of features and additional information on NimBLE stack. Most features of NimBLE including BLE Mesh are supported by ESP-IDF. The porting layer is kept cleaner by maintaining all the existing APIs of NimBLE along with a single ESP-NimBLE API for initialization, making it simpler for the application developers.
Currently, NimBLE host and controller support different transports such as UART and RAM between them. However, RAM transport cannot be used as is in case of ESP as ESP controller supports VHCI interface and buffering schemes used by NimBLE host is incompatible with that used by ESP controller. Therefore, a new transport between NimBLE host and ESP controller has been added. This is depicted in the figure below. This layer is responsible for maintaining pool of transport buffers and formatting buffers exchanges between host and controller as per the requirements.
The NimBLE host can run inside the application thread or can have its own independent thread. This flexibility is inherently provided by NimBLE design. By default, a thread is spawned by the porting function
nimble_port_freertos_init. This behavior can be changed by overriding the same function. For BLE Mesh, additional thread (advertising thread) is used which keeps on feeding advertisement events to the main thread.
To begin with, make sure that the NimBLE stack is enabled from menuconfig choose NimBLE for the Bluetooth host.
- Typical programming sequence with NimBLE stack consists of the following steps:
Initialize NVS flash using
nvs_flash_init()API. This is because ESP controller uses NVS during initialization.
Initialize the host and controller stack using
Initialize the required NimBLE host configuration parameters and callbacks
Perform application specific tasks/initialization
Run the thread for host stack using
This documentation does not cover NimBLE APIs. Refer to NimBLE tutorial for more details on the programming sequence/NimBLE APIs for different scenarios.
Initialize VHCI transport layer between NimBLE Host and ESP Bluetooth controller.
This function initializes the transport buffers to be exchanged between NimBLE host and ESP controller. It also registers required host callbacks with the controller.
ESP_OK if the initialization is successful
Appropriate error code from esp_err_t in case of an error
Deinitialize VHCI transport layer between NimBLE Host and ESP Bluetooth controller.
This function should be called after the NimBLE host is deinitialized.
ESP_OK if the deinitialization is successful
Appropriate error codes from esp_err_t in case of an error