Firmware Update Server

The Firmware Update Server model implements the Target node functionality of the Device Firmware Update (DFU) subsystem. It extends the BLOB Transfer Server, which it uses to receive the firmware image binary from the Distributor node.

Together with the extended BLOB Transfer Server model, the Firmware Update Server model implements all the required functionality for receiving firmware updates over the mesh network, but does not provide any functionality for storing, applying or verifying the images.

Firmware images

The Firmware Update Server holds a list of all the updatable firmware images on the device. The full list shall be passed to the server through the _imgs parameter in BT_MESH_DFU_SRV_INIT, and must be populated before the Bluetooth mesh subsystem is started. Each firmware image in the image list must be independently updatable, and should have its own firmware ID.

For instance, a device with an upgradable bootloader, an application and a peripheral chip with firmware update capabilities could have three entries in the firmware image list, each with their own separate firmware ID.

Receiving transfers

The Firmware Update Server model uses a BLOB Transfer Server model on the same element to transfer the binary image. The interaction between the Firmware Update Server, BLOB Transfer Server and application is described below:

Bluetooth mesh Firmware Update Server transfer

Transfer check

The transfer check is an optional pre-transfer check the application can perform on incoming firmware image metadata. The Firmware Update Server performs the transfer check by calling the check callback.

The result of the transfer check is a pass/fail status return and the expected bt_mesh_dfu_effect. The DFU effect return parameter will be communicated back to the Distributor, and should indicate what effect the firmware update will have on the mesh state of the device. If the transfer will cause the device to change its Composition Data or become unprovisioned, this should be communicated through the effect parameter of the metadata check.

Start

The Start procedure prepares the application for the incoming transfer. It’ll contain information about which image is being updated, as well as the update metadata.

The Firmware Update Server start callback must return a pointer to the BLOB Writer the BLOB Transfer Server will send the BLOB to.

BLOB transfer

After the setup stage, the Firmware Update Server prepares the BLOB Transfer Server for the incoming transfer. The entire firmware image is transferred to the BLOB Transfer Server, which passes the image to its assigned BLOB Writer.

At the end of the BLOB transfer, the Firmware Update Server calls its end callback.

Image verification

After the BLOB transfer has finished, the application should verify the image in any way it can to ensure that it is ready for being applied. Once the image has been verified, the application calls bt_mesh_dfu_srv_verified().

If the image can’t be verified, the application calls bt_mesh_dfu_srv_rejected().

Applying the image

Finally, if the image was verified, the Distributor may instruct the Firmware Update Server to apply the transfer. This is communicated to the application through the apply callback. The application should swap the image and start running with the new firmware. The firmware image table should be updated to reflect the new firmware ID of the updated image.

When the transfer applies to the mesh application itself, the device might have to reboot as part of the swap. This restart can be performed from inside the apply callback, or done asynchronously. After booting up with the new firmware, the firmware image table should be updated before the Bluetooth mesh subsystem is started.

The Distributor will read out the firmware image table to confirm that the transfer was successfully applied. If the metadata check indicated that the device would become unprovisioned, the Target node is not required to respond to this check.

API reference

group bt_mesh_dfu_srv

API for the Bluetooth mesh Firmware Update Server model.

Defines

BT_MESH_DFU_SRV_INIT(_handlers, _imgs, _img_count)

Initialization parameters for Firmware Update Server model.

Parameters:

_handlers – DFU handler function structure.
_imgs – List of bt_mesh_dfu_img managed by this Server.
_img_count – Number of DFU images managed by this Server.

BT_MESH_MODEL_DFU_SRV(_srv)

Firmware Update Server model entry.

Parameters:

_srv – Pointer to a Firmware Update Server model instance.

Functions

void bt_mesh_dfu_srv_verified(struct bt_mesh_dfu_srv *srv)

Accept the received DFU transfer.

Should be called at the end of a successful DFU transfer.

If the DFU transfer completes successfully, the application should verify the image validity (including any image authentication or integrity checks), and call this function if the image is ready to be applied.

Parameters:

srv – Firmware Update Server instance.

void bt_mesh_dfu_srv_rejected(struct bt_mesh_dfu_srv *srv)

Reject the received DFU transfer.

Should be called at the end of a successful DFU transfer.

If the DFU transfer completes successfully, the application should verify the image validity (including any image authentication or integrity checks), and call this function if one of the checks fail.

Parameters:

srv – Firmware Update Server instance.

void bt_mesh_dfu_srv_cancel(struct bt_mesh_dfu_srv *srv)

Cancel the ongoing DFU transfer.

Parameters:

srv – Firmware Update Server instance.

void bt_mesh_dfu_srv_applied(struct bt_mesh_dfu_srv *srv)

Confirm that the received DFU transfer was applied.

Should be called as a result of the bt_mesh_dfu_srv_cb::apply callback.

Parameters:

srv – Firmware Update Server instance.

bool bt_mesh_dfu_srv_is_busy(const struct bt_mesh_dfu_srv *srv)

Check if the Firmware Update Server is busy processing a transfer.

Parameters:

srv – Firmware Update Server instance.

Returns:

true if a DFU procedure is in progress, false otherwise.

uint8_t bt_mesh_dfu_srv_progress(const struct bt_mesh_dfu_srv *srv)

Get the progress of the current DFU procedure, in percent.

Parameters:

srv – Firmware Update Server instance.

Returns:

The current transfer progress in percent.

struct bt_mesh_dfu_srv_cb

#include <dfu_srv.h>

Firmware Update Server event callbacks.

Public Members

int (*check)(struct bt_mesh_dfu_srv *srv, const struct bt_mesh_dfu_img *img, struct net_buf_simple *metadata, enum bt_mesh_dfu_effect *effect)

Transfer check callback.

The transfer check can be used to validate the incoming transfer before it starts. The contents of the metadata is implementation specific, and should contain all the information the application needs to determine whether this image should be accepted, and what the effect of the transfer would be.

If applying the image will have an effect on the provisioning state of the mesh stack, this can be communicated through the effect return parameter.

The metadata check can be performed both as part of starting a new transfer and as a separate procedure.

This handler is optional.

Param srv:: Firmware Update Server instance.
Param img:: DFU image the metadata check is performed on.
Param metadata:: Image metadata.
Param effect:: Return parameter for the image effect on the provisioning state of the mesh stack.
Return:: 0 on success, or (negative) error code otherwise.

int (*start)(struct bt_mesh_dfu_srv *srv, const struct bt_mesh_dfu_img *img, struct net_buf_simple *metadata, const struct bt_mesh_blob_io **io)

Transfer start callback.

Called when the Firmware Update Server is ready to start a new DFU transfer. The application must provide an initialized BLOB stream to be used during the DFU transfer.

The following error codes are treated specially, and should be used to communicate these issues:

-ENOMEM: The device cannot fit this image.
-EBUSY: The application is temporarily unable to accept the transfer.
-EALREADY: The device has already received and verified this image, and there’s no need to transfer it again. The Firmware Update model will skip the transfer phase, and mark the image as verified.

This handler is mandatory.

Param srv:: Firmware Update Server instance.
Param img:: DFU image being updated.
Param metadata:: Image metadata.
Param io:: BLOB stream return parameter. Must be set to a valid BLOB stream by the callback.
Return:: 0 on success, or (negative) error code otherwise. Return codes -ENOMEM, -EBUSY -EALREADY will be passed to the updater, other error codes are reported as internal errors.

void (*end)(struct bt_mesh_dfu_srv *srv, const struct bt_mesh_dfu_img *img, bool success)

Transfer end callback.

This handler is optional.

If the transfer is successful, the application should verify the firmware image, and call either bt_mesh_dfu_srv_verified or bt_mesh_dfu_srv_rejected depending on the outcome.

If the transfer fails, the Firmware Update Server will be available for new transfers immediately after this function returns.

Param srv:: Firmware Update Server instance.
Param img:: DFU image that failed the update.
Param success:: Whether the DFU transfer was successful.

int (*recover)(struct bt_mesh_dfu_srv *srv, const struct bt_mesh_dfu_img *img, const struct bt_mesh_blob_io **io)

Transfer recovery callback.

If the device reboots in the middle of a transfer, the Firmware Update Server calls this function when the Bluetooth mesh subsystem is started.

This callback is optional, but transfers will not be recovered after a reboot without it.

Param srv:: Firmware Update Server instance.
Param img:: DFU image being updated.
Param io:: BLOB stream return parameter. Must be set to a valid BLOB stream by the callback.
Return:: 0 on success, or (negative) error code to abandon the transfer.

int (*apply)(struct bt_mesh_dfu_srv *srv, const struct bt_mesh_dfu_img *img)

Transfer apply callback.

Called after a transfer has been validated, and the updater sends an apply message to the Target nodes.

This handler is optional.

Param srv:: Firmware Update Server instance.
Param img:: DFU image that should be applied.
Return:: 0 on success, or (negative) error code otherwise.

struct bt_mesh_dfu_srv

#include <dfu_srv.h>

Firmware Update Server instance.

Should be initialized with BT_MESH_DFU_SRV_INIT.

Public Members

struct bt_mesh_blob_srv blob: Underlying BLOB Transfer Server.

const struct bt_mesh_dfu_srv_cb *cb: Callback structure.

const struct bt_mesh_dfu_img *imgs: List of updatable images.

size_t img_count: Number of updatable images.