The firmware update process has been modelled as an event-driven state machine, with each event signifying a specific DFU procedure. The events and procedures are agnostic of the transport protocol that is in use. Therefore, it is possible to perform a firmware update using any transport protocol. The DFU controller can trigger the events by sending a corresponding message on the DFU transport.
The following figure illustrates the transitions in the state machine:
The entry point of the state machine is the bootloader starting up and entering DFU mode. During initialization, the selected transport layer is initialized. When an update process has been initiated, the DFU prepares the non-volatile memory region for the new application.
The following messages initiate transitions:
| Message type | Description |
|---|---|
| dfu_init | Initialize the Device Firmware Update module. |
| dfu_image_size_set | Set the DFU image size. |
| dfu_init_pkt_handle | Receive the init packet to be used for safety-checking as descibed in Safety-checking the image. |
| dfu_init_pkt_complete | The complete init packet has been received; execute the safety check for the first step of the DFU process. |
| dfu_data_pkt_handle | Receive a portion of the new application. |
| dfu_image_validate | Trigger validation of the new application. |
| dfu_image_activate | Activate the transferred image after validation has successfully completed. |
| dfu_sys_reset | Reset the device. A reset can occur at any time, for example if a bootloader time-out occurs or when triggered by an external message. |