Delta Firmware Over The Air (DFOTA) Update: Optimizing device updates in Zephyr

Firmware Over The Air (FOTA) updates are a well-established method for updating devices, but this approach shows its limitations in the embedded world. Indeed, in embedded systems we have 2 main constraints (among others) when discussing firmware updates : memory and bandwidth. Regarding memory, developing a low-memory-footprint API was our priority when creating this solution. To explain how we built this API, we will discuss compression algorithms and justify our choice of implementing in Zephyr the open-source library "Heatshrink" which is ideally suited for DFOTA's needs and for embedded systems in general (we can demonstrate the memory footprint differences compared to the already implemented compression algorithm "LZ4"). Next, we will see how deltas (or patches) between two firmware versions are generated (we could present a benchmark to illustrate the data savings achieved by sending patches instead of the full firmware, as it is done during FOTA update). Further, we will explore the implementation of the DFOTA API to explain how it works and how it can be implemented into your project.