There are two DFU package formats:
- Legacy - Uses a simple structure and has no security.
- Modern - Uses Google's protocol buffers for serialization and can be cryptographically signed.
The transition from legacy to modern DFU package format occurred in the nRF5 SDK v12.0.0. nRF Util for nRF5 SDK supports only modern firmware packages compatible with nRF5 SDK v15.3.0 and later. For support of earlier SDKs and the legacy firmware format, refer to the documentation for the legacy Python package: nRF Util User Guide v6.1.0.
Note
By default, firmware images compatible with nRF SDK 15.3.0 and later are created. Firmware images compatible with nRF SDK 12.0 to nRF SDK 15.0 can be supported by using the --no-backup command when generating the DFU settings.