Developed comprehensive secure build and run documentation for the flipperdevices/u-boot repository, focusing on integrating TF-A and OP-TEE to enable secure-state workflows. Leveraged expertise in embedded systems and QEMU to create reproducible, end-to-end instructions for building and testing U-Boot in EL3/EL2 secure states. The work included detailed reStructuredText documentation, outlining precise build steps, command usage, and QEMU invocation examples. This contribution improved onboarding and knowledge transfer for developers, reducing the time required to implement secure features. No bug fixes were addressed during this period, with efforts concentrated on enhancing security posture and workflow reproducibility through robust documentation.