SPRUIU1C July 2020 – February 2024 DRA821U , DRA821U-Q1
J7VCL ROM supports a combined boot image boot flow. In this flow, a boot binary blob has both Secondary bootloader (SBL) and System Firmware (SYS-FW) embedded in the boot image with a single X509 certificate. This method helps with the following situations:
To support this combined boot format, ROM employs a new X509 extension called: ext_boot_info. It supports multiple boot components with a single certificate. It allows up to 5 components as part of this extension:
This extended boot info extension replaces boot_seq (boot_info) and image_integrity extensions from the previous sections, and these should be exclusive in any given certificate.
ROM supports other extensions, such as sw_rev and debug_info, in both formats.
ROM selects the combined image flow based on the presence of ext_boot_info extension in the certificate and skips boot_seq (boot_info) and image_integrity extensions boot flow.
Having one component in ext_boot_info is same as legacy flow (that is, flow using boot_seq and image_integrity); for two or more components, ROM starts both SBL and SYS-SW, the third and fourth components are loaded by ROM to the allowed loading memory range of SBL and SYS-FW if there is no overlap in load address with executable binary info.
Each of the components can independently specify hash value of the binary, and ROM validates the hash on HS and GP if RSA degenerate key is used for signing.
Additionally, ROM rejects the full image if hash of any single component mismatches.