Boot Log

The OpenTitan boot process consists of three stages: ROM, ROM_EXT, and the first owner boot stage (e.g. BL0). Both the ROM_EXT and BL0 stages have two slots, A and B, to ensure reliable updates. This means that the actual ROM_EXT and BL0 slots executed during boot are determined at runtime.

OpenTitan stores this information in the retention SRAM as a boot_log_t struct to make it accessible to later boot stages.

Field Descriptors

• digest: HMAC digest of type hmac_digest_t for data integrity.
• identifier: Boot log identifier. The value of this field must be 0x474c4f42 (ASCII: “BOLG”).
• chip_version: scm_revision field from chip_info.
• rom_ext_slot: ROM_EXT slot (A or B) used during boot.
• bl0_slot: BL0 slot (A or B) used during boot.