The OpenTitan boot process consists of three stages:
ROM_EXT, and the first owner boot stage (e.g.
BL0 stages have two slots, A and B, to ensure reliable updates.
This means that the actual
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.
digest: HMAC digest of type
hmac_digest_tfor data integrity.
identifier: Boot log identifier. The value of this field must be
ROM_EXTslot (A or B) used during boot.
BL0slot (A or B) used during boot.