This document describes the ROM controller (rom_ctrl).
This module attaches as a peripheral to the system bus, and thus follows the Comportability Specification.
The ROM controller interfaces between the system bus and the ROM. This ROM has scrambled contents (scrambled with a fixed key, derived from a global constant). The controller is responsible for descrambling these contents on memory fetches.
Unlike the SRAM controller, which performs the equivalent task for SRAM, the ROM controller also contains a ROM checker block. This ROM checker is used to compute a cryptographic hash of the ROM contents just after boot, detecting any malicious changes that have been made to the ROM when the system was at rest.
- Logic for memory and address descrambling
- Post-boot ROM integrity check
- Alert trigger and status CSRs for ROM integrity errors or FSM glitches.