FFI Access Firewall Segmentation for Mixed-Criticality SoCs

Solution Overview

Problem

Existing systems-on-a-chip (SoCs) face challenges in implementing freedom from interference (FFI) and memory read/write protection for mixed safety criticality levels, particularly due to limitations in MMUs, MPUs, and security firewalls, which cannot efficiently handle the complexity and number of components with varying ASIL levels, leading to increased costs and latency.

Innovation Solution

A combination of Master-side and Slave-side enhancements using MMUs, MPUs, security firewalls, and safety privilege access IDs (PrivIDs) to enforce comprehensive FFI rules, allowing software-programmable access attributes and efficient handling of multiple safety criticality levels, even for components without MMUs or MPUs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional MMUs, MPUs, and security firewalls are used to enforce FFI rules, then memory access protection is provided, but the system cannot efficiently handle the complexity and number of components with varying ASIL levels, leading to increased costs and latency

Engineering Contradiction:

ImproveFFI enforcement reliabilityVSAvoidsystem complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The system segments FFI rule enforcement into two distinct parts: (1) a firewall filter stage that performs initial access request filtering based on component identity and target address, and (2) an MMU stage that handles translation and additional access control. This segmentation allows the firewall to handle simple cases efficiently while the MMU processes only remaining cases, reducing overall system complexity and latency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces an intermediary component between the memory master and the MMU that acts as a firewall. This intermediary filters access requests before they reach the MMU, reducing the burden on the MMU and enabling more efficient handling of multiple components with varying ASIL levels. The intermediary uses PrivIDs and access attributes to enforce FFI rules without requiring full MMU processing for every request.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If traditional MMUs, MPUs, and security firewalls are used to enforce FFI rules, then memory access protection is provided, but latency increases due to the inability to efficiently handle multiple safety criticality levels

Engineering Contradiction:

ImproveFFI enforcement reliabilityVSAvoidaccess latency

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The system segments FFI rule enforcement into two distinct parts: (1) a firewall filter stage that performs initial access request filtering based on component identity and target address, and (2) an MMU stage that handles translation and additional access control. This segmentation allows the firewall to handle simple cases efficiently while the MMU processes only remaining cases, reducing overall system complexity and latency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The firewall performs partial FFI enforcement by filtering access requests based on PrivIDs and access attributes before they reach the MMU. This partial action allows the system to enforce FFI rules for many cases without requiring full MMU processing, thereby reducing latency while maintaining reliability.

Inventive Principle:

Principle #16Partial or excessive action

3Reliability

If traditional MMUs, MPUs, and security firewalls are used to enforce FFI rules, then access control is provided, but costs increase due to the complexity of handling mixed safety criticality levels

Engineering Contradiction:

ImproveFFI enforcement reliabilityVSAvoidsystem implementation cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The system segments FFI rule enforcement into two distinct parts: (1) a firewall filter stage that performs initial access request filtering based on component identity and target address, and (2) an MMU stage that handles translation and additional access control. This segmentation allows the firewall to handle simple cases efficiently while the MMU processes only remaining cases, reducing overall system complexity and latency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The firewall component is designed to be universal by handling FFI rule enforcement for multiple components with varying ASIL levels using a common PrivID and access attribute mechanism. This multi-functionality reduces the need for separate dedicated protection mechanisms for each component, thereby reducing implementation costs while maintaining reliability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS20250225233A1Method and system for freedom from interference (FFI)

Publication Date: 2025.07.10 TEXAS INSTRUMENTS INC

AI summary

Systems, devices and methods implement freedom from interference (FFI) access rules. An example system includes a first set of components; a second set of components; and an interconnect between the two sets of components. Each component of the second set executes tasks in which requests for access are generated for access to one or more components of the first set of components. Each request for access is associated with a set of rules indicating whether a component of the second set, when executing a task generating the request for access, is permitted to access a component of the first set of components to which the request for access is directed, and what type of access, of multiple types of access, is permitted to the component to which the request for access is directed.