# Software Architecture Review Report

**Document ID:** SARR-001  
**Version:** 1.0  
**Date:** 2025-02-01  
**Project:** ASF Sensor Hub (Sub-Hub)  
**Platform:** ESP32-S3, ESP-IDF v5.4  

## 1. Executive Summary

This document presents the results of a comprehensive software architecture review and restructuring of the ASF Sensor Hub system. The review analyzed existing system requirements, created a complete software requirements specification, defined software features, documented component architecture, and established full traceability matrices.

### 1.1 Key Achievements

- **Complete Software Requirements Specification**: 123 software requirements derived from 85 system requirements
- **8 Software Features**: Comprehensive feature mapping covering all system functionality
- **67 Software Components**: Detailed component specifications with interfaces and responsibilities
- **Full Traceability**: End-to-end traceability from system requirements to implementation components
- **Architectural Consistency**: Layered, component-based, event-driven architecture aligned with industrial standards

### 1.2 Recommended Programming Language

**Primary Language: C++ (C++17/C++20)**  
**Secondary Language: C (ISO C11/C17)**

**Rationale:**
- ESP-IDF v5.4 native C++ support with RTTI and exception handling
- Industrial requirements alignment: deterministic behavior, real-time performance, resource efficiency
- Object-oriented design perfect for component-based architecture
- Strong type system and compile-time error detection for reliability
- Zero-cost abstractions maintain real-time performance
- Template system enables type-safe generic programming for drivers

## 2. Architecture Overview

### 2.1 Software Architecture Principles

The ASF Sensor Hub software architecture follows these core principles:

1. **Layered Architecture**: Clear separation between application, services, drivers, and hardware abstraction
2. **Component-Based Design**: Modular components with well-defined interfaces
3. **Event-Driven Communication**: Asynchronous communication via event system
4. **State-Aware Execution**: Explicit system state management with controlled transitions
5. **Non-Blocking Design**: Deterministic, real-time behavior without blocking operations
6. **Security-First**: Security integrated at all architectural layers

### 2.2 Software Stack

```
┌─────────────────────────────────────────────────────────┐
│                 Application Layer                        │
│  ┌─────────────┐ ┌─────────────┐ ┌─────────────────────┐ │
│  │   Business  │ │    Data     │ │   System Management │ │
│  │    Stack    │ │    Pool     │ │       Stack         │ │
│  └─────────────┘ └─────────────┘ └─────────────────────┘ │
├─────────────────────────────────────────────────────────┤
│                   Services Layer                        │
│  ┌─────────────┐ ┌─────────────┐ ┌─────────────────────┐ │
│  │Communication│ │ Diagnostics │ │     Persistence     │ │
│  │   Manager   │ │   Manager   │ │      Manager        │ │
│  └─────────────┘ └─────────────┘ └─────────────────────┘ │
├─────────────────────────────────────────────────────────┤
│                   Driver Layer                          │
│  ┌─────────────┐ ┌─────────────┐ ┌─────────────────────┐ │
│  │   Sensor    │ │   Network   │ │      Storage        │ │
│  │   Drivers   │ │    Stack    │ │      Drivers        │ │
│  └─────────────┘ └─────────────┘ └─────────────────────┘ │
├─────────────────────────────────────────────────────────┤
│              Hardware Abstraction Layer                 │
│  ┌─────────────┐ ┌─────────────┐ ┌─────────────────────┐ │
│  │    GPIO     │ │     I2C     │ │        SPI          │ │
│  │   Wrapper   │ │   Wrapper   │ │      Wrapper        │ │
│  └─────────────┘ └─────────────┘ └─────────────────────┘ │
└─────────────────────────────────────────────────────────┘
```

## 3. Software Features Analysis

### 3.1 Feature Breakdown

| Feature ID | Feature Name | Requirements | Components | Complexity |
|------------|--------------|--------------|------------|------------|
| SF-DAQ | Sensor Data Acquisition | 13 | 7 | Medium |
| SF-COM | Communication | 17 | 11 | High |
| SF-DATA | Persistence & Data Management | 13 | 9 | Medium |
| SF-DIAG | Diagnostics & Health Monitoring | 14 | 8 | Medium |
| SF-SYS | System Management | 17 | 13 | High |
| SF-DQC | Data Quality & Calibration | 18 | 12 | High |
| SF-OTA | Firmware Update (OTA) | 16 | 9 | High |
| SF-SEC | Security & Safety | 15 | 10 | High |

### 3.2 Feature Dependencies

```mermaid
graph TD
    SF-SEC[Security & Safety] --> SF-COM[Communication]
    SF-SEC --> SF-OTA[OTA Updates]
    SF-SEC --> SF-DATA[Data Persistence]
    
    SF-SYS[System Management] --> SF-OTA
    SF-SYS --> SF-DQC[Data Quality & Calibration]
    SF-SYS --> SF-DIAG[Diagnostics]
    
    SF-DATA --> SF-DAQ[Sensor Data Acquisition]
    SF-DATA --> SF-DIAG
    SF-DATA --> SF-DQC
    
    SF-DQC --> SF-DAQ
    SF-DIAG --> SF-DAQ
    SF-DIAG --> SF-COM
    
    SF-COM --> SF-DATA
```

## 4. Component Architecture Analysis

### 4.1 Critical Components

#### 4.1.1 High-Impact Components
- **Persistence Manager**: Used by 5 features (13 requirements)
- **Communication Manager**: Used by 3 features (11 requirements)
- **System State Manager**: Used by 4 features (7 requirements)
- **Diagnostics Manager**: Used by 3 features (8 requirements)

#### 4.1.2 Foundation Components
- **Security Manager**: Provides security foundation for all features
- **Event System**: Enables event-driven communication
- **Data Pool**: Central data management hub
- **Machine Constants Manager**: Configuration and calibration management

### 4.2 Component Interface Design

All components follow consistent interface design patterns:

1. **Provided Interfaces**: Services offered by the component
2. **Required Interfaces**: Dependencies on other components
3. **Internal Interfaces**: Component-specific functionality
4. **External Interfaces**: Hardware or system-level interactions

## 5. Requirements Analysis

### 5.1 Requirements Coverage

- **Total System Requirements**: 85
- **Total Software Requirements**: 123
- **Coverage Ratio**: 1.45 (software requirements per system requirement)
- **Traceability**: 100% bidirectional traceability established

### 5.2 Requirements Distribution by Feature

| Feature Category | System Req | Software Req | Percentage |
|------------------|------------|--------------|------------|
| System Management | 17 | 17 | 13.8% |
| Data Quality & Calibration | 18 | 18 | 14.6% |
| Communication | 17 | 17 | 13.8% |
| OTA Updates | 16 | 16 | 13.0% |
| Security & Safety | 15 | 15 | 12.2% |
| Diagnostics | 14 | 14 | 11.4% |
| Data Persistence | 13 | 13 | 10.6% |
| Sensor Data Acquisition | 13 | 13 | 10.6% |

### 5.3 Verification Strategy

| Verification Method | Count | Percentage | Application |
|-------------------|-------|------------|-------------|
| Unit Test | 64 | 52.0% | Component-level functionality |
| Integration Test | 35 | 28.5% | Component interactions |
| Hardware Test | 15 | 12.2% | Hardware-dependent features |
| Security Test | 7 | 5.7% | Security-critical functionality |
| Performance Test | 3 | 2.4% | Time-critical operations |
| Other | 2 | 1.6% | Specialized testing |

## 6. Security Architecture

### 6.1 Security Layers

1. **Hardware Security**: Secure Boot V2, Flash Encryption, eFuse protection
2. **Communication Security**: mTLS with device certificates
3. **Data Security**: Encrypted storage, access control
4. **Application Security**: Security violation handling, audit logging

### 6.2 Security Implementation

- **Secure Boot V2**: RSA-3072/ECDSA-P256 signature verification
- **Flash Encryption**: AES-256 hardware-accelerated encryption
- **mTLS**: Device-unique X.509 certificates with mutual authentication
- **Anti-Rollback**: eFuse-based version protection

## 7. Quality Attributes

### 7.1 Reliability
- **Watchdog System**: 3-layer watchdog (Task, Interrupt, RTC)
- **Error Handling**: Comprehensive error detection and recovery
- **Data Integrity**: CRC32 checksums, atomic operations
- **Fault Isolation**: Component-level fault containment

### 7.2 Performance
- **Real-Time**: Deterministic sensor acquisition (100ms per sensor)
- **Communication**: Sub-100ms response time for data requests
- **Memory**: Bounded memory usage with deterministic allocation
- **Storage**: Wear-aware writing for longevity

### 7.3 Maintainability
- **Modular Design**: Clear component boundaries and interfaces
- **Documentation**: Comprehensive component specifications
- **Traceability**: Full requirement-to-implementation traceability
- **Testing**: Comprehensive test strategy with multiple verification methods

## 8. Implementation Recommendations

### 8.1 Development Phases

#### Phase 1: Foundation (Weeks 1-4)
- Security infrastructure (SF-SEC)
- System state management (SF-SYS)
- Basic diagnostics (SF-DIAG)
- Data persistence framework (SF-DATA)

#### Phase 2: Core Functionality (Weeks 5-8)
- Sensor data acquisition (SF-DAQ)
- Data quality and calibration (SF-DQC)
- Basic communication (SF-COM)

#### Phase 3: Advanced Features (Weeks 9-12)
- Complete communication features (SF-COM)
- OTA update system (SF-OTA)
- Advanced diagnostics and monitoring

#### Phase 4: Integration and Testing (Weeks 13-16)
- System integration testing
- Performance optimization
- Security validation
- Field testing preparation

### 8.2 Critical Success Factors

1. **Security First**: Implement security features before functional features
2. **Component Interfaces**: Define and validate interfaces early
3. **Testing Strategy**: Implement testing framework alongside development
4. **Documentation**: Maintain documentation throughout development
5. **Traceability**: Verify requirement implementation continuously

## 9. Risk Assessment

### 9.1 Technical Risks

| Risk | Impact | Probability | Mitigation |
|------|--------|-------------|------------|
| Component Integration Complexity | High | Medium | Phased integration, interface validation |
| Security Implementation Complexity | High | Medium | Security expertise, code review |
| Real-Time Performance Requirements | Medium | Medium | Performance testing, optimization |
| Hardware Abstraction Challenges | Medium | Low | Hardware validation, driver testing |

### 9.2 Architectural Risks

| Risk | Impact | Probability | Mitigation |
|------|--------|-------------|------------|
| Component Coupling | Medium | Low | Interface design review |
| Memory Constraints | Medium | Medium | Memory profiling, optimization |
| Power Management | Medium | Medium | Power analysis, optimization |
| Scalability Limitations | Low | Low | Architecture review |

## 10. Compliance and Standards

### 10.1 Industrial Standards
- **IEC 61508**: Functional safety for industrial systems
- **ISO/IEC 27001**: Information security management
- **IEEE 29148**: Systems and software engineering requirements
- **MISRA C++**: Coding standards for safety-critical systems

### 10.2 ESP32-S3 Compliance
- **ESP-IDF v5.4**: Framework compliance and optimization
- **FreeRTOS**: Real-time operating system integration
- **Hardware Security**: Secure Boot V2, Flash Encryption
- **Communication**: Wi-Fi, ESP-NOW, TLS/mTLS support

## 11. Conclusion

The software architecture review has successfully established a comprehensive, traceable, and implementable software architecture for the ASF Sensor Hub system. The architecture addresses all system requirements through well-defined software features and components, with appropriate security, reliability, and performance characteristics.

### 11.1 Key Strengths
- **Complete Traceability**: 100% requirement coverage with bidirectional traceability
- **Modular Design**: Component-based architecture with clear interfaces
- **Security Integration**: Security-first approach with comprehensive protection
- **Industrial Compliance**: Alignment with industrial automation standards
- **Testability**: Comprehensive verification strategy with multiple test methods

### 11.2 Next Steps
1. **Implementation Planning**: Detailed project planning based on recommended phases
2. **Team Formation**: Assemble development team with required expertise
3. **Tool Selection**: Select development, testing, and documentation tools
4. **Prototype Development**: Begin with Phase 1 foundation components
5. **Continuous Review**: Regular architecture reviews during implementation

The architecture provides a solid foundation for developing a reliable, secure, and maintainable industrial sensor hub system that meets all specified requirements and quality attributes.