# Engineering Review Report

## A. Executive Summary

### Overall System Maturity Level
The ASF Sensor Hub demonstrates a well-structured architecture with clear layering, defined responsibilities, and adherence to embedded system constraints. However, several critical gaps and risks need to be addressed before proceeding to the implementation phase.

### Major Risks (Top 5)
1. **Cross-Feature Conflicts**: Potential timing conflicts between OTA updates and DAQ operations.
2. **State Machine Completeness**: Undefined transitions for error handling and degraded states.
3. **Data Integrity Risks**: Insufficient guarantees for data persistence during power loss.
4. **Security Gaps**: Lack of detailed secure boot and cryptographic key management mechanisms.
5. **Scalability Concerns**: Limited provisions for adding new sensor types or features.

### Go / No-Go Recommendation
**No-Go**: Address the identified critical risks and gaps before proceeding to the implementation phase.

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## B. Detailed Findings

### 1. Architecture

#### Findings:
- **Layering & Separation of Concerns**: Proper abstraction boundaries are defined, but direct hardware access by features bypassing the System Manager is a risk. **Severity: Major**
- **State Machine Validity**: Some states (e.g., ERROR, DEGRADED) lack defined transitions and behaviors. **Severity: Critical**

#### Recommendations:
- Enforce strict access controls to hardware and persistence layers.
- Define and document all state transitions and behaviors.

### 2. Requirements

#### Findings:
- **Missing Requirements**: No explicit requirements for handling SD card wear or power loss scenarios. **Severity: Critical**
- **Conflicting Requirements**: OTA updates may interfere with real-time DAQ operations. **Severity: Major**

#### Recommendations:
- Add requirements for wear leveling and power loss recovery.
- Define OTA timing constraints to avoid conflicts.

### 3. Performance

#### Findings:
- **Memory Usage Risks**: High-frequency sampling and local filtering may exceed ESP32-S3 memory limits. **Severity: Major**

#### Recommendations:
- Optimize memory usage by profiling and limiting buffer sizes.

### 4. Reliability

#### Findings:
- **Fault Tolerance**: No defined behavior for sensor failures during runtime. **Severity: Major**

#### Recommendations:
- Implement fallback mechanisms for failed sensors.

### 5. Security

#### Findings:
- **Secure Boot**: No detailed mechanism for secure boot and firmware authenticity verification. **Severity: Critical**

#### Recommendations:
- Implement secure boot and cryptographic verification for firmware.

### 6. Maintainability

#### Findings:
- **Scalability**: Adding new sensors requires significant manual effort. **Severity: Minor**

#### Recommendations:
- Use a modular approach for sensor integration.

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## C. Missing / Risky Areas

### Missing System Requirements
- SD card wear leveling.
- Power loss recovery mechanisms.

### Missing System States
- Detailed ERROR and DEGRADED state transitions.

### Missing Failure Handling
- Sensor failure fallback mechanisms.

### Missing Documentation
- Secure boot and cryptographic key management.

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## D. Improvement Recommendations

1. **Architectural Enhancements**:
   - Enforce strict abstraction boundaries.
   - Define all state transitions and behaviors.

2. **Requirement Additions**:
   - Add requirements for SD card wear leveling and power loss recovery.

3. **Security Improvements**:
   - Implement secure boot and cryptographic verification mechanisms.

4. **Scalability Enhancements**:
   - Adopt a modular approach for sensor integration.

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## E. Generated Artifacts

### State Machine Diagram
```mermaid
graph TD
    INIT --> IDLE
    IDLE --> RUNNING
    RUNNING --> DEGRADED
    RUNNING --> ERROR
    DEGRADED --> TEARDOWN
    ERROR --> TEARDOWN
    TEARDOWN --> INIT
```

### Cross-Feature Conflict Table
| Feature A       | Feature B       | Conflict Description          | Resolution Recommendation       |
|-----------------|-----------------|-------------------------------|----------------------------------|
| OTA             | DAQ            | Timing conflicts              | Define OTA timing constraints   |
| Persistence     | Power Loss     | Data corruption risks         | Add wear leveling and recovery  |

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