# Software Feature Specification

## SF-DATA: Persistence & Data Management

**Software Feature ID:** SF-DATA  
**Mapped System Feature:** F-DATA (Persistence & Data Management Features)  
**Version:** 1.0  
**Date:** 2025-02-01  

## 1. Feature Overview

The Persistence & Data Management software feature implements secure, reliable storage and retrieval of sensor data, system configuration, and diagnostic information. This feature provides the software implementation of persistent sensor data storage, data persistence abstraction, and safe data handling during system state transitions.

### 1.1 Mapped System Features

- **F-DATA-01**: Persistent Sensor Data Storage
- **F-DATA-02**: Data Persistence Abstraction (DP Component)
- **F-DATA-03**: Safe Data Handling During State Transitions
- **F-DATA-04**: Power-Loss Data Protection

## 2. Static View - Component Architecture

```mermaid
graph TB
    subgraph "Application Layer"
        DP[Data Pool]
        PERS[Persistence Manager]
    end
    
    subgraph "Storage Abstraction Layer"
        SA[Storage Abstraction]
        FC[File Controller]
        DC[Data Controller]
    end
    
    subgraph "Driver Layer"
        SD[SD Card Driver]
        NVM[NVM Driver]
        FS[File System]
    end
    
    subgraph "Hardware Abstraction"
        SPI[SPI Wrapper]
        FLASH[Flash Wrapper]
    end
    
    DP --> PERS
    PERS --> SA
    SA --> FC
    SA --> DC
    FC --> FS
    DC --> FS
    FS --> SD
    FS --> NVM
    SD --> SPI
    NVM --> FLASH
```

### 2.1 Component Interfaces

#### 2.1.1 Data Pool Interfaces

**Provided Interfaces:**
- `IDataPool`: Main data storage interface
- `IDataQuery`: Data retrieval interface
- `IDataSubscription`: Data change notification interface

**Required Interfaces:**
- `IPersistenceManager`: Persistent storage interface
- `IEventSystem`: Event notification interface

#### 2.1.2 Persistence Manager Interfaces

**Provided Interfaces:**
- `IPersistenceManager`: Persistence management interface
- `IStorageHealth`: Storage health monitoring interface
- `IDataIntegrity`: Data integrity verification interface

**Required Interfaces:**
- `IStorageAbstraction`: Storage layer interface
- `IFileSystem`: File system interface
- `IDiagnostics`: Diagnostic reporting interface

## 3. Dynamic View - Data Persistence Sequences

### 3.1 Sensor Data Storage Sequence

```mermaid
sequenceDiagram
    participant SM as Sensor Manager
    participant DP as Data Pool
    participant PM as Persistence Manager
    participant SA as Storage Abstraction
    participant FS as File System
    
    SM->>DP: storeSensorData(sensor_data)
    DP->>DP: validateData(sensor_data)
    DP->>PM: persistData(sensor_data)
    PM->>PM: formatRecord(sensor_data)
    PM->>SA: writeData(record)
    SA->>FS: writeFile(filename, data)
    FS-->>SA: write_result
    SA-->>PM: persistence_result
    PM-->>DP: operation_status
    DP->>DP: updateMemoryCache()
```

### 3.2 Safe Teardown Data Flush Sequence

```mermaid
sequenceDiagram
    participant STM as System State Manager
    participant DP as Data Pool
    participant PM as Persistence Manager
    participant SA as Storage Abstraction
    participant DIAG as Diagnostics
    
    STM->>DP: initiateTeardown()
    DP->>DP: stopDataIngestion()
    DP->>PM: flushAllBuffers()
    PM->>SA: syncAllData()
    SA->>SA: verifyDataIntegrity()
    SA-->>PM: flush_complete
    PM->>DIAG: logTeardownEvent()
    PM-->>DP: teardown_ready
    DP-->>STM: teardownComplete()
```

### 3.3 Power-Loss Protection Sequence

```mermaid
sequenceDiagram
    participant BOD as Brownout Detector
    participant PM as Persistence Manager
    participant DP as Data Pool
    participant SA as Storage Abstraction
    participant SC as Supercapacitor
    
    BOD->>PM: brownoutDetected()
    PM->>DP: emergencyFlush()
    DP->>PM: getCriticalData()
    PM->>SA: writeEmergencyData(critical_data)
    SA->>SA: fastWrite(data)
    Note over SC: Supercapacitor provides 1-2s runtime
    SA-->>PM: emergency_write_complete
    PM->>PM: enterSafeShutdown()
```

## 4. Software Constraints

### 4.1 Performance Constraints
- **SWC-DATA-001**: Data write operations must complete within 50ms for normal operation
- **SWC-DATA-002**: Emergency data flush must complete within 1 second during brownout
- **SWC-DATA-003**: Data retrieval operations must not block sensor acquisition

### 4.2 Resource Constraints
- **SWC-DATA-004**: Maximum data buffer size limited to 32KB per data type
- **SWC-DATA-005**: File system operations limited to 10 concurrent handles
- **SWC-DATA-006**: Storage wear-leveling must be implemented for SD card longevity

### 4.3 Reliability Constraints
- **SWC-DATA-007**: Data integrity verification required for all write operations
- **SWC-DATA-008**: Atomic write operations must be used to prevent corruption
- **SWC-DATA-009**: Storage health monitoring must detect and report failures

### 4.4 Security Constraints
- **SWC-DATA-010**: Sensitive data must be encrypted before storage
- **SWC-DATA-011**: Data access must be controlled through defined interfaces only
- **SWC-DATA-012**: Storage tampering detection mechanisms required

## 5. Traceability Matrix - Software Requirements

| Software Requirement ID | Feature Mapping | Component | Verification Method |
|-------------------------|-----------------|-----------|-------------------|
| SWR-DATA-001 | F-DATA-01 | Persistence Manager | Integration Test |
| SWR-DATA-002 | F-DATA-01 | Data Pool | Unit Test |
| SWR-DATA-003 | F-DATA-01 | Persistence Manager | Unit Test |
| SWR-DATA-004 | F-DATA-02 | Data Pool | Unit Test |
| SWR-DATA-005 | F-DATA-02 | Storage Abstraction | Unit Test |
| SWR-DATA-006 | F-DATA-02 | Persistence Manager | Unit Test |
| SWR-DATA-007 | F-DATA-03 | Persistence Manager | Integration Test |
| SWR-DATA-008 | F-DATA-03 | Data Pool | Unit Test |
| SWR-DATA-009 | F-DATA-03 | Storage Abstraction | Unit Test |
| SWR-DATA-010 | F-DATA-04 | Persistence Manager | Hardware Test |
| SWR-DATA-011 | F-DATA-04 | Persistence Manager | Hardware Test |
| SWR-DATA-012 | F-DATA-04 | Storage Abstraction | Performance Test |
| SWR-DATA-013 | F-DATA-04 | Persistence Manager | Unit Test |

## 6. Implementation Notes

### 6.1 Storage Architecture
- Dual storage support: SD Card (primary) and NVM (backup/critical data)
- File system: FAT32 for SD Card, NVS for NVM
- Data organization: Time-based directories for sensor data
- Retention policy: Configurable via Machine Constants

### 6.2 Data Integrity
- CRC32 checksums for all stored data records
- Atomic write operations using temporary files and rename
- Regular storage health checks and bad sector detection
- Automatic data recovery from backup storage when possible

### 6.3 Power-Loss Protection
- Hardware brownout detector at 3.0V threshold
- Supercapacitor provides 1-2 seconds of operation during power loss
- Critical data prioritization during emergency flush
- Fast write algorithms optimized for emergency scenarios

### 6.4 Data Organization
- Sensor data: `/data/sensors/YYYY/MM/DD/sensor_id.dat`
- Configuration: `/config/machine_constants.json`
- Diagnostics: `/logs/diagnostics/YYYY/MM/diagnostic.log`
- System state: `/state/system_state.dat`

### 6.5 Error Handling
- Storage failures trigger diagnostic events
- Automatic fallback to secondary storage medium
- Data corruption detection and recovery procedures
- Storage space monitoring and cleanup policies