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+# System Requirements Specification (SRS)
+# ASF Sensor Hub (Sub-Hub) Embedded System
+
+**Document Type:** System Requirements Specification  
+**Version:** 1.0  
+**Date:** 2025-01-19  
+**Platform:** ESP32-S3, ESP-IDF v5.4, C/C++  
+**Domain:** Industrial/Agricultural Automation (Smart Poultry Farm)  
+**Standard:** ISO/IEC/IEEE 29148:2018  
+
+## 1. Introduction
+
+### 1.1 Purpose
+
+This System Requirements Specification (SRS) defines the complete set of system requirements for the ASF Sensor Hub (Sub-Hub) embedded system. The document serves as the authoritative source for all functional and non-functional requirements that the system must satisfy.
+
+### 1.2 Scope
+
+The ASF Sensor Hub is a distributed sensing node deployed inside a poultry house for environmental monitoring and data collection. The system is responsible for:
+
+- Acquisition of multiple environmental sensor data
+- Local preprocessing and validation of sensor data
+- Persistent storage of data and configuration
+- Secure communication with a Main Hub
+- Support for diagnostics, maintenance, and OTA updates
+- Safe operation under fault conditions
+
+**Explicitly out of scope:**
+- Main Hub processing and control logic
+- Cloud analytics and services
+- Farm control algorithms
+- Actuator management
+
+### 1.3 Definitions and Acronyms
+
+| Term | Definition |
+|------|------------|
+| **Sub-Hub** | The ASF Sensor Hub embedded system (this system) |
+| **Main Hub** | Central processing unit that coordinates multiple Sub-Hubs |
+| **MC** | Machine Constants - persistent configuration data |
+| **DP** | Data Persistence component |
+| **STM** | State Manager component |
+| **SAL** | Sensor Abstraction Layer |
+| **HMI** | Human-Machine Interface (OLED display + buttons) |
+| **OTA** | Over-The-Air firmware update |
+| **mTLS** | Mutual Transport Layer Security |
+| **CBOR** | Concise Binary Object Representation |
+
+### 1.4 References
+
+- ISO/IEC/IEEE 29148:2018 - Systems and software engineering — Life cycle processes — Requirements engineering
+- IEC 61508 - Functional safety of electrical/electronic/programmable electronic safety-related systems
+- ESP-IDF v5.4 Programming Guide
+- System_Architecture_Documentation.md
+- Cross-Feature Constraints.md
+
+## 2. Overall Description
+
+### 2.1 Product Perspective
+
+The ASF Sensor Hub operates as an autonomous embedded system within a distributed poultry farm automation network. It interfaces with:
+
+- **Environmental sensors** via I2C, SPI, UART, and analog interfaces
+- **Main Hub** via encrypted Wi-Fi communication
+- **Peer Sub-Hubs** via ESP-NOW for limited coordination
+- **Local operators** via OLED display and button interface
+- **SD Card** for persistent data storage
+
+### 2.2 Product Functions
+
+The system provides the following major functions:
+
+1. **Multi-sensor data acquisition** with high-frequency sampling and filtering
+2. **Data quality assurance** through calibration and failure detection
+3. **Secure communication** with Main Hub using encrypted protocols
+4. **Persistent data storage** with wear-aware management
+5. **Over-the-air firmware updates** with rollback capability
+6. **Comprehensive diagnostics** and health monitoring
+7. **Local human-machine interface** for status and diagnostics
+8. **System state management** with controlled transitions
+9. **Security enforcement** through hardware-based protection
+10. **Power and fault handling** with graceful degradation
+
+### 2.3 User Classes and Characteristics
+
+| User Class | Characteristics | System Interaction |
+|------------|-----------------|-------------------|
+| **Farm Operators** | Basic technical knowledge, daily monitoring | Local HMI for status checking |
+| **Maintenance Engineers** | Advanced technical knowledge, periodic maintenance | Debug sessions, diagnostic access |
+| **System Integrators** | Expert technical knowledge, system configuration | Machine constants management, OTA updates |
+
+### 2.4 Operating Environment
+
+- **Hardware Platform:** ESP32-S3 microcontroller
+- **Operating System:** FreeRTOS (via ESP-IDF)
+- **Development Framework:** ESP-IDF v5.4
+- **Programming Language:** C/C++
+- **Environmental Conditions:** Industrial poultry house (temperature, humidity, dust)
+- **Power Supply:** 12V DC with brownout protection
+- **Communication:** Wi-Fi 802.11n (2.4 GHz), ESP-NOW
+
+### 2.5 Design and Implementation Constraints
+
+- **Memory:** 512KB SRAM, 8MB Flash (ESP32-S3)
+- **Real-time:** Deterministic sensor sampling within 1-second cycles
+- **Security:** Hardware-enforced Secure Boot V2 and Flash Encryption
+- **Reliability:** 99.9% uptime requirement in normal operating conditions
+- **Safety:** IEC 61508 SIL-1 compliance for sensor data integrity
+- **Environmental:** IP65 enclosure rating, -10°C to +60°C operating range
+
+## 3. System Requirements
+
+### 3.1 Functional Requirements
+
+#### 3.1.1 Sensor Data Acquisition Requirements
+
+**SR-DAQ-001: Multi-Sensor Support**  
+The system SHALL support simultaneous data acquisition from the following sensor types:
+- Temperature sensors
+- Humidity sensors  
+- Carbon Dioxide (CO₂) sensors
+- Ammonia (NH₃) sensors
+- Volatile Organic Compounds (VOC) sensors
+- Particulate Matter (PM) sensors
+- Light Intensity sensors
+
+**SR-DAQ-002: High-Frequency Sampling**  
+The system SHALL sample each enabled sensor a minimum of 10 times per acquisition cycle to enable local filtering.
+
+**SR-DAQ-003: Local Data Filtering**  
+The system SHALL apply configurable filtering algorithms (median filter, moving average) to raw sensor samples to produce representative values.
+
+**SR-DAQ-004: Timestamped Data Generation**  
+The system SHALL associate each processed sensor value with a timestamp accurate to ±1 second of system time.
+
+**SR-DAQ-005: Sensor State Management**  
+The system SHALL maintain operational state for each sensor (enabled/disabled, present/absent, healthy/faulty).
+
+#### 3.1.2 Data Quality & Calibration Requirements
+
+**SR-DQC-001: Automatic Sensor Detection**  
+The system SHALL automatically detect the presence of sensors based on hardware detection signals during initialization and runtime.
+
+**SR-DQC-002: Sensor Type Enforcement**  
+The system SHALL enforce sensor-slot compatibility to prevent incorrect sensor installation and usage.
+
+**SR-DQC-003: Sensor Failure Detection**  
+The system SHALL detect sensor failures including communication errors, out-of-range values, and non-responsive sensors.
+
+**SR-DQC-004: Machine Constants Management**  
+The system SHALL maintain persistent Machine Constants (MC) data including:
+- Installed sensor type definitions
+- Sensor calibration parameters
+- Communication configuration parameters
+- System identity parameters
+
+**SR-DQC-005: Calibration Parameter Application**  
+The system SHALL apply calibration parameters from MC data to raw sensor readings to produce calibrated values.
+
+#### 3.1.3 Communication Requirements
+
+**SR-COM-001: Main Hub Communication**  
+The system SHALL provide bidirectional encrypted communication with a Main Hub to:
+- Send sensor data using CBOR encoding
+- Send diagnostic information
+- Receive configuration updates
+- Receive firmware updates
+
+**SR-COM-002: Secure Communication Protocols**  
+The system SHALL use mTLS 1.2 with X.509 certificates for all Main Hub communication.
+
+**SR-COM-003: On-Demand Data Broadcasting**  
+The system SHALL transmit the most recent sensor dataset upon request from the Main Hub within 5 seconds.
+
+**SR-COM-004: Peer Communication**  
+The system SHALL support limited peer-to-peer communication with other Sub-Hubs using ESP-NOW for:
+- Connectivity checks
+- Time synchronization support
+- Basic status exchange
+
+**SR-COM-005: Communication Fault Tolerance**  
+The system SHALL continue autonomous operation during Main Hub communication failures for up to 24 hours.
+
+#### 3.1.4 Persistence & Data Management Requirements
+
+**SR-DATA-001: Persistent Sensor Data Storage**  
+The system SHALL store sensor data persistently on SD Card using FAT32 file system with wear-aware batch writing.
+
+**SR-DATA-002: Data Persistence Abstraction**  
+The system SHALL provide a unified Data Persistence (DP) component that abstracts storage media access for all persistent data operations.
+
+**SR-DATA-003: Safe Data Handling During Transitions**  
+The system SHALL ensure all critical data is safely persisted before:
+- Firmware updates
+- Configuration updates  
+- System teardown
+- Reset or restart operations
+
+**SR-DATA-004: Data Integrity Protection**  
+The system SHALL implement data integrity mechanisms including checksums and atomic write operations to prevent data corruption.
+
+**SR-DATA-005: Storage Capacity Management**  
+The system SHALL manage storage capacity by implementing circular logging with configurable retention periods.
+
+#### 3.1.5 Firmware Update (OTA) Requirements
+
+**SR-OTA-001: OTA Update Negotiation**  
+The system SHALL implement an OTA handshake mechanism with the Main Hub to acknowledge update availability and signal readiness.
+
+**SR-OTA-002: Firmware Reception and Storage**  
+The system SHALL securely receive firmware images and store them temporarily on SD Card before activation.
+
+**SR-OTA-003: Firmware Integrity Validation**  
+The system SHALL validate firmware integrity using SHA-256 checksums before activation.
+
+**SR-OTA-004: Safe Firmware Activation**  
+The system SHALL implement A/B partitioning with automatic rollback capability for safe firmware activation.
+
+**SR-OTA-005: OTA State Management**  
+The system SHALL coordinate OTA operations with the system state machine to ensure safe transitions and data preservation.
+
+#### 3.1.6 Security & Safety Requirements
+
+**SR-SEC-001: Secure Boot**  
+The system SHALL implement Secure Boot V2 to ensure only authenticated firmware is executed.
+
+**SR-SEC-002: Flash Encryption**  
+The system SHALL implement Flash Encryption using AES-256 to protect sensitive data and intellectual property.
+
+**SR-SEC-003: Certificate Management**  
+The system SHALL manage X.509 certificates for mTLS communication with secure storage and validation.
+
+**SR-SEC-004: Security Violation Handling**  
+The system SHALL detect and respond to security violations including:
+- Boot verification failures
+- Certificate validation failures
+- Unauthorized access attempts
+
+#### 3.1.7 Diagnostics & Health Monitoring Requirements
+
+**SR-DIAG-001: Diagnostic Code Management**  
+The system SHALL implement structured diagnostics with:
+- Unique diagnostic codes (format: 0xSCCC)
+- Severity levels (INFO, WARNING, ERROR, FATAL)
+- Root cause hierarchy
+- Timestamp information
+
+**SR-DIAG-002: Diagnostic Data Storage**  
+The system SHALL persistently store diagnostic events in a circular log with configurable retention.
+
+**SR-DIAG-003: Diagnostic Session Support**  
+The system SHALL provide diagnostic sessions allowing authorized engineers to:
+- Retrieve diagnostic data
+- Inspect system health status
+- Clear diagnostic records
+
+**SR-DIAG-004: Layered Watchdog System**  
+The system SHALL implement multiple watchdog levels:
+- Task-level watchdogs for critical tasks
+- Interrupt watchdog for system responsiveness
+- RTC watchdog for ultimate system recovery
+
+#### 3.1.8 System Management Requirements
+
+**SR-SYS-001: System State Machine**  
+The system SHALL implement a finite state machine with the following states:
+- INIT, BOOT_FAILURE, RUNNING, WARNING, FAULT
+- OTA_PREP, OTA_UPDATE, MC_UPDATE, TEARDOWN
+- SERVICE, SD_DEGRADED
+
+**SR-SYS-002: State-Aware Operation**  
+The system SHALL restrict feature operations based on current system state according to defined state transition rules.
+
+**SR-SYS-003: Controlled Teardown**  
+The system SHALL execute a controlled teardown sequence that:
+- Stops sensor acquisition
+- Flushes all critical data
+- Ensures storage consistency
+- Prepares for target state transition
+
+**SR-SYS-004: Local Human-Machine Interface**  
+The system SHALL provide local status indication using:
+- OLED display (128x64, I2C interface)
+- Three-button navigation (Up, Down, Select)
+- Menu system for diagnostics and sensor status
+
+**SR-SYS-005: Engineering Access**  
+The system SHALL support authenticated engineering sessions for:
+- Log inspection
+- Machine constants inspection and update
+- Controlled debugging operations
+
+#### 3.1.9 Power & Fault Handling Requirements
+
+**SR-PWR-001: Brownout Detection**  
+The system SHALL detect power supply brownout conditions and initiate controlled shutdown procedures.
+
+**SR-PWR-002: Power-Loss Recovery**  
+The system SHALL implement power-loss recovery mechanisms to restore operation after power restoration.
+
+**SR-PWR-003: Fault Classification**  
+The system SHALL classify faults into categories:
+- Sensor faults, Communication faults, Storage faults
+- Power faults, Security faults, Software faults, Hardware faults
+
+**SR-PWR-004: Fault Escalation**  
+The system SHALL implement fault escalation procedures based on severity and frequency.
+
+#### 3.1.10 Hardware Abstraction Requirements
+
+**SR-HW-001: Sensor Abstraction Layer**  
+The system SHALL implement a Sensor Abstraction Layer (SAL) that provides uniform interfaces for different sensor types.
+
+**SR-HW-002: Hardware Interface Abstraction**  
+The system SHALL abstract hardware interfaces (GPIO, I2C, SPI, UART, ADC) through driver layers to enable portability.
+
+**SR-HW-003: GPIO Discipline**  
+The system SHALL implement GPIO discipline with defined ownership and access control for hardware resources.
+
+### 3.2 Non-Functional Requirements
+
+#### 3.2.1 Performance Requirements
+
+**SR-PERF-001: Sensor Acquisition Timing**  
+The system SHALL complete sensor acquisition cycles within 1 second for all enabled sensors.
+
+**SR-PERF-002: Communication Response Time**  
+The system SHALL respond to Main Hub requests within 5 seconds under normal operating conditions.
+
+**SR-PERF-003: Memory Usage**  
+The system SHALL operate within 80% of available SRAM (409.6KB) and Flash (6.4MB) capacity.
+
+**SR-PERF-004: Storage Performance**  
+The system SHALL achieve minimum 10KB/s write performance to SD Card for data logging.
+
+#### 3.2.2 Reliability Requirements
+
+**SR-REL-001: System Availability**  
+The system SHALL achieve 99.9% availability during normal operating conditions.
+
+**SR-REL-002: Mean Time Between Failures**  
+The system SHALL achieve MTBF of 8760 hours (1 year) under specified environmental conditions.
+
+**SR-REL-003: Fault Recovery**  
+The system SHALL automatically recover from transient faults within 30 seconds.
+
+**SR-REL-004: Data Integrity**  
+The system SHALL maintain data integrity with error rate < 1 in 10^6 operations.
+
+#### 3.2.3 Safety Requirements
+
+**SR-SAFE-001: Fail-Safe Operation**  
+The system SHALL fail to a safe state (sensor data marked invalid) upon detection of critical faults.
+
+**SR-SAFE-002: Sensor Data Validation**  
+The system SHALL validate sensor data ranges and mark out-of-range values as invalid.
+
+**SR-SAFE-003: Watchdog Protection**  
+The system SHALL implement multiple watchdog mechanisms to detect and recover from software failures.
+
+#### 3.2.4 Security Requirements
+
+**SR-SEC-005: Authentication**  
+The system SHALL authenticate all external communication using certificate-based mutual authentication.
+
+**SR-SEC-006: Data Encryption**  
+The system SHALL encrypt all sensitive data at rest using AES-256 encryption.
+
+**SR-SEC-007: Secure Communication**  
+The system SHALL encrypt all network communication using TLS 1.2 or higher.
+
+**SR-SEC-008: Access Control**  
+The system SHALL implement role-based access control for engineering and diagnostic functions.
+
+#### 3.2.5 Maintainability Requirements
+
+**SR-MAINT-001: Diagnostic Accessibility**  
+The system SHALL provide comprehensive diagnostic information accessible through local and remote interfaces.
+
+**SR-MAINT-002: Configuration Management**  
+The system SHALL support field configuration updates through authenticated channels.
+
+**SR-MAINT-003: Firmware Updateability**  
+The system SHALL support secure over-the-air firmware updates with rollback capability.
+
+#### 3.2.6 Portability Requirements
+
+**SR-PORT-001: Hardware Abstraction**  
+The system SHALL abstract hardware dependencies to enable porting to compatible microcontroller platforms.
+
+**SR-PORT-002: Standard Interfaces**  
+The system SHALL use standard communication protocols (I2C, SPI, UART) for sensor interfaces.
+
+### 3.3 Interface Requirements
+
+#### 3.3.1 Hardware Interfaces
+
+**SR-HW-IF-001: Sensor Interfaces**  
+The system SHALL provide the following sensor interfaces:
+- 4x I2C interfaces for digital sensors
+- 2x SPI interfaces for high-speed sensors  
+- 2x UART interfaces for serial sensors
+- 4x ADC channels for analog sensors
+
+**SR-HW-IF-002: Communication Interfaces**  
+The system SHALL provide:
+- Wi-Fi 802.11n (2.4 GHz) interface
+- Optional Zigbee/LoRa interface for backup communication
+
+**SR-HW-IF-003: Storage Interfaces**  
+The system SHALL provide:
+- SD Card interface (SPI-based)
+- Internal NVM (encrypted)
+
+**SR-HW-IF-004: User Interface**  
+The system SHALL provide:
+- OLED display interface (I2C, 128x64 pixels)
+- 3x GPIO inputs for buttons (Up, Down, Select)
+
+#### 3.3.2 Software Interfaces
+
+**SR-SW-IF-001: Main Hub Protocol**  
+The system SHALL implement the Main Hub communication protocol using:
+- MQTT over TLS 1.2 transport
+- CBOR message encoding
+- Defined message schemas for sensor data, diagnostics, and control
+
+**SR-SW-IF-002: Peer Communication Protocol**  
+The system SHALL implement peer communication using ESP-NOW protocol with defined message formats.
+
+**SR-SW-IF-003: Diagnostic Interface**  
+The system SHALL provide diagnostic interface supporting:
+- Log retrieval commands
+- System status queries
+- Configuration inspection commands
+
+## 4. System Architecture Requirements
+
+### 4.1 Architectural Constraints
+
+**SR-ARCH-001: Layered Architecture**  
+The system SHALL implement a strict layered architecture with dependency flow from Application → Drivers → OSAL → HAL.
+
+**SR-ARCH-002: Hardware Abstraction**  
+Application logic SHALL NOT access hardware directly and SHALL use driver abstractions exclusively.
+
+**SR-ARCH-003: State-Aware Execution**  
+All system features SHALL be aware of current system state and respect state-based operation restrictions.
+
+**SR-ARCH-004: Event-Driven Communication**  
+Internal component communication SHALL use event-driven publish/subscribe mechanisms.
+
+**SR-ARCH-005: Data Persistence Abstraction**  
+All persistent data access SHALL be performed through the Data Persistence (DP) component.
+
+### 4.2 Component Requirements
+
+**SR-COMP-001: State Manager Component**  
+The system SHALL implement a State Manager (STM) component responsible for:
+- System state machine implementation
+- State transition validation and coordination
+- Teardown sequence management
+
+**SR-COMP-002: Event System Component**  
+The system SHALL implement an Event System component providing:
+- Publish/subscribe event bus
+- Non-blocking event delivery
+- Event type management
+
+**SR-COMP-003: Sensor Manager Component**  
+The system SHALL implement a Sensor Manager component responsible for:
+- Sensor lifecycle management
+- Data acquisition scheduling
+- Local filtering and validation
+
+**SR-COMP-004: Data Persistence Component**  
+The system SHALL implement a Data Persistence (DP) component providing:
+- Storage media abstraction
+- Data serialization/deserialization
+- Wear-aware storage management
+
+## 5. Verification Requirements
+
+### 5.1 Verification Methods
+
+Each system requirement SHALL be verified using one or more of the following methods:
+- **Test (T):** Verification by test execution
+- **Analysis (A):** Verification by analysis or calculation  
+- **Inspection (I):** Verification by inspection or review
+- **Demonstration (D):** Verification by demonstration
+
+### 5.2 Verification Levels
+
+- **Unit Level:** Individual component verification
+- **Integration Level:** Component interaction verification
+- **System Level:** End-to-end system verification
+- **Acceptance Level:** User acceptance verification
+
+## 6. Traceability
+
+This SRS provides the foundation for:
+- Software Requirements Specification (SWR-XXX requirements)
+- Feature specifications (F-XXX features)
+- Component specifications (C-XXX components)
+- Test specifications and procedures
+
+All system requirements SHALL be traceable to:
+- Stakeholder needs and use cases
+- Feature definitions in Features.md
+- Architectural constraints in Cross-Feature Constraints.md
+
+---
+
+**Document Status:** Final for Implementation Phase  
+**Next Review:** After Software Requirements Specification completion