System Requirements Specification

Document ID: SRS-ESP32-DISTANCE
Version: 1.0
Date: 2025-07-24
Author: ESP32 Distance Project Team

Document Purpose

This document specifies the high-level system requirements for the ESP32 Distance Sensor project, following OpenFastTrack (OFT) methodology for requirements engineering and traceability.

System Overview

The ESP32 Distance Sensor system is an IoT device that:

Measures distance using HC-SR04 ultrasonic sensor
Displays distance on WS2812 LED strip
Provides WiFi connectivity and web interface
Supports runtime configuration and monitoring

Requirements Traceability

Requirement ID	Design Reference	Priority
REQ-SYS-1	DSN-SYS-1	Mandatory
REQ-SYS-2	DSN-SYS-2	Mandatory
REQ-SYS-3	DSN-SYS-3	Mandatory
REQ-SYS-4	DSN-SYS-4	Mandatory
REQ-SYS-5	DSN-SYS-5	Mandatory
REQ-SYS-6	DSN-SYS-6	Mandatory
REQ-SYS-7	DSN-SYS-7	Mandatory
REQ-SYS-8	DSN-SYS-8	Mandatory
REQ-SYS-SIM-1	DSN-SIM-LED-01, DSN-SIM-SNS-01	Mandatory

Requirement Categories

Requirements are categorized using the following prefixes:

REQ-SYS: System-level requirements
REQ-CFG: Configuration management requirements
REQ-SEN: Sensor requirements
REQ-LED: LED display requirements
REQ-NET: Network and connectivity requirements
REQ-WEB: Web interface requirements

System Requirements

REQ-SYS-1: ESP32 Hardware Platform

Type: System
Priority: Mandatory
Description: The system SHALL operate on ESP32 WROOM-32F microcontroller with 4MB flash memory.

Rationale: ESP32 provides WiFi connectivity, sufficient processing power, and adequate flash memory for the application.

Acceptance Criteria:

AC-1: System boots successfully on ESP32 WROOM-32F
AC-2: Flash usage does not exceed 90% of available 4MB
AC-3: System operates within ESP32 memory constraints

REQ-SYS-2: Real-time Distance Measurement

Type: Functional
Priority: Mandatory
Description: The system SHALL continuously measure distance and update LED display in real-time.

Rationale: Core functionality for distance visualization and monitoring.

Acceptance Criteria:

AC-1: Distance measurements updated at minimum 10Hz frequency
AC-2: LED display reflects distance changes within 100ms
AC-3: System maintains real-time performance under all operating conditions

REQ-SYS-3: WiFi Connectivity

Type: Functional
Priority: Mandatory
Description: The system SHALL provide WiFi connectivity in both Access Point (AP) and Station (STA) modes.

Rationale: Enables web interface access and network configuration.

Acceptance Criteria:

AC-1: System creates WiFi Access Point for initial configuration
AC-2: System connects to existing WiFi networks as station
AC-3: Automatic fallback to AP mode if STA connection fails

REQ-SYS-4: Web-based Configuration

Type: Functional
Priority: Mandatory
Description: The system SHALL provide web interface for configuration and monitoring.

Rationale: User-friendly interface for system setup and operation.

Acceptance Criteria:

AC-1: Web interface accessible via HTTP
AC-2: Configuration changes applied without firmware recompilation
AC-3: Real-time monitoring of system status and sensor data

REQ-SYS-5: Non-volatile Configuration Storage

Type: Functional
Priority: Mandatory
Description: The system SHALL persist configuration settings across power cycles.

Rationale: Maintains user settings and system configuration permanently.

Acceptance Criteria:

AC-1: Configuration survives device reset and power loss
AC-2: Factory reset capability restores default settings
AC-3: Configuration corruption detection and recovery

REQ-SYS-6: Component-based Architecture

Type: Design
Priority: Mandatory
Description: The system SHALL implement modular component-based architecture.

Rationale: Enables maintainability, testability, and reusability.

Acceptance Criteria:

AC-1: Distance sensor implemented as independent component
AC-2: LED controller implemented as independent component
AC-3: Components provide well-defined APIs
AC-4: Main application coordinates components without tight coupling

REQ-SYS-7: Error Handling and Recovery

Type: Reliability
Priority: Mandatory
Description: The system SHALL handle errors gracefully and attempt recovery.

Rationale: Ensures system reliability and user experience.

Acceptance Criteria:

AC-1: Sensor timeouts handled without system crash
AC-2: WiFi connection failures trigger automatic retry
AC-3: System logs errors for diagnostics
AC-4: Watchdog timer prevents system hang

REQ-SYS-8: Memory Management

Type: Performance
Priority: Mandatory
Description: The system SHALL manage memory efficiently within ESP32 constraints.

Rationale: Prevents memory leaks and ensures stable operation.

Acceptance Criteria:

AC-1: Heap usage monitored and bounded
AC-2: No memory leaks during normal operation
AC-3: Stack overflow protection for all tasks
AC-4: Dynamic allocation minimized in time-critical paths

REQ-SYS-SIM-1: Emulator / Simulator Build Support

Type: Design / Testability

Priority: Mandatory

Description: The system SHALL provide a build-time selectable emulator/simulator mode that replaces hardware-near modules with simulator implementations while preserving the public component APIs and runtime behavior seen by higher-level modules. Simulator implementations MUST be selectable without modifying header files or higher-level application code.

Rationale: Enables development and testing on host environments (QEMU) without physical hardware, improves reproducibility and CI test coverage, and enforces clean module boundaries that encapsulate hardware dependencies.

Acceptance Criteria:

AC-1: A Kconfig option CONFIG_TARGET_EMULATOR (or equivalent) exists to enable emulator builds via menuconfig or idf.py -DCONFIG_TARGET_EMULATOR=1 build.
AC-2: Simulator implementations are selected by the buildsystem (CMake) and compiled in place of hardware implementations (example: distance_sensor_sim.c vs distance_sensor.c) without requiring changes to header files or higher-layer code.
AC-3: Simulator components MUST implement the complete public API of their hardware counterparts and return identical error codes and semantics for consumers (blocking queue semantics, return values, state queries).
AC-4: The distance sensor simulator SHALL produce deterministic measurements performing a linear sweep from 5cm to 60cm and back with 1mm resolution, advancing once per second; measurements are published on the processed measurement queue using the same distance_measurement_t structure and status codes.
AC-5: The LED controller simulator SHALL maintain the same in-RAM buffer semantics and led_show() API; physical transmission is replaced by a rate-limited terminal visualization (≈1Hz) using unobtrusive symbols (emoji or ASCII) to reflect per-pixel state.
AC-6: The web server and WiFi manager MAY be left unchanged in emulator builds; lack of real WiFi events is acceptable and must not cause crashes. The emulator requirement does not mandate network stack simulation in the first iteration.
AC-7: The emulator build SHALL be runnable under QEMU (or a documented emulator) and produce observable LED visualization and distance measurement output in the serial console.
AC-8: Documentation in docs/design/ and docs/requirements/ updated to reference simulator design artifacts and provide build/run verification steps.

Compliance and Validation

Traceability

All requirements SHALL be traceable to:

Design specifications in docs/design/
Implementation in main/ and components/
Test cases in docs/test/

Validation Method

Inspection: Code review and documentation review
Testing: Unit tests, integration tests, system tests
Analysis: Static analysis and memory profiling
Demonstration: Live system demonstration

Change Management

Requirements changes tracked through Git version control
Impact analysis performed for all requirement modifications
Traceability updated when requirements change
Approval required for mandatory requirement changes

This document follows OpenFastTrack methodology for requirements engineering and traceability.