## 1\. Purpose

This document defines **cross-feature constraints** that apply across multiple system features and components. These constraints ensure consistent behavior, prevent architectural violations, and reduce integration risk.

Cross-feature constraints are **mandatory rules** that all future software design and implementation must comply with.

## 2\. Architectural Constraints

### CFC-ARCH-01: Layered Architecture Enforcement

*   Application logic shall not access hardware directly.
    
*   All hardware access shall be performed via Drivers and OSAL layers.
    
*   Persistence access shall only be performed through the DP component.
    

**Impacted Features:**  
DAQ, DQC, DATA, DIAG, SYS, OTA, SEC

### CFC-ARCH-02: State-Aware Feature Execution

*   All features shall be aware of the current system state.
    
*   Features shall not execute actions that are invalid for the current state.
    

**Examples:**

*   DAQ shall not start sampling during OTA\_UPDATE.
    
*   Communication shall be limited during TEARDOWN.
    

**Impacted Features:**  
SYS, DAQ, COM, OTA, DATA

## 3\. Concurrency & Timing Constraints

### CFC-TIME-01: Non-Blocking Operation

*   Sensor acquisition, communication, and UI updates shall be non-blocking.
    
*   Blocking operations shall be isolated in controlled system services (e.g., persistence task).
    

**Impacted Features:**  
DAQ, COM, SYS

### CFC-TIME-02: Deterministic Task Behavior

*   Time-critical tasks (sensor acquisition, watchdog servicing) shall have deterministic execution time.
    
*   Dynamic memory allocation during runtime shall be minimized or prohibited in critical paths.
    

**Impacted Features:**  
DAQ, SYS, DIAG

## 4\. Data & Persistence Constraints

### CFC-DATA-01: Single Source of Truth

*   Runtime and persistent data shall be owned and managed by the DP component.
    
*   No feature shall maintain private persistent copies of shared system data.
    

**Impacted Features:**  
DATA, DAQ, DIAG, SYS, OTA

### CFC-DATA-02: Data Consistency During Transitions

*   No data write operations shall occur during teardown unless explicitly authorized by the System Manager.
    
*   Persistence completion shall be confirmed before state transitions.
    

**Impacted Features:**  
SYS, DATA, OTA

## 5\. Security Constraints

### CFC-SEC-01: Security First Initialization

*   Secure boot and flash protection shall be enabled before any application-level logic executes.
    

**Impacted Features:**  
SEC, SYS

### CFC-SEC-02: Encrypted Channels Only

*   OTA, diagnostics, and data transmission shall only occur over encrypted and authenticated channels.
    

**Impacted Features:**  
COM, OTA, DIAG, SEC

## 6\. HMI & Debug Constraints

### CFC-HMI-01: Read-Only Local UI

*   The OLED HMI shall not allow configuration changes that affect system safety or security.
    
*   Configuration updates shall only be accepted via authenticated communication channels.
    

**Impacted Features:**  
SYS, SEC

### CFC-DBG-01: Debug Isolation

*   Debug and engineering sessions shall not interfere with normal system operation.
    
*   Debug commands shall respect system state restrictions.
    

**Impacted Features:**  
SYS, DIAG, SEC