Architecture

PAGE 7: System Architecture & Integration

System Architecture Overview

┌─────────────────────────────────────────────────────┐
│         Sensor Board (STM32H753ZI)                  │
│              480 MHz ARM Cortex-M7                  │
├─────────────────────────────────────────────────────┤
│                                                     │
│  ┌─────────────────────────────────────────────┐   │
│  │         FreeRTOS Kernel                     │   │
│  │   (CMSIS-RTOS V2 compatible)                │   │
│  │   64KB heap | 8KB stack min                 │   │
│  └─────────────────────────────────────────────┘   │
│              ↓                                      │
│  ┌─────────────────────────────────────────────┐   │
│  │         Main Sensor Task                    │   │
│  │   - Poll all sensors                        │   │
│  │   - Validate measurements                   │   │
│  │   - Build diagnostics                       │   │
│  │   - Send via UDP/Ethernet                   │   │
│  └─────────────────────────────────────────────┘   │
│         ↓                    ↓                      │
│  ┌──────────┐         ┌──────────────┐             │
│  │ Sensors  │         │   Packet     │             │
│  │          │         │  Dispatcher  │             │
│  │ ├─ GPS   │         │              │             │
│  │ ├─ IMU   │         │ (Incoming)   │             │
│  │ ├─ pH    │         └──────────────┘             │
│  │ ├─ Load  │                                      │
│  │ └─ Pres  │                                      │
│  └──────────┘                                      │
│         ↓                                           │
│  ┌─────────────────────────────────────────────┐   │
│  │  Protobuf Message Encoder                   │   │
│  │  (Nanopb library)                           │   │
│  └─────────────────────────────────────────────┘   │
│         ↓                                           │
│  ┌─────────────────────────────────────────────┐   │
│  │    UDP/Ethernet Stack (LwIP)                │   │
│  │  - MAC filtering (3 addresses)              │   │
│  │  - ARP management                           │   │
│  │  - Priority queues (2 levels)               │   │
│  └─────────────────────────────────────────────┘   │
│         ↓                                           │
└─────────────────────────────────────────────────────┘
           Network (192.168.0.x)
           UDP Port 7 (broadcast)

Main Loop Operation

while (1) {
    // STEP 1: System Health Check
    ├─ Check heap (critical: <8KB)
    ├─ Toggle status LEDs
    └─ Send raw Ethernet beacon
    
    // STEP 2: Initialize Diagnostics Message
    └─ SensorBoardDiagnostics diagnostics_msg
    
    // STEP 3: Poll All Sensors
    ├─ pH Sensor     // Poll and validate
    ├─ GPS Sensor    // Parse NMEA, validate
    ├─ IMU Sensor    // Read 3-axis data
    ├─ Load Cells    // Read and calibrate (×2)
    └─ Pressure Sensors  // Temperature compensate (×2)
    
    // STEP 4: Encode & Transmit
    ├─ Encode diagnostics to Protobuf
    ├─ Prepare UDP packet
    └─ Send broadcast (192.168.0.255:7)
    
    // STEP 5: Wait for Next Cycle
    └─ osDelay(5000 ms)  // 5 seconds
}

Error Handling Strategy

Polling Error States

if (poll_result == RESULT_ERR_UNIMPLEMENTED) {
    // Hardware not connected / not implemented
    sensor.state = SENSOR_IDLE;
    sensor.error_code = COMMUNICATION_FAILURE;
    
} else if (poll_result == RESULT_ERR_COMMS) {
    // I2C/UART/SPI communication error
    sensor.state = SENSOR_ERROR;
    sensor.error_code = COMMUNICATION_FAILURE;
    
} else if (poll_result == RESULT_OK) {
    // Data received, validate
    if (validate_sensor_data(value) == RESULT_OK) {
        sensor.state = SENSOR_OPERATING;
        sensor.error_code = NO_ERROR;
    } else {
        // Out of range / invalid
        sensor.state = SENSOR_ERROR;
        sensor.error_code = INVALID_DATA;
    }
}

Sensor Status Codes

Code	Meaning
SENSOR_IDLE	Not connected or not implemented
SENSOR_OPERATING	Normal operation, valid data
SENSOR_ERROR	Communication failure or invalid data

Initialization Sequence

Phase 1: Hardware Setup

1. MPU/Cache configuration
2. HAL initialization
3. System clock → 480 MHz
4. RTOS kernel init
5. GPIO initialization
6. Timer initialization (TIM1)

Phase 2: Communication Setup

1. UART initialization (115200 baud)
2. Logging system init
3. Ethernet PHY init (LAN8742)
4. MAC address filtering (3 addresses)
5. ARP table population

Phase 3: Application Setup

1. Packet dispatcher registration
2. All 6 sensor initializations
3. UDP queue creation (priority buffers)
4. UDP callback registration

Phase 4: Main Loop

1. LED initialization
2. Sensor polling starts
3. Continuous 5-second cycles

Memory Layout

Heap (64 KB total)
├─ Sensor data structures (~2 KB)
├─ Protobuf buffers (~4 KB)
├─ UDP TX queues (~16 KB)
├─ FreeRTOS kernel structures (~8 KB)
└─ Remaining free (~34 KB)

Critical Threshold: 8 KB
└─ Trigger when < 8KB detected