Aerosol Module Controller

System Architecture

The aerosol module controller implements a multi-threaded real-time control system on the Atmel AVR32 microcontroller. The firmware is structured into independent FreeRTOS tasks handling sensor acquisition, control algorithms, communication, and safety monitoring. Each task runs at its own priority level with deterministic timing guarantees.

Hardware Interface Layer

PWM Actuation & Control

Control Algorithms

Real-time Task Scheduler

/* FreeRTOS Task Definitions */

// Task 1: Sensor Acquisition (50 ms period, Priority=2)
void vTaskSensorMonitor(void *pvParameters) {
    while (1) {
        uint16_t raw_pressure = adc_read_pressure();
        uint16_t raw_temp = adc_read_temperature();
        uint8_t raw_flow = adc_read_flow_sensor();
        
        // Update global control state
        g_sensor_state.pressure_kpa = (raw_pressure / 4095.0f) * 200.0f;
        g_sensor_state.temp_celsius = (raw_temp / 4095.0f) * 134.0f;
        g_sensor_state.flow_percent = raw_flow;
        
        // Safety checks
        if (g_sensor_state.pressure_kpa > 220) {
            gpio_set_high(GPIO_SAFETY_SHUTDOWN);  // Emergency stop
        }
        
        vTaskDelay(pdMS_TO_TICKS(50));
    }
}

// Task 2: Control Loop (100 ms period, Priority=3)
void vTaskControlLoop(void *pvParameters) {
    while (1) {
        fog_concentration_control(g_setpoint.fog_percent);
        temperature_control(g_setpoint.temp_celsius);
        pressure_control(g_setpoint.pressure_kpa);
        
        vTaskDelay(pdMS_TO_TICKS(100));
    }
}

// Task 3: CANopen Communication (50 ms period, Priority=2)
void vTaskCANopen(void *pvParameters) {
    while (1) {
        // Transmit TPDO (Telemetry)
        can_send_tpdo1(g_sensor_state);
        
        // Process RPDO (Commands)
        canopen_rpdo_handler();
        
        vTaskDelay(pdMS_TO_TICKS(50));
    }
}

// Task 4: Safety Monitor (20 ms period, Priority=1 - Highest)
void vTaskSafetyMonitor(void *pvParameters) {
    while (1) {
        // Watchdog kick
        wdt_reload();
        
        // Fault detection
        if (g_sensor_state.pressure_kpa < 50) {
            fault_handler(FAULT_LOW_PRESSURE);
        }
        if (g_sensor_state.temp_celsius > 140) {
            fault_handler(FAULT_OVERTEMP);
        }
        
        vTaskDelay(pdMS_TO_TICKS(20));
    }
}

CANopen Communication Protocol

The firmware implements CANopen DS301 protocol for integration with the sterilizer control system. Telemetry (TPDO) transmits sensor measurements every 50 ms, while command reception (RPDO) updates setpoints from the main controller.

Safety & Fault Handling

• Watchdog Timer (WDT) — 1.5 second timeout with mandatory reload from highest-priority task. Guards against firmware lockup.
• Dual Sensor Redundancy — Pressure measured via two independent paths (direct + monitor line). Discrepancy triggers safe shutdown.
• Temperature Overshoot Protection — Heater cutoff at 135°C with 10-second cooldown before re-enable.
• Pressure Interlock — Flow valve disabled if pump duty < 10% to prevent cavitation.
• Brown-out Detection — BOD at 2.7V triggers controlled shutdown sequence to prevent Flash corruption.
• CAN Error Handling — Missing RPDO command for >500 ms triggers safe default state (all actuators to 0%).

Development Environment & Tools

• Compiler — Atmel Studio 7 with GCC ARM Embedded toolchain (arm-none-eabi-gcc 8.3.1)
• Hardware Debugger — JTAGICE3 (on-chip debugging, real-time trace)
• Simulation — QEMU AVR32 simulator for pre-hardware validation
• Code Analysis — Splint static analyzer + MISRA-C 2012 compliance checks
• Testing — Unity framework for unit tests; HIL with National Instruments PXI chassis

Memory Layout & Resource Allocation

// AVR32 UC3C Flash Allocation (256 KB)
0x00000000 — 0x00003FFF : Bootloader (16 KB)
0x00004000 — 0x0003FFFF : Application code + Data (228 KB)
0x00040000 — 0x00040FFF : EEPROM emulation (4 KB, wear-leveling)

// SRAM Allocation (64 KB)
0x20000000 — 0x2000FFFF : FreeRTOS heap + task stacks (20 KB)
0x20005000 — 0x200057FF : CAN message buffers (2 KB)
0x20006000 — 0x200067FF : ADC sample buffer (2 KB)
0x20007000 — 0x20007FFF : Persistent state storage (4 KB)

Performance Metrics & Timing Analysis