FreeRTOS Concurrency & Thermals

The ESP32-SwitchBot architecture maximizes responsiveness while keeping power consumption and operational temperatures exceptionally low (~40°C).

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Dual-Core Task Segregation

The ESP32-S3 contains two Xtensa LX7 processor cores. Network operations and actuator controls are physically partitioned across cores:

┌───────────────────────────────────────────────────────────────────────────────┐
│                              ESP32-S3 SOC (80 MHz)                            │
├───────────────────────────────────────┬───────────────────────────────────────┤
│                CORE 0                 │                CORE 1                 │
├───────────────────────────────────────┼───────────────────────────────────────┤
│  • http_srv Task (Priority 4, 6 KB)   │  • arduino_loop Task (Priority 1, 8KB)│
│    - WebServer request dispatching    │    - Responsive 10ms loop scheduling  │
│    - Static cached /style.css & app.js│    - Instant async servo actuation    │
│    - Chunked HTTP streaming engine    │    - 60s NVS heartbeat persistence    │
│    - Zero-heap /api/live endpoint     │    - Wi-Fi failover & ARP keepalives  │
│  • ts_watchdog Task (Priority 1, 8KB) │  • ml_wg_mgr Task (Priority 6, 8 KB)  │
│    - Asynchronous Tailscale API checks│    - WireGuard ChaCha20-Poly1305      │
│  • ml_net_io Task (Priority 5, 6 KB)  │    - Handshake timers & peer sessions │
│    - DERP TLS socket transport        │                                       │
└───────────────────────────────────────┴───────────────────────────────────────┘

1. Core 0: Network & WebServer Operations

• http_srv Task (Priority 4): Dispatches incoming HTTP connections and streams chunked responses with a 2ms yield tick (vTaskDelay(pdMS_TO_TICKS(2))).
• ts_watchdog Task (Priority 1): Performs periodic HTTPS calls to api.tailscale.com in the background. Because it is completely decoupled from Core 1, blocking TLS handshakes never cause servo actuation lag.

2. Core 1: Control Loop & Servo Actuation

• arduino_loop Task (Priority 1): Manages physical actuator movements, NTP clock sync, Wi-Fi failover checks, 10-second Gratuitous ARP keepalives, and flash heartbeats.
• Asynchronous Actuation: When /trigger is called on Core 0, it signals Core 1 via FreeRTOS task notification (xTaskNotifyGive(loopTaskHandle)), responding to the client in < 5ms before the mechanical stroke completes.
• Zero-Jitter Priority Elevation: During physical stroke execution (triggerPress()), the task priority is dynamically elevated to priority 5 (above the http_srv task's priority 4), guaranteeing rock-solid hardware PWM timing free from network thread interruptions.

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Low-Power 80 MHz Clock & Tickless Idle

Standard ESP32 firmware runs at 240 MHz, consuming up to 800mW and generating chip temperatures of 60–70°C.

Why 80 MHz is the Sweet Spot:

1. Peripheral Stability: At 80 MHz, the internal APB bus operates at its native clock speed without baud rate drift on UART, SPI, or I2C.
2. Thermal Drop: Operating temperature falls from ~65°C to ~40°C, allowing safe enclosed mounting inside switch housings.
3. Power Consumption: Drops power draw to ~0.14 W (~28mA average current).
4. Tickless Idle: FreeRTOS automatically halts the CPU core via the waiti 0 instruction during idle periods between the 10ms scheduling cycles.