Chapter 8: FreeRTOS Multitasking Architecture

8.1 Key Points

• FreeRTOS task creation and core pinning on ESP32-S3
• Queue-based communication between tasks
• Mutex protection for shared data
• Separating sensor, control, and telemetry tasks

8.2 Course Content

A robot program should not place all logic inside a single loop. OSRCORE uses FreeRTOS tasks to separate RC input, sensor reading, control computation, and logging. This improves timing stability and makes the software easier to extend.

8.3 Basic Learning

Task Model

ESP32-S3 has two cores. ESP-IDF allows tasks to be pinned to a specific core:

xTaskCreatePinnedToCore(task_func, "task", 4096, NULL, 5, NULL, 0);

A typical split is:

Task	Responsibility
RC task	Receive and parse SBUS frames
Control task	Encoder feedback, PID calculation, ESC output
IMU task	Read and process IMU data
Telemetry task	Print logs and debug values

Queue and Mutex

• A queue transfers data between tasks safely.
• A mutex protects shared state from concurrent access.

8.4 Program Study

Create a queue:

typedef struct {
    uint16_t ch[16];
    bool failsafe;
} rc_frame_t;

QueueHandle_t rc_queue = xQueueCreate(4, sizeof(rc_frame_t));

Send from the SBUS task:

rc_frame_t frame;
if (sbus_read(&frame)) {
    xQueueSend(rc_queue, &frame, 0);
}

Receive in the control task:

rc_frame_t frame;
if (xQueueReceive(rc_queue, &frame, pdMS_TO_TICKS(20))) {
    if (!frame.failsafe) {
        // Convert channels to throttle and steering commands.
    }
}

8.5 Summary

FreeRTOS allows the robot firmware to remain responsive and modular. Queues and mutexes provide safe communication between tasks and avoid timing interference between unrelated work.

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