Execution Model

The stack utilizes a multi-tasking execution model managed by the VAIOS (Vayu Input/Output System) real-time kernel. This model ensures that high-frequency control loops, asynchronous communication, and background maintenance tasks coexist on a single microcontroller while satisfying strict real-time constraints.

Task Scheduling and Priorities

The system organizes functionality into discrete tasks, each assigned a priority level and an execution frequency. VAIOS employs a priority-based preemptive scheduler, ensuring that critical tasks can interrupt lower-priority operations to meet timing guarantees.

The task hierarchy is structured into three primary tiers:

• Tier 1: High-Priority Control (Priority 2): The bmx160_read task resides here. Since state estimation and control accuracy depend on precise sensor timing, sensor acquisition is given the highest precedence to minimize jitter.

• Tier 2: Real-Time Processing (Priority 1): This tier contains the Control Loops (Angle and Rate PID) and the Motor Output task. These tasks run at fixed intervals (e.g., 400 Hz to 1 kHz) and consume the data provided by Tier 1.

• Tier 3: Asynchronous Utilities (Priority 0): Lower-priority tasks such as comm_processor (telemetry), heartbeat, and logger. These tasks utilize the remaining CPU cycles to handle non-critical data exchange and system monitoring.

Execution Timing Diagram

Figure 3.5 illustrates the interleaved execution of high and low priority tasks over a single control cycle.

Deterministic Guarantees

By utilizing a hardware-backed DWT (Data Watchpoint and Trace) timer and the VAIOS scheduler, the system achieves sub-microsecond jitter for task wakeup. This determinism is critical for the stability of the inner PID loop, where even a few milliseconds of variance in the sampling interval ($dt$) can lead to oscillations or loss of control during aggressive maneuvers.