TCloop

TCloop, short for time-constrained loop, is a programming pattern used in real-time and embedded systems to execute a loop body at a predictable, fixed cadence. It supports deterministic timing by aligning iteration periods, which is critical for control tasks, sensor sampling, and synchronous audio or graphics processing.

In a typical TCloop, a period T defines the duration of each cycle. At the start of a cycle, a timer is read, the loop body executes, and the elapsed time is subtracted from T. If time remains, the system sleeps or yields to preserve the cadence; if the loop overruns, a deadline miss is logged and corrective measures may be taken, such as skipping nonessential work, adjusting scheduling, or signaling an upstream monitor.

TCloop can be implemented within a hard real-time or soft real-time context. Variants differ in how strictly deadlines must be met and how jitter is managed. Implementation considerations include the choice of timer source, minimizing critical sections, avoiding blocking calls, and ensuring appropriate task priorities in a real-time operating system. Hardware timers, interrupts, and synchronization primitives all influence accuracy and robustness.

Applications include robotics control loops, motor controllers, data acquisition, audio and video processing pipelines, and game engines with fixed-frame-rate updates. Related concepts include fixed-step loops, real-time scheduling, and time-triggered architectures. See also Real-time operating system, fixed-step loop, deadline scheduling.