Real-time systems focus on achieving fast response time, which, however, is usually accompanied by sacrificing the predictability. The Logical Execution Time (LET) model achieves I/O-predictability by fixing the timing of reading inputs and writing outputs. However, LET lacks the mechanism to react to aperiodic requests which have frequently been used in soft real-time applications. To improve aperiodic responsiveness as well as obtain predictability, in this paper, we present a component-based LET extension-Clockwerk. Clockwerk introduces the concept of Servant as basic components to make both communication and computation parts of periodic tasks predictable. By combining the LET model with the aperiodic server, Clockwerk achieves the improvement of aperiodic responsiveness. Consequently, our proposal can reduce the complexity of schedulability analysis on periodic tasks to polynomial time, and preliminary simulation results show that it also achieves an aperiodic responsiveness speedup of 4.1X-6.5X compared with existing work.

Safety-critical systems have suffered a complexity growth as the number of services continuously increases in these systems. The Logical Execution Time (LET) model is applied to tackle this issue due to its simple strategies and deterministic timed behaviors. However, existing implementations of LET usually rely on periodic timer interrupts of operating systems, yielding limited time precision and enormous jitter in kernel's executions. In this paper, we propose a time-triggered instruction set - TTI to augment ISA with timing properties. TTI implements as a processor architecture extension using co-processor2 interfaces in standard MIPS32. The extension mainly comprises a task management module, and a timed I/O-behaviors management module. Preliminary results show that our approach can significantly reduce overheads of LET kernel and jitters of the LET-based tasks compared to traditional implementations, which can achieve cycle-level precise timed behaviors as a result.