Work-in-Progress: TTI: A Timing ISA for LET Model in Safety-Critical Systems

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.