Shared hardware data structures for hard real-time systems
Proceedings of the tenth ACM international conference on Embedded software
Data cache organization for accurate timing analysis
Real-Time Systems
An instruction scratchpad memory allocation for the precision timed architecture
DATE '12 Proceedings of the Conference on Design, Automation and Test in Europe
Optimizing a combined WCET-WCEC problem in instruction fetching for real-time systems
Journal of Systems Architecture: the EUROMICRO Journal
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A combination of a scratchpad and scratchpad memory management unit (SMMU) has been proposed as a way to implement fast and time-predictable memory access operations in programs that use dynamic data structures.A memory access operation is time-predictable if its execution time is known or bounded -- this is important within a hard real-time task so that the worst-case execution time (WCET) can be determined. However, the requirement for time-predictability does not remove the conventional requirement for efficiency:operations must be serviced as quickly as possible under worst-case conditions.This paper studies the capabilities of the SMMU when applied to a number of benchmark programs. A new allocation algorithm is proposed to dynamically manage the scratchpad space. In many cases,the SMMU vastly reduces the number of accesses to dynamic data structures stored in external memory along the worst-case execution path (WCEP). Across all the benchmarks,an average of 47% of accesses are rerouted to scratchpad, with nearly100% for some programs. In previous scratchpad-based work, time-predictability could only be assured for these operations using external memory.The paper also examines situations in which the SMMU does not perform so well, and discusses how these could be addressed.