High-Level Synthesis for Reduction of WCET in Real-Time Systems

The increasing design complexity of systems-on-chip (SoCs) requires designers to work at higher levels of abstraction. High-level synthesis (HLS) is one approach towards this. It allows designers to synthesize hardware directly from code written in a high-level programming language and to more quickly explore alternative implementations by re-running the synthesis with different optimization parameters and pragmas. HLS is particularly interesting for FPGA circuits, where different hardware implementations can easily be loaded into the target device. Another perspective on HLS is performance. Compared to executing the high-level language code on a processor, HLS can be used to create hardware that accelerates critical parts of the code. When discussing performance in the context or real-time systems, it is the worst-case execution time (WCET) of a task that matters. WCET obviously benefits from hardware acceleration, but it may also benefit from a tighter bound on the WCET. This paper explores the use of and integration of accelerators generated using HLS into a time-predictable processor intended for real-time systems. The high-level design tool, Vivado HLS, is used to generate hardware accelerators from benchmark code, and the system using the generated hardware accelerators is evaluated against the WCET of the original code. The design evaluation is carried out using the Patmos processor from the open-source T-CREST platform and implemented on a Xilinx Artix 7 FPGA. The WCET speed-up achieved is between a factor of 5 and 70.