WCET Centric Data Allocation to Scratchpad Memory

Scratchpad memory is a popular choice for on-chip storage in real-time embedded systems. The allocation of code/data to scratchpad memory is performed at compile time leading to predictable memory access latencies. Current scratchpad memory allocation techniques improve the average-case execution time of tasks. For hard real-time systems, on the other hand, worst case execution time (WCET) is a key metric. In this paper, we propose scratchpad allocation techniques for data memory that aim to minimize a task's WCET. We first develop an integer linear programming (ILP) based solution which constructs the optimal allocation assuming that all program paths are feasible. Next, we employ branch-and-bound search to more accurately construct the optimal allocation by exploiting infeasible path information. However, the branch-and-bound search is too time-consuming in practice. Therefore, we design fast heuristic searches that achieve near-optimal allocations for all our benchmarks.