Modern Processor Architectures Make WCET Analysis for HUME Challenging Christian Ferdinand AbsInt Angewandte Informatik GmbH

The Timing Problem P r o b a b i l i t y Execution Time Best Case Execution Time Exact Worst Case Execution Time

End-to-end Measurements P r o b a b i l i t y Execution Time Best Case Execution Time Exact Worst Case Execution Time Measured Worst-case Unsafe: Execution Time Measurement

Hybrid Approachs P r o b a b i l i t y Execution Time Best Case Execution Time Exact Worst Case Execution Time Combination of Local Measurements

Static Timing Analysis (Abstract Interpretation) P r o b a b i l i t y Execution Time Best Case Execution Time Exact Worst Case Execution Time SafeWorst Case Execution Time Estimate

EmBounded Low-Level Timing Analysis for Renesas M32C85  High-level source code: Hume … … is translated to HAM code (Hume Abstract Machine)  HAM code is translated to C  Each HAM instruction becomes a snippet of C code  C code is translated to M32C binary code  Each HAM instruction then becomes a snippet of M32C code  Use AbsInt’s aiT to analyze the M32C code corresponding to the HAM instructions

aiT vs. Measurement  Good precision in general  Note for MatchRule: Measurement error up to 3 cycles  See IFL06 paper Armelle Bonenfant et al., Worst-Case Execution Times for a Purely Functional Language

aiT WCET Analyzer Structure Interprocedural PAG-generated analyzers based on AI

Contexts with Loops INTERPROC: VIVU INTERPROC_L: 3

e300  e300 / PPC603e  MHz  Double precision FPU  Caches (LRU) + store buffer  Superscalar pipeline with out- of-order execution  Branch prediction (static)  Available in various processors, e.g. Freescale MPC82xx

Recursive C-Program Example

Conclusion  On M32-class processors  Current WCET analysis for Hume works well  On e300-class processors  Current WCET analysis for Hume will largely overestimate