AHRB: A high-performance time-composable AMBA AHB bus

Hard real-time systems are moving toward complex systems comprising chips with different IP components connected with standard buses. AMBA is one of the most used bus interfaces and has already been included in processors in the real-time domain. However, AMBA was not designed to provide time composable Worst Case Execution Time (WCET) estimates, which are desirable to reduce timing validation and verification costs. This paper analyzes and extends the AMBA Advanced High-performance Bus (AHB) specification to enable time-composable WCET estimates by design. Concretely, (1) we analyze in detail the AMBA AHB in the context of hard real-time systems proving that it fails to provide time composability; (2) we define a restricted subset of AMBA AHB features, named restricted AHB (resAHB), that allows deriving time-composable, yet not tight, WCET estimates; and (3) we define an extension of resAHB, named Advanced High-performance Real-time Bus (AHRB), that includes the timing constraints in the specification. This allows deriving time-composable and tight WCET estimates. Our results show that AHRB can provide 3.5x tighter estimates than resAHB on average for EEMBC benchmarks.