EXTRA: Towards the exploitation of eXascale technology for reconfigurable architectures

© 2016 IEEE. To handle the stringent performance requirements of future exascale-class applications, High Performance Computing (HPC) systems need ultra-efficient heterogeneous compute nodes. To reduce power and increase performance, such compute nodes will require hardware accelerators with a high degree of specialization. Ideally, dynamic reconfiguration will be an intrinsic feature, so that specific HPC application features can be optimally accelerated, even if they regularly change over time. In the EXTRA project, we create a new and flexible exploration platform for developing reconfigurable architectures, design tools and HPC applications with run-time reconfiguration built-in as a core fundamental feature instead of an add-on. EXTRA covers the entire stack from architecture up to the application, focusing on the fundamental building blocks for run-time reconfigurable exascale HPC systems: new chip architectures with very low reconfiguration overhead, new tools that truly take reconfiguration as a central design concept, and applications that are tuned to maximally benefit from the proposed run-time reconfiguration techniques. Ultimately, this open platform will improve Europe's competitive advantage and leadership in the field

Trace-based automated logical debugging for high-level synthesis generated circuits

In this paper we present an approach for debugging hardware designs generated by High-Level Synthesis (HLS), relieving users from the burden of identifying the signals to trace and from the error-prone task of manually checking the traces. The necessary steps are performed after HLS, independently of it and without affecting the synthesized design. For this reason our methodology should be easily adaptable to any HLS tools. The proposed approach makes full use of HLS compile time informations. The executions of the simulated design and the original C program can be compared, checking if there are discrepancies between values of C variables and signals in the design. The detection is completely automated, that is, it does not need any input but the program itself and the user does not have to know anything about the overall compilation process. The design can be validated on a given set of test cases and the discrepancies are detected by the tool. Relationships between the original high-level source code and the generated HDL are kept by the compiler and shown to the user. The granularity of such discrepancy analysis is per-operation and it includes the temporary variables inserted by the compiler. As a consequence the design can be debugged as is, with no restrictions on optimizations available during HLS. We show how this methodology can be used to identify different kind of bugs: 1) introduced by the HLS tool used for the synthesis; 2) introduced using buggy libraries of hardware components for HLS; 3) undefined behavior bugs in the original high-level source code

Transparent In-Circuit Assertions for FPGAs

Commonly used in software design, assertions are statements placed into a design to ensure that its behaviour matches that expected by a designer. Although assertions apply equally to hardware design, they are typically supported only for logic simulation, and discarded prior to physical implementation. We propose a new HDL-agnostic language for describing latency-insensitive assertions and novel methods to add such assertions transparently to an already placed-and-routed circuit without affecting the existing design. We also describe how this language and associated methods can be used to implement semi-transparent exception handling. The key to our work is that by treating hardware assertions and exceptions as being oblivious or less sensitive to latency, assertion logic need only use spare FPGA resources. We use network-flow techniques to route necessary signals to assertions via spare flip-flops, eliminating any performance degradation, even on large designs (92% of slices in one test). Experimental evaluation shows zero impact on critical-path delay, even on large benchmarks operating above 200MHz, at the cost of a small power penalty

KAPow: high-accuracy, low-overhead online per-module power estimation for FPGA designs

In an FPGA system-on-chip design, it is often insufficient to merely assess the power consumption of the entire circuit by compile-time estimation or runtime power measurement. Instead, to make better decisions, one must understand the power consumed by each module in the system. In this work, we combine measurements of register-level switching activity and system-level power to build an adaptive online model that produces live breakdowns of power consumption within the design. Online model refinement avoids time-consuming characterisation while also allowing the model to track long-term operating condition changes. Central to our method is an automated flow that selects signals predicted to be indicative of high power consumption, instrumenting them for monitoring. We named this technique KAPow, for 'K'ounting Activity for Power estimation, which we show to be accurate and to have low overheads across a range of representative benchmarks. We also propose a strategy allowing for the identification and subsequent elimination of counters found to be of low significance at runtime, reducing algorithmic complexity without sacrificing significant accuracy. Finally, we demonstrate an application example in which a module-level power breakdown can be used to determine an efficient mapping of tasks to modules and reduce system-wide power consumption by up to 7%