Commercial Synthesis Tools Research Articles

Design of reverse converters for the general RNS 3-moduli set {2k, 2n − 1, 2n + 1}

This paper presents a new design method of the reverse (residue-to-binary) converter for the flexible 3-moduli residue number system (RNS) set { 2^k, 2^n-1, 2^n+1 }, where k and n are a pair of arbitrary integers ge 2. The basic equation of the reverse converter is formulated in two alternative forms, each of which consists of two separate parts: one depending on input variables of the converter, and the other being a single constant. The constant can be either added inside the reverse converter or shifted out to the residue datapath channels, in most cases at no hardware cost or extra delay. From the set of basic functions, which are essentially different than those of the only two known general converters proposed for this moduli set, four versions of a converter can be designed for any pair of k and n. Experimental results obtained using the commercial 65-nm low-power design kit and industrial synthesis tools for all dynamic ranges from 8 to 40 bits suggest that, compared to the state-of-the-art designs, at least one version of the newly proposed converters is superior w.r.t. delay, power consumption, and area, for all dynamic ranges considered. The savings for the best versions (these with constants moved to the datapath channels) are up to 12.7% for the area and from 2.5% to 14% (5.8 % on average) for the delay, while the power consumption is reduced up to 23.2% (5.6% on average).

Asynchronous Circuit Principles and a Survey of Associated Design Tools

Planning and implementing a semiconductor integrated circuit is a highly complex process. Although physical limits seem to be approaching, it currently follows a growing evolutionary path. As deep submicron technologies evolve towards perhaps even sub-nano geometries, the design process complicates accordingly. Once subtle in higher geometry nodes, some effects become relevant or even dominant. Examples are effects that tamper the reliability of wires, such as crosstalk, or the adequate behaviour of gates, such as the increasing sensitivity to single event effects. Design techniques must thus also evolve, to provide a wide range of tools to deal with new effects during the integrated circuit design and test processes. This tutorial covers one set of design techniques that is often overlooked, but which can reveal themselves instrumental in dealing with the mentioned technology evolution, the use of clockless or asynchronous circuits. The tutorial is divided into three parts: first it introduces a metamodel for the digital circuit design process enabling to reason about distinct design styles; second, it covers the main principles of asynchronous circuit design, differentiating it from mainstream circuit design techniques such as conventional synchronous design; the third and last part presents a set of tools and systems that can be employed to effectively design asynchronous design, with emphasis on material that can be used to produce manufacturable circuits and systems, often associated to commercial integrated circuit synthesis, implementation and test tools and frameworks.

BAS: A BTI-based aging aware synthesis in FPGAs

Aging mechanisms in FPGA devices cause performance degradation and lead to lifetime reduction. Among multiple aging mechanisms, Biased-Temperature-Instability (BTI) aging mechanism is the dominant one. BTI decreases the Static-Noise-Margin (SNM) of SRAM cells leading to more Soft-Error-Rate (SER) and lower SRAMs’ stability in FPGAs. This paper proposes the BAS (BTI Aware Synthesis), a three-step post-synthesis and pre-place-and-route tool to reduce the impact of BTI in FPGA’s LUTs significantly using the Bit-Flipping and Boolean Matching techniques. BAS receives a standard EDIF format synthesis output file from a synthesis tool (e.g., C.edf) and finally creates two output EDIF files with the same functionality as the original input file (e.g., C1.edf and C2.edf), while all LUT SRAMs contents are mutually flipped. The two BTI-Aware-created EDIF synthesis files are periodically used for FPGA’s reconfiguration. Our experimental results demonstrates that BAS improves SNM and SER on average by 16.1% and 15.7% compared to previous state-of-the-art techniques, respectively. BAS has two main advantages over previous state-of-the-art techniques: (1) it is more flexible and applicable as an embedded tool within worldwide commercial synthesis tools, and (2) unlike the previous state-of-the-art techniques, it does not need the map and details of the FPGAs.

Hide and Seek: Seeking the (Un)-Hidden Key in Provably-Secure Logic Locking Techniques

Logic locking is a holistic countermeasure that protects an integrated circuit (IC) from hardware-focused threats such as piracy of design intellectual property and unauthorized overproduction throughout the globalized IC supply chain. Out of the several techniques proposed by the hardware security community, provably-secure logic locking (PSLL) has acquired a foothold due to its algorithmic and provable-security guarantees. However, the security of these techniques are regularly questioned by attackers that exploit the vulnerabilities arising from the underlying hardware implementation. Unfortunately, such attacks (i) are predominantly specific to locking technique and (ii) lack generality and scalability. This leads to a plethora of attacks and researchers, especially defenders, find it challenging to ascertain the security of newly developed PSLL techniques. Additionally, there is no public repository of locked circuits, which attackers, can use to benchmark (and compare) their developed attacks. Driven by these challenges, we aim to develop a generalized attack that can recover the secret key across a breadth of PSLL techniques. To that end, we first categorize the existing PSLL techniques into two generic categories. Then, we extract functional and structural properties depending on the underlying hardware construction of the PSLL techniques and develop two attacks based on the concepts of VLSI testing and Boolean transformations. We evaluate our attacks on 30, 000 locked circuits across 14 PSLL techniques, including nine unbroken techniques. Our attacks successfully recover the secret key (100% accuracy) for all the considered techniques. Further, our experimentation across different (i) technology libraries, (ii) commercial and academic synthesis tools, and (iii) logic optimization settings provide several interesting insights. For instance, our attacks can recover the secret key by <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">only</i> using the locked circuit when an academic synthesis tool is used. Additionally, designers can use our attacks as a verification tool to ascertain the lower-bound security achieved by hardware implementations. Finally, we shall release our artifacts (post-review), which could help foster the development of future attacks and defenses in PSLL domain.

Buffer Placement and Sizing for High-Performance Dataflow Circuits

Commercial high-level synthesis tools typically produce statically scheduled circuits. Yet, effective C-to-circuit conversion of arbitrary software applications calls for dataflow circuits, as they can handle efficiently variable latencies (e.g., caches), unpredictable memory dependencies, and irregular control flow. Dataflow circuits exhibit an unconventional property: registers (usually referred to as “buffers”) can be placed anywhere in the circuit without changing its semantics, in strong contrast to what happens in traditional datapaths. Yet, although functionally irrelevant, this placement has a significant impact on the circuit’s timing and throughput. In this work, we show how to strategically place buffers into a dataflow circuit to optimize its performance. Our approach extracts a set of choice-free critical loops from arbitrary dataflow circuits and relies on the theory of marked graphs to optimize the buffer placement and sizing. Our performance optimization model supports important high-level synthesis features such as pipelined computational units, units with variable latency and throughput, and if-conversion. We demonstrate the performance benefits of our approach on a set of dataflow circuits obtained from imperative code.

Exploring high-order adder compressors for power reduction in sum of absolute differences architectures for real-time UHD video encoding

The sum of absolute difference (SAD) calculation is one of the most computing-intensive operations in video encoders compatible with recent standards, such as high-efficiency video coding (HEVC). SAD hardware architectures employ an adder tree to accumulate the coefficients from the absolute difference between two video blocks. This paper employs high-order adder compressors (HOAC) structures into SAD hardware architectures to achieve ultra-high definition (UHD) encoding in real time, using block sizes compatible with HEVC. The proposed HOAC architectures are power-efficient and enable low-power SAD hardware accelerators. Our throughput analysis shows that the HOAC-based SAD hardware architecture is capable of encoding UHD 4K ( $$3840\times 2160$$ ) videos in real-time at 60 frames per second. The architectures were entirely designed as dedicated ASIC blocks and were synthesized to ST 65 nm CMOS standard cells. Synthesis results show that SAD architectures using 64-2, 32-2, 16-2 and 8-2 compressors built from 4-2 compressors are significantly more efficient in terms of circuit area and total power dissipation when compared with SAD architectures using conventional adders selected by a commercial logic synthesis tool.

Automatic Retiming of Two-Phase Latch-Based Resilient Circuits

Timing resilient design has shown significant promise in mitigating the excess margins associated with rare worst-case data and increased process, voltage, and temperature variations. However, resilient circuits need error detecting sequential logic (EDL) to detect timing errors which incur area and power overhead. This paper proposes two alternatives to reduce the overhead in two-phase latch-based resilient circuits. The first is a new resiliency-aware graph-based approach to solve the retiming problem. The second uses a virtual resynthesis library to enable commercial synthesis tools to recognize the EDL overhead and optimize total area during retiming. We compare both approaches to a commercially standard retiming approach, which ignores the resiliency overheads, on a wide variety of benchmarks. Our experimental results show that our methods are computationally efficient and reduce the total circuit area by an average of up to 10%–15% when compared to traditional retiming.

Design Methodology to Explore Hybrid Approximate Adders for Energy-Efficient Image and Video Processing Accelerators

This paper proposes a new design methodology to explore the state-of-the-art approximate adders for accelerator architectures conceived in the realm of multiplier-less multiple constant multiplication optimization problem. The proposed methodology is composed of: 1) a search heuristic to seek faster and feasible approximate configurations for the architectures under evaluation; 2) low-power techniques regarding hybrid approximate adders design for accelerators based on trees of shift-and-add operations; 3) high-performance evaluation by exploring parallel prefix adders and low power analysis through the use of the adder optimized by a commercial synthesis tool in the precise part of the approximate adders; and 4) energy efficiency analysis by considering both the approximate techniques and voltage over scaling estimation. Furthermore, improvements are proposed for the state-of-the-art approximate adders under evaluation in this paper. Two case studies are considered to assess the proposed methodology: 1) Gaussian image filter and 2) Sobel operator. The precise and approximate image filters were described in very high-speed integrated circuits hardware description language regarding the proposed methodology. Results are shown after synthesis to a 45-nm standard cell-based technology, where energy reductions ranging from 7.7% up to 73.2% were experienced for multiple levels of quality considering the applications under analysis.

SLECTS: Slew-Driven Clock Tree Synthesis

A slew-driven clock tree synthesis (SLECTS) methodology is proposed for nanoscale technologies where the interconnect resistance dominates device resistance, thereby increasing the challenge of satisfying the slew constraint. This issue is exacerbated at lower voltages due to degraded drive ability of the clock buffers. A paradigm shift from the traditional delay (and skew)-driven approaches to the proposed slew-driven methodology is therefore required. SLECTS is developed in this paper to satisfy tight slew constraints, which can be costly or infeasible with delay (skew)-driven methodologies and reduce the power dissipation of the clock tree, since the slew and skew constraints are simultaneously and methodically considered. Experimental results performed on an industrial circuit with more than 1M gates designed in 28-nm technology demonstrate that clock power is reduced by approximately 15% as compared to a commercial clock tree synthesis tool under similar slew and skew constraints.

Optimal Generalized H-Tree Topology and Buffering for High-Performance and Low-Power Clock Distribution

Clock power, skew and maximum latency are three key metrics for clock distribution in low-power and high-performance designs. An H-tree offers minimum clock skew and good robustness against variations, but at the cost of large wirelength and clock power. On the other hand, a “fishbone” clock network with spine-ribs structures has smaller wirelength, latency and clock power, but larger skew, as compared to an H-tree. No previous work enables systematic exploration of the regime between H-tree and spine to achieve an optimal tradeoff among clock power, skew, and latency. In this paper, we study the concept of a generalized H-tree (GH-tree)—a topologically balanced tree with an arbitrary sequence of branching factors—and propose a dynamic programming-based method to determine optimal clock power, skew, and latency, in the space of GH-tree solutions. Our method co-optimizes clock tree topology and buffering along branches according to fitted electrical models. We further propose a balanced ${K}$ -means clustering and a linear programming (LP)-guided buffer placement approach to embed the GH-tree with respect to a given sink placement. We validate our solutions in commercial clock tree synthesis (CTS) tool flows, in a commercial foundry’s 28LP technology. The results show up to 30% clock power reduction while achieving similar skew and maximum latency as CTS solutions from recent versions of leading commercial place-and-route tools. Our proposed approach also achieves up to 56% clock power reduction while achieving similar skew and maximum latency as compared to CTS solutions from a state-of-the-art academic tool.

QDI Constant-Time Counters

Counters are a generally useful circuit that appear in many contexts. Because of this, the design space for clocked counters has been widely explored. However, the same cannot be said for robust clockless counters. To resolve this, we designed an array of constant response time counters using the most robust clockless logic family, quasi-delay-insensitive (QDI) circuits. We compare our designs to their closest QDI counterparts from the literature, showing significant improvements in design quality metrics including transistor count, energy per operation, frequency, and latency in a 28-nm process. We also compare our designs against prototypical synchronous counters generated by commercial logic synthesis tools.

FPGA design space exploration for scientific HPC applications using a fast and accurate cost model based on roofline analysis

High-performance computing on heterogeneous platforms in general and those with FPGAs in particular presents a significant programming challenge. We contend that compiler technology has to evolve to automatically optimize applications by transforming a given original program. We are developing a novel methodology based on type transformations on a functional description of a given scientific kernel, for generating correct-by-construction design variants. An associated lightweight costing mechanism for evaluating these variants is a cornerstone of our methodology, and the focus of this paper. We discuss our use of the roofline model to work with our optimizing compiler to enable us to quickly derive accurate estimates of performance from the design’s representation in our custom intermediate language. We show results confirming the accuracy of our cost model by validating it on different scientific kernels. A case study is presented to demonstrate that a solution created from our optimizing framework outperforms commercial high-level synthesis tools both in terms of throughput and power efficiency.

Fine-Grained Interconnect Synthesis

One of the key challenges for the FPGA industry going forward is to make the task of designing hardware easier. A significant portion of that design task is the creation of the interconnect pathways between functional structures. We present a synthesis tool that automates this process and focuses on the interconnect needs in the fine-grained (sub-IP-block) design space. Here there are several issues that prior research and tools do not address well: the need to have fixed, deterministic latency between communicating units (to enable high-performance local communication without the area overheads of latency insensitivity), and the ability to avoid generating unnecessary arbitration hardware when the application design can avoid it. Using a design example, our tool generates interconnect that requires 69% fewer lines of specification code than a handwritten Verilog implementation, which is a 32% overall reduction for the entire application. The resulting system, while requiring 6% more total functional and interconnect area, achieves the same performance. We also show a quantitative and qualitative advantages against an existing commercial interconnect synthesis tool, over which we achieve a 25% performance advantage and 15%/57% logic/memory area savings.

Automatic generation of efficient accelerators for reconfigurable hardware

Acceleration in the form of customized datapaths offer large performance and energy improvements over general purpose processors. Reconfigurable fabrics such as FPGAs are gaining popularity for use in implementing application-specific accelerators, thereby increasing the importance of having good high-level FPGA design tools. However, current tools for targeting FPGAs offer inadequate support for high-level programming, resource estimation, and rapid and automatic design space exploration. We describe a design framework that addresses these challenges. We introduce a new representation of hardware using parameterized templates that captures locality and parallelism information at multiple levels of nesting. This representation is designed to be automatically generated from high-level languages based on parallel patterns. We describe a hybrid area estimation technique which uses template-level models and design-level artificial neural networks to account for effects from hardware place-and-route tools, including routing overheads, register and block RAM duplication, and LUT packing. Our runtime estimation accounts for off-chip memory accesses. We use our estimation capabilities to rapidly explore a large space of designs across tile sizes, parallelization factors, and optional coarse-grained pipelining, all at multiple loop levels. We show that estimates average 4.8% error for logic resources, 6.1% error for runtimes, and are 279 to 6533 times faster than a commercial high-level synthesis tool. We compare the best-performing designs to optimized CPU code running on a server-grade 6 core processor and show speedups of up to 16.7×.

An evaluation and acceptance of COTS software for FPGA-based controllers in NPPS

FPGA (Field-Programmable Gate Array) has received much attention from nuclear industry as an alternative platform of PLC (Programmable Logic Controller)-based digital I&C (Instrumentation & Control). Software aspect of FPGA development encompasses several commercial tools such as logic synthesis and P&R (Place & Route), which should be first dedicated in accordance with domestic standards based on EPRI NP-5652. Even if a state-of-the-art supplementary EPRI TR-1025243 makes an effort, the dedication of indirect COTS (Commercial Off-The-Shelf) SW such as FPGA logic synthesis tools has still caused a dispute. This paper proposes an acceptance process and evaluation criteria, specific to COTS SW, not commercial-grade direct items. It specifically incorporates indirect COTS SW and also provides categorized evaluation criteria for acceptance. It provides an explicit linkage between acceptance methods (Verification and Validation techniques) and evaluation criteria, too. We tried to perform the evaluation and acceptance process upon a commercial FPGA logic synthesis tool being used to develop a new FPGA-based digital I&C in Korea, and could confirm its applicability.

Efficient Hardware Design of Iterative Stencil Loops

A large number of algorithms for multidimensional signals processing and scientific computation come in the form of iterative stencil loops (ISLs), whose data dependencies span across multiple iterations. Because of their complex inner structure, automatic hardware acceleration of such algorithms is traditionally considered as a difficult task. In this paper, we introduce an automatic design flow that identifies, in a wide family of bidimensional data processing algorithms, subportions that exhibit a kind of parallelism close to that of ISLs; these are mapped onto a space of highly optimized ad-hoc architectures, which is efficiently explored to identify the best implementations with respect to both area and throughput. Experimental results show that the proposed methodology generates circuits whose performance is comparable to that of manually optimized solutions, and orders of magnitude higher than those generated by commercial high-level synthesis tools.

Are HLS Tools Healthy? The C-Cubed Project

The increasing complexity of Application Specific Integrated Circuits (ASICs) and Systems-on-Chip (SoCs) that incorporate custom and standard embedded core IP blocks dictates the need for a new generation of automated and formal system EDA tools and methodologies. High-Level Synthesis (HLS) plays a critical role in the required Electronic System Level (ESL) methodologies. However, most of the available academic and commercial High-Level Synthesis (HLS) tools still do not play an established role in the system and hardware engineering teams. This is true for a number of practical reasons, analyzed and discussed in this work. The present article is a practical perspective of the required fully automated and formal tools, which are needed to constitute integral parts in Electronic Design Automation (EDA) flows. In addition, this article is a useful guide to the system engineer who wants to familiarize with HLS tools and to select the appropriate tool for the everyday engineering practice. The advanced HLS toolset that is analyzed in this paper is developed by the first author, its C-frontend by the second author, and they are both based on formal methods and fully automated techniques, thus they guarantee the correctness of the synthesized hardware implementations. This paper completes with a number of experiments that were executed using the author’s methodology and they are used to evaluate the specific HLS tools. Consequently, a number of conclusions are drawn as well as suggestions for the future directions of HLS technology. In this way, what is practically needed by the hardware systems engineering community is outlined at the end of the paper.

A Circuit Synthesis Flow for Controllable-Polarity Transistors

Double-gate (DG) controllable-polarity field-effect transistors (FETs) are devices whose n - or p - polarity is online configurable by adjusting the second gate voltage. Such emerging transistors have been fabricated in silicon nanowires, carbon nanotubes, and graphene technologies. Thanks to their enhanced functionality, DG controllable-polarity FETs implement arithmetic functions, such as XOR and MAJ, with limited physical resources enabling compact and high-performance datapaths. In order to design digital circuits with this technology, automated design techniques are of paramount importance. In this paper, we describe a design automation framework for DG controllable-polarity transistors. First, we present a novel dedicated logic representation form capable to exploit the polarity control during logic synthesis. Then, we tackle challenges at the physical level, presenting a regular layout technique that alleviates the interconnection issue deriving from the second gate routing. We use logic and physical synthesis tools to form a complete design automation flow. Experimental results show that the proposed flow is able to reduce the area and delay of digital circuits, based on 22-nm DG controllable-polarity Silicon nanowire (SiNW) FETs, by 22% and 42%, respectively, as compared to a commercial synthesis tool. With respect to a 22-nm FinFET technology, the proposed flow produces circuits, based on 22-nm DG controllable-polarity SiNWFETs, with 2.9 $\times$ smaller area-delay product.

On the development of high-throughput and area-efficient multi-mode cryptographic hash designs in FPGAs

In this paper, area-efficient and high-throughput multi-mode architectures for the SHA-1 and SHA-2 hash families are proposed and implemented in several FPGA technologies. Additionally a systematic flow for designing multi-mode architectures (implementing more than one function) of these families is introduced. Compared to the corresponding architectures that are produced by a commercial synthesis tool, the proposed ones are better in terms of both area (at least 40%) and throughput/area (from 32% up to 175%). Finally, the proposed architectures outperform similar existing ones in terms of throughput and throughput/area, from 4.2× up to 279.4× and from 1.2× up to 5.5×, respectively.

Exploiting Task- and Data-Level Parallelism in Streaming Applications Implemented in FPGAs

This article describes the design and implementation of a novel compilation flow that implements circuits in FPGAs from a streaming programming language. The streaming language supported is called FPGA Brook and is based on the existing Brook language. It allows system designers to express applications in a way that exposes parallelism, which can be exploited through hardware implementation. FPGA Brook supports replication, allowing parts of an application to be implemented as multiple hardware units operating in parallel. Hardware units are interconnected through FIFO buffers which use the small memory modules available in FPGAs. The FPGA Brook automated design flow uses a source-to-source compiler, developed as a part of this work, and combines it with a commercial behavioral synthesis tool to generate the hardware implementation. A suite of benchmark applications was developed in FPGA Brook and implemented using our design flow. Experimental results indicate that performance of many applications scales well with replication. Our benchmark applications also achieve significantly better results than corresponding implementations using a commercial behavioral synthesis tool. We conclude that using an automated design flow for implementation of streaming applications in FPGAs is a promising methodology.