High-level synthesis

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High-level synthesis (HLS), sometimes referred to as C synthesis, electronic system-level (ESL) synthesis, algorithmic synthesis, or behavioral synthesis, is an automated design process that interprets an algorithmic description of a desired behavior and creates digital hardware that implements that behavior. [1] Synthesis begins with a high-level specification of the problem, where behavior is generally decoupled from e.g. clock-level timing. Early HLS explored a variety of input specification languages., [2] although recent research and commercial applications generally accept synthesizable subsets of ANSI C/C++/SystemC/MATLAB. The code is analyzed, architecturally constrained, and scheduled to transcompile into a register-transfer level (RTL) design in a hardware description language (HDL), which is in turn commonly synthesized to the gate level by the use of a logic synthesis tool. The goal of HLS is to let hardware designers efficiently build and verify hardware, by giving them better control over optimization of their design architecture, and through the nature of allowing the designer to describe the design at a higher level of abstraction while the tool does the RTL implementation. Verification of the RTL is an important part of the process. [3]

In electronics and especially synchronous digital circuits, a clock signal is a particular type of signal that oscillates between a high and a low state and is used like a metronome to coordinate actions of digital circuits.

ANSI C, ISO C and Standard C refer to the successive standards for the C programming language published by the American National Standards Institute (ANSI) and the International Organization for Standardization (ISO). Historically, the names referred specifically to the original and best-supported version of the standard. Software developers writing in C are encouraged to conform to the standards, as doing so helps portability between compilers.

C++ General-purpose programming language

C++ is a general-purpose programming language created by Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significantly over time, and modern C++ has object-oriented, generic, and functional features in addition to facilities for low-level memory manipulation. It is almost always implemented as a compiled language, and many vendors provide C++ compilers, including the Free Software Foundation, LLVM, Microsoft, Intel, and IBM, so it is available on many platforms.

Contents

Hardware can be designed at varying levels of abstraction. The commonly used levels of abstraction are gate level, register-transfer level (RTL), and algorithmic level.

Digital electronics Electronic circuits that utilize digital signals

Digital electronics, digital technology or digital (electronic) circuits are electronics that operate on digital signals. In contrast, analog circuits manipulate analog signals whose performance is more subject to manufacturing tolerance, signal attenuation and noise. Digital techniques are helpful because it is a lot easier to get an electronic device to switch into one of a number of known states than to accurately reproduce a continuous range of values.

In digital circuit design, register-transfer level (RTL) is a design abstraction which models a synchronous digital circuit in terms of the flow of digital signals (data) between hardware registers, and the logical operations performed on those signals.

Algorithm An unambiguous specification of how to solve a class of problems

In mathematics and computer science, an algorithm is a set of instructions, typically to solve a class of problems or perform a computation. Algorithms are unambiguous specifications for performing calculation, data processing, automated reasoning, and other tasks.

While logic synthesis uses an RTL description of the design, high-level synthesis works at a higher level of abstraction, starting with an algorithmic description in a high-level language such as SystemC and ANSI C/C++. The designer typically develops the module functionality and the interconnect protocol. The high-level synthesis tools handle the micro-architecture and transform untimed or partially timed functional code into fully timed RTL implementations, automatically creating cycle-by-cycle detail for hardware implementation. [4] The (RTL) implementations are then used directly in a conventional logic synthesis flow to create a gate-level implementation.

In electronics, logic synthesis is a process by which an abstract specification of desired circuit behavior, typically at register transfer level (RTL), is turned into a design implementation in terms of logic gates, typically by a computer program called a synthesis tool. Common examples of this process include synthesis of designs specified in hardware description languages, including VHDL and Verilog. Some synthesis tools generate bitstreams for programmable logic devices such as PALs or FPGAs, while others target the creation of ASICs. Logic synthesis is one aspect of electronic design automation.

History

Early academic work extracted scheduling, allocation, and binding as the basic steps for high-level-synthesis. Scheduling partitions the algorithm in control steps that are used to define the states in the finite-state machine. Each control step contains one small section of the algorithm that can be performed in a single clock cycle in the hardware. Allocation and binding maps the instructions and variables to the hardware components, multiplexers, registers and wires of the data path.

Finite-state machine Mathematical model of computation

A finite-state machine (FSM) or finite-state automaton, finite automaton, or simply a state machine, is a mathematical model of computation. It is an abstract machine that can be in exactly one of a finite number of states at any given time. The FSM can change from one state to another in response to some external inputs; the change from one state to another is called a transition. An FSM is defined by a list of its states, its initial state, and the conditions for each transition. Finite state machines are of two types – deterministic finite state machines and non-deterministic finite state machines. A deterministic finite-state machine can be constructed equivalent to any non-deterministic one.

First generation behavioral synthesis was introduced by Synopsys in 1994 as Behavioral Compiler [5] and used Verilog or VHDL as input languages. The abstraction level used was partially timed (clocked) processes. Tools based on behavioral Verilog or VHDL were not widely adopted in part because neither languages nor the partially timed abstraction were well suited to modeling behavior at a high level. 10 years later, in early 2004, Synopsys end-of-lifed Behavioral Compiler. [6]

Synopsys is an American EDA company. Majority of their products include tools used in the design of an application-specific integrated circuit. Products include logic synthesis, behavioral synthesis, place and route, static timing analysis, formal verification, hardware description language simulators as well as transistor-level circuit simulation. The simulators include development and debugging environments which assist in the design of the logic for chips and computer systems. In recent years Synopsys has also expanded into the application security market.

Verilog, standardized as IEEE 1364, is a hardware description language (HDL) used to model electronic systems. It is most commonly used in the design and verification of digital circuits at the register-transfer level of abstraction. It is also used in the verification of analog circuits and mixed-signal circuits, as well as in the design of genetic circuits. In 2009, the Verilog standard was merged into the SystemVerilog standard, creating IEEE Standard 1800-2009. Since then, Verilog is officially part of the SystemVerilog language. The current version is IEEE standard 1800-2017.

VHDL hardware description language

VHDL (VHSIC-HDL) is a hardware description language used in electronic design automation to describe digital and mixed-signal systems such as field-programmable gate arrays and integrated circuits. VHDL can also be used as a general purpose parallel programming language.

In 2004, there emerged a number of next generation commercial high-level synthesis products (also called behavioral synthesis or algorithmic synthesis at the time) which provided synthesis of circuits specified at C level to a register transfer level (RTL) specification. [7] Synthesizing from the popular C language offered accrued abstraction, expressive power and coding flexibility while tying with existing flows and legacy models. This language shift, combined with other technical advances was a key enabler for successful industrial usage. High-level synthesis tools are used for complex ASIC and FPGA design.

Application-specific integrated circuit Integrated circuit customized (typically optimized) for a specific task

An application-specific integrated circuit is an integrated circuit (IC) customized for a particular use, rather than intended for general-purpose use. For example, a chip designed to run in a digital voice recorder or a high-efficiency bitcoin miner is an ASIC. Application-specific standard products (ASSPs) are intermediate between ASICs and industry standard integrated circuits like the 7400 series or the 4000 series.

Field-programmable gate array array of logic gates that are reprogrammable

A field-programmable gate array (FPGA) is an integrated circuit designed to be configured by a customer or a designer after manufacturing – hence the term "field-programmable". The FPGA configuration is generally specified using a hardware description language (HDL), similar to that used for an Application-Specific Integrated Circuit (ASIC). Circuit diagrams were previously used to specify the configuration, but this is increasingly rare due to the advent of electronic design automation tools.

High-level synthesis was primarily adopted in Japan and Europe in the early years. As of late 2008, there was an emerging adoption in the United States. [8]

Source input

The most common source inputs for high-level synthesis are based on standard languages such as ANSI C/C++, SystemC and MATLAB.

High-level synthesis typically also includes a bit-accurate executable specification as input, since to derive an efficient hardware implementation, additional information is needed on what is an acceptable Mean-Square Error or Bit-Error Rate etc. For example, if the designer starts with an FIR filter written using the "double" floating type, before he or she can derive an efficient hardware implementation, they need to perform numerical refinement to arrive at a fixed-point implementation. The refinement requires additional information on the level of quantization noise that can be tolerated, the valid input ranges etc. This bit-accurate specification makes the high level synthesis source specification functionally complete. [9] Normally the tools infer from the high level code a Finite State Machine and a Datapath that implement arithmetic operations.

Process stages

The high-level synthesis process consists of a number of activities. Various high-level synthesis tools perform these activities in different orders using different algorithms. Some high-level synthesis tools combine some of these activities or perform them iteratively to converge on the desired solution. [10]

Functionality

In general, an algorithm can be performed over many clock cycles with few hardware resources, or over fewer clock cycles using a larger number of ALUs, registers and memories. Correspondingly, from one algorithmic description, a variety of hardware microarchitectures can be generated by an HLS compiler according to the directives given to the tool. This is the same trade off of execution speed for hardware complexity as seen when a given program is run on conventional processors of differing performance, yet all running at roughly the same clock frequency.

Architectural constraints

Synthesis constraints for the architecture can automatically be applied based on the design analysis. [3] These constraints can be broken into

Interface synthesis

Interface Synthesis refers to the ability to accept pure C/C++ description as its input, then use automated interface synthesis technology to control the timing and communications protocol on the design interface. This enables interface analysis and exploration of a full range of hardware interface options such as streaming, single- or dual-port RAM plus various handshaking mechanisms. With interface synthesis the designer does not embed interface protocols in the source description. Examples might be: direct connection, one line, 2 line handshake, FIFO. [11]

Vendors

Data reported on recent Survey [12]

StatusCompilerOwnerLicenseInputOutputYearDomainTest
Bench
FPFixP
In Use AUGH TIMA Lab.AcademicC subsetVHDL2012AllYesNoNo
eXCite Y ExplorationsCommercialCVHDL/Verilog2001AllYesNoYes
Bambu PoliMiAcademicCVHDL/Verilog2012AllYesYesNo
Bluespec BlueSpec Inc.CommercialBSVSystemVerilog2007AllNoNoNo
CHCAltiumCommercialC subsetVHDL/Verilog2008AllNoYesYes
CoDeveloperImpulse AcceleratedCommercialImpulse-CVHDL2003Image
Streaming
YesYesNo
StratusCadenceCommercialC/C++ SystemCRTL2015AllYesNoYes
CyberWorkbenchNECCommercialBDL, SystemCVHDL/Verilog2011AllCycle/
Formal
YesYes
CatapultMentor
(Siemens business)
CommercialC, C++, SystemCVHDL/Verilog2004StreamingNoNoYes
DWARVTU. DelftAcademicC subsetVHDL2012AllYesYesYes
GAUT U. BretagneAcademicC/C++VHDL2010DSPYesNoYes
Hastlayer Lombiq TechnologiesCommercialC#/C++/F#...
(.NET)
VHDL2015.NETYesYesYes
Intel High Level Synthesis Compiler Intel FPGA (Formerly Altera)CommercialC/C++Verilog2017AllYesYesYes
LegUp HLS LegUp ComputingCommercialCVerilog2017AllYesYesNo
LegUp U. TorontoAcademicCVerilog2011AllYesYesNo
MaxCompilerMaxelerCommercialMaxJRTL2010DataFlowNoYesNo
ROCCC Jacquard Comp.CommercialC subsetVHDL2010StreamingNoYesNo
Synphony CSynopsysCommercialC/C++VHDL/Verilog/
SystemC
2010AllYesNoYes
VivadoHLS
(formerly AutoPilot
from AutoESL [13] )
XilinxCommercialC/C++/SystemCVHDL/Verilog/
SystemC
2013AllYesYesYes
Kiwi U. CambridgeAcademicC#Verilog2008.NETNoYesYes
CHiMPSU. WashingtonAcademicCVHDL2008AllNoNoNo
gcc2verilogU. KoreaAcademicCVerilog2011AllNoNoNo
HercuLeSAjax CompilersCommercialC/NACVHDL2012AllYesYesYes
Shang ?U. IllinoisCVerilog2013AllYes??
TridentLos Alamos NLAcademicC subsetVHDL2007ScientificNoYesNo
Aban-
doned
AccelDSPXilinxCommercialMATLABVHDL/Verilog2006DSPYesYesYes
C2HAlteraCommercialCVHDL/Verilog2006AllNoNoNo
CtoVerilogU. HaifaAcademicCVerilog2008AllNoNoNo
DEFACTOU. South Cailf.AcademicCRTL1999DSENoNoNo
GarpU. BerkeleyAcademicC subsetbitstream2000LoopNoNoNo
MATCHU. NorthwestAcademicMATLABVHDL2000ImageNoNoNo
Napa-CSarnoff Corp.AcademicC subsetVHDL/Verilog1998LoopNoNoNo
PipeRenchU.Carnegie M.AcademicDILbistream2000StreamNoNoNo
SA-CU. ColoradoAcademicSA-CVHDL2003ImageNoNoNo
SeaCucumberU. Brigham Y.AcademicJavaEDIF2002AllNoYesYes
SPARKU. Cal. IrvineAcademicCVHDL2003ControlNoNoNo

See also

Related Research Articles

In computer engineering, a hardware description language (HDL) is a specialized computer language used to describe the structure and behavior of electronic circuits, and most commonly, digital logic circuits.

System on a chip type of integrated circuit

A system on a chip is an integrated circuit that integrates all components of a computer or other electronic system. These components typically include a central processing unit (CPU), memory, input/output ports and secondary storage – all on a single substrate or microchip, the size of a coin. It may contain digital, analog, mixed-signal, and often radio frequency signal processing functions, depending on the application. As they are integrated on a single substrate, SoCs consume much less power and take up much less area than multi-chip designs with equivalent functionality. Because of this, SoCs are very common in the mobile computing and edge computing markets. Systems on chip are commonly used in embedded systems and the Internet of Things.

Electronic design automation (EDA), also referred to as electronic computer-aided design (ECAD), is a category of software tools for designing electronic systems such as integrated circuits and printed circuit boards. The tools work together in a design flow that chip designers use to design and analyze entire semiconductor chips. Since a modern semiconductor chip can have billions of components, EDA tools are essential for their design.

Formal equivalence checking process is a part of electronic design automation (EDA), commonly used during the development of digital integrated circuits, to formally prove that two representations of a circuit design exhibit exactly the same behavior.

Integrated circuit design Engineering process for electronic hardware

Integrated circuit design, or IC design, is a subset of electronics engineering, encompassing the particular logic and circuit design techniques required to design integrated circuits, or ICs. ICs consist of miniaturized electronic components built into an electrical network on a monolithic semiconductor substrate by photolithography.

In electronic design automation, functional verification is the task of verifying that the logic design conforms to specification. In everyday terms, functional verification attempts to answer the question "Does this proposed design do what is intended?" This is a complex task, and takes the majority of time and effort in most large electronic system design projects. Functional verification is a part of more encompassing design verification, which, besides functional verification, considers non-functional aspects like timing, layout and power.

Hardware emulation Emulating hardware devices in IC design

In integrated circuit design, hardware emulation is the process of imitating the behavior of one or more pieces of hardware with another piece of hardware, typically a special purpose emulation system. The emulation model is usually based on a hardware description language source code, which is compiled into the format used by emulation system. The goal is normally debugging and functional verification of the system being designed. Often an emulator is fast enough to be plugged into a working target system in place of a yet-to-be-built chip, so the whole system can be debugged with live data. This is a specific case of in-circuit emulation.

Electronic system level (ESL) design and verification is an electronic design methodology, focused on higher abstraction level concerns. The term Electronic System Level or ESL Design was first defined by Gartner Dataquest, an EDA-industry-analysis firm, on February 1, 2001. It is defined in ESL Design and Verification as: "the utilization of appropriate abstractions in order to increase comprehension about a system, and to enhance the probability of a successful implementation of functionality in a cost-effective manner."

Jingsheng Jason Cong is a Chinese-born American computer scientist, educator, and serial entrepreneur. He received his B.S. degree in computer science from Peking University in 1985, his M.S. and Ph. D. degrees in computer science from the University of Illinois at Urbana-Champaign in 1987 and 1990, respectively. He has been on the faculty in the Computer Science Department at the University of California, Los Angeles (UCLA) since 1990. Currently, he is a Distinguished Chancellor’s Professor and the director of Center for Domain-Specific Computing (CDSC).

C to HDL tools convert C language or C-like computer code into a hardware description language (HDL) such as VHDL or Verilog. The converted code can then be synthesized and translated into a hardware device such as a field-programmable gate array. Compared to software, equivalent designs in hardware consume less power and execute faster with lower latency, more parallelism and higher throughput. However, system design and functional verification in a hardware description language can be tedious and time-consuming, so systems engineers often write critical modules in HDL and other modules in a high-level language and synthesize these into HDL through C to HDL or high-level synthesis tools.

Graphical system design (GSD) is a modern approach to designing measurement and control systems that integrates system design software with COTS hardware to dramatically simplify development. This approach combines user interfaces, models of computation, math and analysis, Input/output signals, technology abstractions, and various deployment target. It allows domain experts, or non- implementation experts, to access to design capabilities where they would traditionally need to outsource a system design expert.

Aldec, Inc. is a privately owned electronic design automation company based in Henderson, Nevada that provides software and hardware used in creation and verification of digital designs targeting FPGA and ASIC technologies.

Forte Design Systems, Inc. is a San Jose, CA, based provider of high-level synthesis (HLS) software products, also known as electronic system-level (ESL) synthesis. Forte's main product is Cynthesizer. On February 14, 2014, Forte was acquired by Cadence Design Systems. Terms of the transaction were not disclosed.

Verilator

Verilator is a free and open-source software tool which converts Verilog to a cycle-accurate behavioral model in C++ or SystemC. It is restricted to modeling the synthesizable subset of Verilog and the generated models are cycle-accurate, 2-state, with synthesis semantics. As a consequence, the models typically offer higher performance than the more widely used event-driven simulators, which can process the entire Verilog language and model behavior within the clock cycle. Verilator is now used within academic research, open source projects and for commercial semiconductor development. It is part of the growing body of free EDA software.

Catapult C Synthesis, a commercial electronic design automation product of Mentor Graphics, is a high-level synthesis tool, sometimes called algorithmic synthesis or ESL synthesis. Catapult C takes ANSI C/C++ and SystemC inputs and generates register transfer level (RTL) code targeted to FPGAs and ASICs.

High-level verification (HLV), or electronic system-level (ESL) verification, is the task to verify ESL designs at high abstraction level, i.e., it is the task to verify a model that represents hardware above register-transfer level (RTL) abstract level. For high-level synthesis, HLV is to HLS as functional verification is to logic synthesis.

EVE/ZeBu

EVE/ZeBu is a provider of hardware-assisted verification tools for functional verification of Application-specific integrated circuits (ASICs) and system on chip (SOC) designs and for validation of embedded software ahead of implementation in silicon. EVE's hardware acceleration and hardware emulation products work in conjunction with Verilog, SystemVerilog, and VHDL-based simulators from Synopsys, Cadence Design Systems and Mentor Graphics. EVE's flagship product is ZeBu.

Xilinx Vivado

Vivado Design Suite is a software suite produced by Xilinx for synthesis and analysis of HDL designs, superseding Xilinx ISE with additional features for system on a chip development and high-level synthesis. Vivado represents a ground-up rewrite and re-thinking of the entire design flow, and has been described by reviewers as "well conceived, tightly integrated, blazing fast, scalable, maintainable, and intuitive".

VisualSim Architect

VisualSim Architect is an electronic system-level software for modeling and simulation of electronic systems, embedded software and semiconductors. VisualSim Architect is a commercial version of the Ptolemy II research project at University of California Berkeley. The product was first released in 2003. VisualSim is a graphical tool that can be used for performance trade-off analyses using such metrics as bandwidth utilization, application response time and buffer requirements. It can be used for architectural analysis of algorithms, components, software instructions and hardware/ software partitioning.

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Further reading