High-level synthesis

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. First generation behavioral synthesis was introduced by Synopsys in 1994 as Behavioral Compiler 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. Forte Design Systems introduced its Cynthesizer tool which used SystemC as an entry language instead of Verilog or VHDL. Cynthesizer was adopted by many Japanese companies in 2000 as Japan had a very mature SystemC user community. The first high-level synthesis tapeout was achieved in 2001 by Sony using Cynthesizer. Adoption in the United States started in earnest in 2008. In 2006, an efficient and scalable "SDC modulo scheduling" technique was developed on control and data flow graphs and was later extended to pipeline scheduling. This technique uses the integer linear programming formulation. But it shows that the underlying constraint matrix is totally unimodular (after approximating the resource constraints). Thus, the problem can be solved in polynomial time optimally using a linear programming solver in polynomial time. This work was inducted to the FPGA and Reconfigurable Computing Hall of Fame 2022. The SDC scheduling algorithm was implemented in the xPilot HLS system developed at UCLA, and later licensed to the AutoESL Design Technologies, a spin-off from UCLA. AutoESL was acquired by Xilinx (now part of AMD) in 2011, and the HLS tool developed by AutoESL became the base of Xilinx HLS solutions, Vivado HLS and Vitis HLS, widely used for FPGA designs. ==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 they 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. 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. • Lexical processing • Algorithm optimization • Control/Dataflow analysis • Library processing • Resource allocation • Scheduling • Functional unit binding • Register binding • Output processing • Input Rebundling ==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. ==Vendors==

Data reported on recent Survey • Dynamatic from EPFL/ETH Zurich • MATLAB HDL Coder from Mathworks • HLS-QSP from CircuitSutra Technologies • C-to-Silicon from Cadence Design Systems • Concurrent Acceleration from Concurrent EDA • Symphony C Compiler from Synopsys • QuickPlay from PLDA • PowerOpt from ChipVision • Cynthesizer from Forte Design Systems (now Stratus HLS from Cadence Design Systems) • Catapult C from Calypto Design Systems, part of Mentor Graphics as of 2015, September 16. In November 2016 Siemens announced plans to acquire Mentor Graphics, Mentor Graphics became styled as "Mentor, a Siemens Business". In January 2021, the legal merger of Mentor Graphics with Siemens was completed - merging into the Siemens Industry Software Inc legal entity. Mentor Graphics' name was changed to Siemens EDA, a division of Siemens Digital Industries Software. • PipelineC [https://github.com/JulianKemmerer/PipelineC • CyberWorkBench from NEC • Mega Hardware • C2R from CebaTech • CoDeveloper from Impulse Accelerated Technologies • HercuLeS by Nikolaos Kavvadias • Program In/Code Out (PICO) from Synfora, acquired by Synopsys in June 2010 • xPilot from University of California, Los Angeles • Vsyn from vsyn.ru • ngDesign from SynFlow ==See also==