Tomasz S. Czajkowski

LegUp: high-level synthesis for FPGA-based processor/accelerator systems

In this paper, we introduce a new open source high-level synthesis tool called LegUp that allows software techniques to be used for hardware design. LegUp accepts a standard C program as input and automatically compiles the program to a hybrid architecture containing an FPGA-based MIPS soft processor and custom hardware accelerators that communicate through a standard bus interface. Results show that the tool produces hardware solutions of comparable quality to a commercial high-level synthesis tool.

LegUp: An open-source high-level synthesis tool for FPGA-based processor/accelerator systems

It is generally accepted that a custom hardware implementation of a set of computations will provide superior speed and energy efficiency relative to a software implementation. However, the cost and difficulty of hardware design is often prohibitive, and consequently, a software approach is used for most applications. In this article, we introduce a new high-level synthesis tool called LegUp that allows software techniques to be used for hardware design. LegUp accepts a standard C program as input and automatically compiles the program to a hybrid architecture containing an FPGA-based MIPS soft processor and custom hardware accelerators that communicate through a standard bus interface. In the hybrid processor/accelerator architecture, program segments that are unsuitable for hardware implementation can execute in software on the processor. LegUp can synthesize most of the C language to hardware, including fixed-sized multidimensional arrays, structs, global variables, and pointer arithmetic. Results show that the tool produces hardware solutions of comparable quality to a commercial high-level synthesis tool. We also give results demonstrating the ability of the tool to explore the hardware/software codesign space by varying the amount of a program that runs in software versus hardware. LegUp, along with a set of benchmark C programs, is open source and freely downloadable, providing a powerful platform that can be leveraged for new research on a wide range of high-level synthesis topics.

From opencl to high-performance hardware on FPGAS

We present an OpenCL compilation framework to generate high-performance hardware for FPGAs. For an OpenCL application comprising a host program and a set of kernels, it compiles the host program, generates Verilog HDL for each kernel, compiles the circuit using Altera Complete Design Suite 12.0, and downloads the compiled design onto an FPGA.We can then run the application by executing the host program on a Windows(tm)-based machine, which communicates with kernels on an FPGA using a PCIe interface. We implement four applications on an Altera Stratix IV and present the throughput and area results for each application. We show that we can achieve a clock frequency in excess of 160MHz on our benchmarks, and that OpenCL computing paradigm is a viable design entry method for high-performance computing applications on FPGAs.

Impact of FPGA architecture on resource sharing in high-level synthesis

Resource sharing is a key area-reduction approach in high-level synthesis (HLS) in which a single hardware functional unit is used to implement multiple operations in the high-level circuit specification. We show that the utility of sharing depends on the underlying FPGA logic element architecture and that different sharing trade-offs exist when 4-LUTs vs. 6-LUTs are used. We further show that certain multi-operator patterns occur multiple times in programs, creating additional opportunities for sharing larger composite functional units comprised of patterns of interconnected operators. A sharing cost/benefit analysis is used to inform decisions made in the binding phase of an HLS tool, whose RTL output is targeted to Altera commercial FPGA families: Stratix IV (dual-output 6-LUTs) and Cyclone II (4-LUTs).

High-Level Design Tools for Floating Point FPGAs

This tutorial describes tools for efficiently implementing floating point applications on FPGAs. We present both the SDK for OpenCL and DSP Builder Advanced Blockset and show that they can be effectively used to implement many floating point applications. The methods for optimizing application performance are also described. In this tutorial we focus on a few applications, including Fast Fourier transform, matrix multiplication, finite impulse response filter and a Cholesky decomposition. In all cases we show what the tools are capable of achieving, and more importantly how a user can take advantage of the various floating-point centric features that are made available. We also discuss how these tools can automatically use FPGA architectural features such as hardened floating-point DSP available on Altera Arria 10 family.

Silicon Verification using High-Level Design Tools (Abstract Only)

Modern FPGAs comprise ever more complex blocks to enable a wide variety of customer applications. Verification of the complex blocks can be a time consuming process, especially at the late stages of the release cycle. A key challenge is the time it takes to create circuits that can run on a target device to test a given block. This paper demonstrates how High-Level Design tools, such as Altera SDK for OpenCL, can be utilized to aid in this work to verify the operation of complex hardened blocks. As a proof of concept, we present the methodology used to verify the correctness of hardened single-precision floating point adder, subtractor and multiplier units on Altera Arria 10 FPGA in a single day. Each design comprised an instance of a hardened floating point unit, either an adder, subtractor or a multiplier, and a functional equivalent there of implemented purely using Lookup Tables (LUTs). Both the hardened module instance and the LUT implementation were generated from OpenCL description using Altera SDK for OpenCL. The results for each computation were compared between the two implementations and any single discrepancy constituted a test failure. To simplify the test, the I/O for each design comprised LEDs (for pass/fail/running/done status) and two switches -- start and reset. The test design for adder, subtractor and a multiplier were all written in OpenCL, the compilation of each design took approximately 30 minutes for each test design. Each design tested 4 billion test vectors, generated on-chip using a Mersenne Twister, and each test completed within 30 seconds. All tests passed verification in hardware.