The built-in timing and power analysis engines of VPR are based on analytical models :cite:`VBetz_Book_1999,JGoeders_FPT_2012`. Analytical model-based analysis can promise accuracy only on a limited number of circuit designs for which the model is valid. As the technology advancements create more opportunities on circuit designs and FPGA architectures, the analytical power model require to be updated to follow the new trends. However, without referring to simulation results, the analytical power models cannot prove their accuracy. SPICE simulators have the advantages of generality and accuracy over analytical models. For this reason, SPICE simulation results are often selected to check the accuracy of analytical models. Therefore, there is a strong need for a simulation-based power analysis approach for FPGAs, which can support general circuit designs.
FPGA-SPICE aims at generating SPICE netlists and testbenches for the FPGA architectures supported by VPR. The SPICE netlists and testbenches are generated according to the placement and routing results of VPR. As a result, SPICE simulator can be used to perform precise delay and power analysis. The SPICE simulation results are useful in three aspects: (1) it can provide accurate power analysis; (2) it helps to improve the accuracy of built-in analytical models; and moreover (3) it creates opportunities in developing novel analytical models.
SPICE modeling for FPGA architectures requires detailed transistor-level modeling for all the circuit elements within the considered FPGA architecture. However, current VPR architectural description language :cite:`JLuu_FPGA_2011` does not offer enough transistor-level parameters to model the most common circuit modules, such as multiplexers and LUTs. Therefore, we develop an extension on the VPR architectural description language to model the transistor-level circuit designs.
In this manual, we will introduce how to use FPGA-SPICE to conduct an accurate power analysis. First, we give an overview of the design flow of FPGA-SPICE-based tool suites. Then, we show the command-line options of FPGA-SPICE. Afterward, we introduce the extension of architectural language and the transistor-level design supports. Finally, we present how to simulate the generated SPICE netlists and testbenches.
In the appendix, we introduce the hierarchy of the generated SPICE netlists and testbenches, to help you customize the SPICE netlists. We also attach an example of an architecture XML file for your interest.
Driven by the strong need in data processing applications, Field Programmable Gate Arrays (FPGAs) are playing an ever-increasing role as programmable accelerators in modern
computing systems. To fully unlock processing capabilities for domain-specific applications, FPGA architectures have to be tailored for seamless cooperation with other computing resources. However, prototyping and bringing to production a customized FPGA is a costly and complex endeavor even for industrial vendors. OpenFPGA, an opensource framework, aims to rapid prototype of customizable FPGA architectures through a semi-custom design approach. We propose an XML-to-Prototype design flow, where the Verilog netlists of a full FPGA fabric can be autogenerated using an extension of the XML language from the VTR framework and then fed into a back-end flow to generate production-ready layouts.
EDA support is essential for end-users to implement designs on a customized FPGA. OpenFPGA provides a general-purpose bitstream generator FPGA-Bitstream for any architecture that can be described by VPR. As the native CAD tool for any customized FPGA that is produced by FPGA-Verilog, FPGA-Bitstream is ready to use once users finalize the XML-based architecture description file. This eliminates the huge engineering efforts spent on developing bitstream generator for customized FPGAs.
Using FPGA-Bitstream, users can launch (1) Verilog-to-Bitstream flow. This is the typical implementation flow for end-users; (2) Verilog-to-Verification flow. OpenFPGA can output Verilog testbenches with self-testing features to validate users' implemetations on their customized FPGA fabrics.
