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README.md

VeriScala

Introduction


Field Programmable Gate Arrays (FPGAs) have gained momentum in the past decade, when the improvements of high end CPUs started to level-off in terms of clock frequencies. Since FPGAs can provide more flexible and more efficient solutions in most occasions, manufacturers gradually adopt FPGA chips in their products such as CPUs and mobile devices. In the foreseeing future, FPGAs will be accessible computing resources and software developers will build applications interacting with FPGAs. However, the efficiency of development for applications based on FPGAs is severely constrained by the traditional languages and tools, due to their deficiency in expressibility, extendability, limited libraries and semantic gap between software and hardware descriptions. This project proposes a new open-source Domain-Specific Language (DSL) based framework called VeriScala that supports highly abstracted object-oriented hardware defining, programmatical testing, and interactive on-chip debugging. By adopting DSL embedded in Scala, we introduce modern software developing concepts into hardware designing including object-oriented programming, parameterized types, type safety, test automation, etc. VeriScala enables designers to describe their hardware designs in Scala, generate Verilog code automatically and debug and test hardware design interactively in real FPGA environment.

Detailed explanation is in the paper

File Organization


This GitHub project provides implementation of the VeriScala DSL. We build the project using SBT, and any IDE with scala and SBT supports can easily load it (Intellij IDEA is recommanded).

There are mainly two directory in the project

  • examples
  • newhdl

examples gives the demo implementation and corresponding test in VeriScala DSL

newhdl provides the core implementation of the DSL

VeriScala/newhdl/src/main/scala/ holds

  • Core
  • Exceptions
  • Simulation

The relation amomg the files in these three directories is show in the figure below

VeriScala/examples/src/main/ gives part of the demo implementations

VeriScala/examples/src/test/scala/ gives software test bench of the demo implementations

VeriScala/examples/compile_result/ gives generation results of the demo implementations

Usability Test


The test is conducted on ten experienced high-level language programmers with close age and years of programming career. The test includes the following steps:

  • Divide ten people into two groups. One is called VeriScala group, and the other Verilog group.
  • Read the prepared specification booklet of VeriScala or Verilog corresponding to their groups, implement a FlashLED module after reading, and record the total time costed.
  • Swap the group, and do the jobs in last step again.
  • Count the code lines of each implementation and check the correctness.
  • Analyse the collected data.

Without or with little modification on syntax, every piece of code passes our test, which indicates that people find no trouble in using VeriScala to describe correct hardware design, and VeriScala is effective to learn. From the data, we firstly find that nearly every one use less code to do the job when using VeriScala, which can be seen in the figure below.

This result is different from the result shown in V-B1 where code lines of VeriScala will be a little more than that of Verilog. By reading the code, we find that people do not always use the same logic to implement the FlashLED, they will change their designs according to language features, such as high-order functions in Scala, which will obviously decrease the code lines.

Another discovery is that, shown in the figure above, the total implementation time tends to be shorter, if they first learn VeriScala other than Verilog. Interviews indicate the reason, which is that Verilog is hard for beginners and VeriScala serves as a good warm-up. Final discovery is demonstrated by Figure 9. This figure shows that Scala programmer will have advantages in learning VeriScala for they use less time both in total and VeriScala, which is a reasonable result.

Applications


MIPS CPU

VeriScala/examples/src/main/scala/Mips/

For a real world application, we implement a full feature system, a five-stage single cycle CPU supporting MIPS instruction set. To validate the generated code, we run the same test bench for both variants on Modelsim, and additionally we build support to I/O with FPGA board along with a simple subtractor based on it to see if the system runs well on real hardware. This substractor is implemented by MIPS assembly code and interacts via the on-board interface, where switches are used to control each bit of input data and the 7-segment displays show the operators and result. It turns out that the automatically generated CPU works well both on simulator and hardware, for it has the same behavior as the manually written one.

Video Transcoder

VeriScala/examples/src/main/scala/Camera/

The Verilog design of the video transcoder is an example from the CD that comes along with the SoC-DE1 board. We implement the VeriScala variant based on this code. However, many encrypted IP cores are introduced and there is no corresponding implementation in current VeriScala libraries, which results in that we have to manually write some module instantiation statement in generated code. Figure below demonstrates how this system looks like. It uses a TRDB-D5M camera to capture raw data, then after transcoding and buffering, it displays the pictures via a VGA bus on the screen.