I want to convert my lane detection code written by C++ (OpenCV) to FPGA. Vivado HLS or Vivado SDSoC can help to embed the C ++ code into the FPGA. Or I can rewrite the lane detection code with verilog. The question is, what are the advantages and disadvantages of these three ways? I want to use one of the cheap Zynq-7000 FPGAs.
5 Answers
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Verilog is considered low-level these days. Compare it with assembly for software implementation. People use it only to get performance that they cannot attain with high-level languages such as C or Java in the software domain.
In the hardware domain, C (for Vivado HLS) or OpenCL are considered high-level languages. OpenCL was developed with portability to other architectures like GPUs and CPUs in mind. It has a lot more overhead in terms of communicating with the FPGA than Vivado HLS however.
Vivado HLS by itself produces just hardware modules in VHDL or Verilog, which you still have to connect to FPGA pins, ARM processors, etc. It does not take care of the communication to your module. You will still have to integrate your module in a Vivado block design or top-level VHDL or Verilog implementation yourself.
SDSoC, not "Vivado SDSoC" by the way, also lets you to write your entire implementation (hardware and software) in C. Under the hood, it will invoke Vivado HLS to implement the hardware module. Afterwards, the tool will take care of implementing an interface between your hardware and the on-board ARM processors that will run the software.
In summary, I recommend SDSoC unless you have a good reason not to use it. I do want to warn, however, that analyzing the synthesis results of Vivado HLS is a lot harder than analyzing Vivado output for Verilog or VHDL. Therefore, I always recommend to make sure that your code works as a software implementation first. With minimal effort, you should be able to compile any code in gcc or another compiler too. Don't use the synthesis results to debug your code, but just to analyze the performance.
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Take a look at Xilinx XAPP1167 and the Xilinx HLS Video Library Wiki.
That appnote is a few years old (older than the SDSoC tools) but has a reference design for accelerating OpenCV applications in a Zynq using HLS.
I can't speak to SDSoC, but I would highly recommend starting with HLS over a rewrite in Verilog. It sounds like you have exactly an intended use-case for HLS: to implement existing C++ applications in an FPGA. The downsides to it are (1) you'll likely need to modify your code a bit, since HLS doesn't support all C++ features, and (2) the performance may not be quite as good as a pure Verilog implementation.
Even if you have hardware design experience, manually translating C++ to Verilog will require some significant effort. I'd avoid that approach unless HLS or SDSoC doesn't give you the performance you need.
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Start using OpenCL SDAccel or Intel SDK. OpenCL has verbose and well defined API - which is a good thing. It is very easy to learn and you can have parallel code execution similar to multi-module instances of Verilog/VHDL. OpenCl vs. HLS has benefits in not requiring to re-invent the whole system for managing data, I/O, pipes. etc. You get quite a bit of helper logic in OpenCL BSP (Intel) or shell (XILINX). Yeah, and start reading these long guides.
