clarification required regarding VHDL.

Discussion in 'Programmer's Corner' started by saraswathi.95, Jan 27, 2014.

  1. saraswathi.95

    Thread Starter Member

    Apr 11, 2013
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    hello,
    from the theory that i have read ,VHDL and verilog are introduced so that all manufacturers can work under single platform ,useful and portable .
    i am unable to understand how they could do that?
    i,e. for given specifications all try to implement digital logic to get required logic output,then why they are not portable if all do not use same platform(VHDL).
     
  2. tshuck

    Well-Known Member

    Oct 18, 2012
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    VHDL and Verilog are high-level Hardware Description Languages (HDL), that, like a program written in C, must be compiled into a lower language for use by a certain device. In most cases, VHDL and Verilog are used in FPGAs, with each FPGA having a different implementation than another FPGA. The resources available may be different just among FPGAs, and this doesn't even consider other Programmable Logic Devices (PLDs) like CPLDs, which are an entirely different technology altogether. Without having a single implementation, it becomes impossible to implement a few lines of a HDL the same across all technologies.

    In short, while the languages (VHDL & Verilog) are standardized, their implementation is both compiler and hardware dependent.
     
  3. Brownout

    Well-Known Member

    Jan 10, 2012
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    That's not exactly true. There are many design input methods besides Verilog and VHDL which are portable. In addition, VHDL and Verilog can be interfaced with many other design methods, including graphical (drawing gates) C/C++, SystemC, various netlist representations and others.
     
  4. saraswathi.95

    Thread Starter Member

    Apr 11, 2013
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    Thank you,
    i really did not understand the concept of portability,can any one help me in understanding it clearly.
     
  5. tshuck

    Well-Known Member

    Oct 18, 2012
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    In this context, it means you can take VHDL from one device and recompile for another with minimal changes (provided enough resources).
     
  6. saraswathi.95

    Thread Starter Member

    Apr 11, 2013
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    Can you elaborate it if possible.
     
  7. tshuck

    Well-Known Member

    Oct 18, 2012
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    That's pretty basic...more of an explanation will be more complex, but here we go...

    You take the intended operation of a device (described using VHDL, Verilog, etc.) and pass it to a series of programs that will create a configuration for a particular device.

    The configuration is responsible for implementing logic using the hardware available in the FPGA. This configuration will be device specific, so, while the VHDL is portable, it must be compiled and synthesized for a particular device.
     
  8. Brownout

    Well-Known Member

    Jan 10, 2012
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    As an example, say you code up a UART for your project. You test it and verify it works. Then, I need a UART for my project. If your UART is portable, I can take your code and integrate it into my project and use it. Thus, I have ported your UART to my design.
     
  9. saraswathi.95

    Thread Starter Member

    Apr 11, 2013
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    Thank you,
    Can you tell me how these description languages like vhdl are able to program fgpa's(not simulation but i am concerned about synthesis.
     
  10. tshuck

    Well-Known Member

    Oct 18, 2012
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    See post # 2
     
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