using entity attributes for pin number assignments

Discussion in 'VHDL' started by Neil Zanella, Oct 19, 2003.

  1. Neil Zanella

    Neil Zanella Guest

    Hello,

    I would like to know whether using attributes inside entity declarations
    to assign pin numbers to signals as opposed to using a user constraints
    file (.ucf file) is portable or whether it's a vendor specific extension.
    Does the VHDL standard itself support such constructs, or are
    implementations free to use attributes in implementation
    define manners?

    Thanks,

    Neil
     
    Neil Zanella, Oct 19, 2003
    #1
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  2. On Sun, 19 Oct 2003 16:29:36 -0230, Neil Zanella <>
    wrote:

    >
    >Hello,
    >
    >I would like to know whether using attributes inside entity declarations
    >to assign pin numbers to signals as opposed to using a user constraints
    >file (.ucf file) is portable or whether it's a vendor specific extension.
    >Does the VHDL standard itself support such constructs, or are
    >implementations free to use attributes in implementation
    >define manners?


    The VHDL standard only defines the syntax for attributes. The meaning
    is up to the tool. I guess an ideal synth tool would pass any
    attributes it didn't recognise straight through to the EDIF. Most
    tools I've used seem to do this quite well, except XST (which knows
    which attributes are supported by the back end tools).

    I have successfully used attributes in an architecture to assign pin
    numbers.
    I have also used UCF to assign pin numbers.

    I prefer the UCF, as the PCB package we use here spits out the correct
    UCF (via a Perl script). I can allow the PCB designer to swap pins
    (allowing for various banking and SSO rules, etc.) and I don't have to
    worry about changing my VHDL source.

    Regards,
    Allan.
     
    Allan Herriman, Oct 22, 2003
    #2
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  3. Neil Zanella

    Neil Zanella Guest

    I agree with you. It seems that using the UCF file for pin assignments
    is both more flexible and more portable. A design should be as independent
    of the hardware it is implemented on as possible and should have the potential
    to be synthesized by a variety of tools and to a variety of distinct hardware.

    Regards,

    Neil

    Allan Herriman <> wrote in message

    > I prefer the UCF, as the PCB package we use here spits out the correct
    > UCF (via a Perl script). I can allow the PCB designer to swap pins
    > (allowing for various banking and SSO rules, etc.) and I don't have to
    > worry about changing my VHDL source.
    >
    > Regards,
    > Allan.
     
    Neil Zanella, Oct 26, 2003
    #3
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