Re: VHDL syntax

Discussion in 'VHDL' started by Andy, Apr 24, 2007.

  1. Andy

    Andy Guest

    On Apr 23, 4:36 pm, Jim Lewis <> wrote:
    > Grumps,
    >
    > > What synthesiser feature/specification suggests compliance?

    >
    > IEEE 1076.6 specifies VHDL RTL Coding. Unfortunately 1076.6-2004
    > (the most current) states:
    > For a discrete range that appears as part of a slice name,
    > the bounds of the discrete range shall be specified
    > directly or indirectly as static values belonging to an
    > integer type.
    >
    > I am not sure about your application, but for some of mine,
    > this needs to be updated.
    >
    > In general, if you have issues of language compliance, in which
    > different vendors disagree or you and a vendor disagree, and
    > you can get cooperation from the vendor, you can
    > also get an official language resolution from the VHDL Issues
    > Screening and Analysis Committee (ISAC). Please make sure to
    > keep the vendor's name out of the issue report - the ISAC worries
    > about compliance - once you receive the compliance report, you
    > can deal with the vendor. =You can report issues to ISAC at:
    > http://www.eda-stds.org/vasg/#Enhancements
    >
    > For synthesis issues click on: "Report a BUG on an IEEE VHDL revision"
    >
    > Best Regards,
    > Jim Lewis
    > IEEE VHDL and Analysis Standards Group (VASG) Chair
    > SynthWorks VHDL Training


    While most synthesis tools will accept non-static expression in
    ranges, they also usually must implement the computational circuitry
    for those expressions in hardware.

    If it is possible to code it in a for loop with an if statement,
    comparing the unadulterated signal to an expression of the index, then
    the index is treated as if "static" when the loop is unrolled, and the
    computation of the expression is not done in hardware. Therefore such
    expressions are also not limited by what is implementable in hardware
    (i.e. divide/modulo by non-integral-powers of two, etc.).

    Andy
     
    Andy, Apr 24, 2007
    #1
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