Do constants need to be in anon-clk'd process's sensitivity list if they are i/ps

Discussion in 'VHDL' started by neilmac, Feb 7, 2008.

  1. neilmac

    neilmac

    Joined:
    Jan 10, 2008
    Messages:
    5
    If Ive got a proces like this, which is basically combitorial, do constants need to be in the sensitivity list?

    I think not.

    In my case the constant is defined in another package, not within the architecture.

    Ive put a much simplified examle below where:

    inq_addr is an input and REGISTERS_BASE_VALID is a constant.

    -------------------------------------------------
    -- address decode process
    ---------------------------------------------------

    p_addr_decode: process(inq_addr)


    begin

    access_type_selected <= NODEV;


    if ((inq_addr AND REGISTERS_BASE_VALID) then

    access_type_selected <= REGISTER_ACCESS;

    end if;


    end process p_addr_decode;

    Any help appreciated..
     
    neilmac, Feb 7, 2008
    #1
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  2. neilmac

    mcdjnaja

    Joined:
    Feb 7, 2008
    Messages:
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    Hello,

    I think a constant must not be in the sensitivity list because it is constant and a process is evaluated when a signal of the sensitivity list is modified, although a constant will never be modifed.
    Moreover, at the synthesis time, synthesis tool will detect the constant and remove it.

    Mathieu
     
    mcdjnaja, Feb 7, 2008
    #2
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  3. neilmac

    mcdjnaja

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    More, a signal in the sensitivity list of a process can be replaced by a "wait on" instruction in concurrent statement, so you can wait a long time the modification of a constant...
     
    mcdjnaja, Feb 7, 2008
    #3
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