signals in Procedure

Discussion in 'VHDL' started by Ved, Sep 12, 2006.

  1. Ved

    Ved Guest

    Hi all,

    Here is a syntex for procedure declaration:

    procedure my_proc (parameter_interface_list)
    {subprogram declarative part}
    {sequential statement}
    end procedure;
    Where are signals defined in procedure ? (These signals are used for
    implementing pipelining)

    For example how will below signal be defined in procedure ?
    if I decleare it in (parameter_interface_list) as

    SIGNAL dat1s0: std_logic_vector(15 DOWNTO 0);
    than it is assumed to be as input and I can't do something
    like this
    dat1s0 <= in1;
    Where in1 is the input .

    All the examples in books use variables in {subprogram declarative
    part} .
    So ambiguity remains in my mind regarding usuage of intermediate
    signals in procedure.

    Am I clear with my question ?
    Should I paste my codes ?

    Ved, Sep 12, 2006
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  2. You can't declare signals in a procedure.

    You can have parameters declared as signals though. The signals they
    are associated with (connected to) are declared in the architecture.
    Paul Uiterlinden, Sep 12, 2006
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  3. Ved

    Andy Guest

    You cannot declare signals inside a procedure, but if the procedure is
    defined inside a process, then it has visibility and can assign to any
    signal that is visible to the process.

    When you say you need pipelining in the procedure, remember that most
    synthesis tools do not accept subprograms (functions or procedures)
    with wait statements. Therefore the entire procedure has to operate in
    one clock. If it is called once every clock then it can implement

    Variables can also imply registers if they are read before being
    written during a clock cycle execution, forcing them to "remember" the
    value from the last clock. Note that variables declared internally to
    the procedure have no "memory" from one execution of the procedure to
    the next, and therefore cannot be used for registers. Variables
    declared before the procedure in the same process do. They can either
    be accessed directly, or passed as inout parameters to the procedure.

    Andy, Sep 12, 2006
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