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What's the definition and the function of value()

TaoZ

Hi, all

I'm new to specman E, and begin learning it by reading Design Verification with E. I've many times the utilization of function value, such as:

keep tx_monitor.file_logger.to_file == value(tx_log_filename);

keep tx_bfm.driver == value(tx_driver);

Could anyone explain me about the utilization of value().

Many thanks!

Tao

  • When 2 variables are linked by a constraint, they are in a bidirectional relationship. E.g keep a>b links a and b, so b needs to be bigger than a and a smaller than b.
    Sometimes you don't want a bidirectional relationship, e.g. keep a = crc_function(data). So here a and data are in a unit-directional relationship. Data needs to be generated
    before a, and then the function is called and the result assigned to a.

    value() is just a function call returning the value. But for the generator, it also create a unidirectional relationship. To assign pointers in a testbench, the use of value() (or read_only()) is recommended. Generally testbench containers (units) are created in a specific order, and there are no bidirectional relationships. And to assign a pointer to something that already exists, just use value() or read_only()

  • in reply to hannes

    Hi, Hannes

    Thanks for your reply, which make me have a better understanding of value().

    Nice Weekends!

    Tao

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