Selecting a wreal Resolution Function

You can define a resolution function for each net in a design on a per scope basis by using the Verilog-AMS discipline mechanism. You can also designate a global resolution function that can be used for undisciplined nets and for the nets with disciplines that do not define a wreal resolution function.

You can define resolution function in the following ways:

• Defining a wreal Resolution Function for a Discipline. You can define wreal resolution functions for a discipline in the following two methods:

  • Defining a Resolution Function Directly in the Discipline Definition. To define a wreal resolution function for a discipline, use the realresolve parameter in the discipline definition. The syntax of this parameter is as follows:

    realresolve  resolveFunction

    where the resolveFunction be any of the predefined wreal resolution functions such as default, fourstate, sum, avg, min, max, none. See Predefined wreal Resolution Functions.

    Note that wreal resolution function names are case-sensitive. Therefore, if you specify the sum resolution function name as Sum or SUM , it will result in an error.

    If you specify the value of resolveFunction as none, it is equivalent to not using the realresolve parameter at all. Nets of such disciplines use the global resolution function. An error occurs if an invalid value is specified for the resolveFunction variable.

    The following example defines a discrete discipline named wrealavg that uses the avg resolution function for wreal nets.

    discipline wrealavg
    
        domain discrete;
    
        realresolve avg;
    
    enddisicipline

  • Defining a Resolution Function with the AMSCB connectmap Card. You can use the realresolve parameter with the connectmap card to define a resolution function for one or more disciplines. See connectmap.

• Defining a Global wreal Resolution Function. You define a global wreal resolution function in the following two methods:

  • Defining Global wreal Resolution Function Using -wreal_resolution. You can use the -wreal_resolution command-line option with xmelab or xrun to specify how you want the elaborator to resolve wreal nets that have more than one driver. The format of this command-line option is as follows:

    -wreal_resolution resolutionFunction

    where resolutionFunction can be any of the predefined wreal resolution functions such as default, fourstate, sum, avg, min, max, none. See Predefined wreal Resolution Functions.
    
    

    If you do not specify a resolution function using this command-line option, the elaborator uses the default resolution function algorithm.

    For those cases where the elaborator issues a run-time warning message, you can cause the message to be fatal using the -xmfatal command-line option. For more information about this option, see -xmfatal.

    The none resolution function is not a valid option to -wreal_resolution. It is only a valid value to the realresolution parameter of the discipline. An error will be issued if none is passed as an argument to -wreal_resolution.

  • Defining Global wreal Resolution Function Using the AMSCB connectmap Card. For a connectmap card, if the discipline parameter is absent, the resolution function specified by the realresolve parameter applies globally to all disciplines that are not covered by other connectmap cards.

    Consider the following example:

    amsd{

         connectmap realresolve=max

         connectmap discipline="disc1 disc2" realresolve=min

         connectmap discipline="disc3 disc4" realresolve=sum

         }

    In the above example:

    • The disc1 and disc2 disciplines will have the resolution function min.

    • The disc3 and disc4 disciplines will have the resolution function sum.

    • Any other discipline will have the resolution function max.

Order of Precedence for Determining the Resolution Function on a Net

If a discipline has a resolution function defined in the discipline definition and also has a resolution function defined in the AMS Control Block using the connectmap card, the connectmap card resolution function will take precedence and will be used as the resolution function for all nets of that discipline. This allows you to override the resolution function without changing the discipline definition.

Following is the order of precedence for determining the resolution function on a net:

1. Explicitly declared resolution on a net it is connected to (typed wreal or SV-RNM nettype)
2. Resolution function explicitly defined in the AMS Control Block using the connectmap card
3. Resolution function explicitly defined in the nets discipline definition
4. Resolution function of the discipline of the net to which a given net is connected
5. Global resolution function specified with the -wreal_resolution command-line option
6. Global resolution function specified with the connectmap card (without the discipline parameter)
7. The default global resolution function

Rules to Determine the Resolved Resolution Function for Connected wreal Nets

During elaboration, the connected wreal nets are collapsed into a single simulated wreal net with a single resolution function. The resolved value of this simulated wreal net is determined by considering all its drivers and processing their values through the resolved resolution function.

The set of rules listed below are followed to determine the resolved resolution function.

• If all connected wreal nets have the same resolution function, the resolved resolution function is that resolution function.

  The connected wreal nets need not have the same discipline as long as the resolution function of each net is the same.

• If two or more wreal nets are connected together and they do not have the same wreal resolution function, an error occurs.
• If a wreal net does not belong to any discipline or its discipline does not have a specified resolution function, the resolution function of the wreal net is the global resolution function. When a wreal net with the global resolution function is connected to other wreal nets, its resolution function is ignored for the purpose of determining the resolved resolution function for the connection.

• If none of the wreal nets in a connection has a specified resolution function, the resolved resolution function for the connection will be the global resolution function.

The table below summarizes how the resolved resolution function is determined from the resolution functions of the three wreal nets: w1, w2, and w3.

Related Topic

• Predefined wreal Resolution Functions