Hi, Further to the discussion in SV-CC meeting on 4/26, I have compiled references from the LRM related to invocation of export functions/tasks. Of all the references from the LRM, there is only instance which can be used to construe invocation of export tasks and functions fron non (context) import scope. This is the first of the references I present below. After that, all the references presented can be interpreted to indicate that export functions/tasks and utility functions can be called only from context imported tasks and functions. Regards, --Amit A. Reference which can be used to deduce invocation of export tasks/functions from non-import contexts 1. Section 26.4.3: Context tasks and functions - second paragraph "The SystemVerilog context of DPI export tasks and functions must be known when they are called, including when they are called by imports. When an import invokes the svSetScope utility prior to calling the export, it sets the context explicitly. Otherwise, the context will be the context of the instantiated scope where the import declaration is located. Because imports with diverse instantiated scopes can export the same task or function, multiple instances of such an export can exist after elaboration. Prior to any invocations of svSetScope, these export instances would have different contexts, which would reflect their imported caller's instantiated scope. " Interpretation: The ending phrase for the first sentence above is the only place in the LRM where I can deduce that a DPI export task/function can be called from any place other than imports. B. References supporting invocation of export tasks/functions from context import tasks/functions 1 : Section 26.4.3:Context tasks and functions - second paragraph again The remainder of the paragraph explains the requirement of a context and how it is set from a context import task/function. This gives the explanation for presence of a context when DPI export tasks/functions are invoked. " The SystemVerilog context of DPI export tasks and functions must be known when they are called, including when they are called by imports. When an import invokes the svSetScope utility prior to calling the export, it sets the context explicitly. Otherwise, the context will be the context of the instantiated scope where the import declaration is located. Because imports with diverse instantiated scopes can export the same task or function, multiple instances of such an export can exist after elaboration. Prior to any invocations of svSetScope, these export instances would have different contexts, which would reflect their imported caller's instantiated scope." Interpretation: A context's presence is essential as when a SystemVerilog function corresponding to a function is to be executed, it s associated scope/context should be available. In case a design unit containing an import task/function has been instantiated multiple times then svSetScope() allows setting the context to a particular instance of the task/function that needs to be executed. In the absence of an explicit call to svSetScope() since there is a default scope (that of the called import function/task) already available, there are no serious consequences (crash?). In case a call to an export task/function is made without a context then the simulation tool does not have any scope/context in which the function should be executed and thus the restriction. Further in the same vein, this section IEEE26.4.3, states, 2 : Section 26.4.3: Context tasks and functions : fourth paragraph " Only calls of context imported tasks or functions are properly instrumented and cause conservative optimizations; therefore, only those tasks or functions can safely call all tasks or functions from other APIs, including PLI and VPI functions or exported SystemVerilog tasks or functions. For imported tasks or functions not specified as context, the effects of calling PLI or VPI functions or SystemVerilog tasks or functions can be unpredictable; and such calls can crash if the callee requires a context that has not been properly set..." Interpretation: From the above I understand that invocation of export tasks and even VPI/PLI API from import tasks/functions requires the import tasks/functions to be specified as context. 3. Annexure F.8 : Context tasks and functions : second paragraph States unambiguously that calling scope related utility functions from non context import tasks functions will be a system error "To avoid any unnecessary overhead, imported task and function calls in SystemVerilog code are not instrumented unless the imported task or function is specified as context in its SystemVerilog import declaration. A small set of DPI utility functions are available to assist programmers when working with context tasks or functions (see F.8.3). If those utility functions are used with any noncontext function, a system error shall result. " Interpretation: This paragraph precludes all C functions except context import tasks and functions from calling DPI scope utility functions. The only other way a scope for an export function is set is the scope set of the executing context import task/function. This along with item 1, in this section, in my belief states that export tasks and functions cannot be executed from any C function other than context import tasks and functions. 4. Annexure F.8.3: Working with DPI context tasks and functions in C code : second paragraph "There are functions that allow the user to retrieve and manipulate the current operational scope. It is an error to use these functions with any C code that is not executing under a call to a DPI context imported task or function." Interpretation: This paragraph is effectively saying the same thing as in item 3 above. Should be sufficient to conclude that export tasks and functions cannot be executed from any C function other than context import tasks and functions.Received on Mon, 8 May 2006 20:13:15 +0530
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