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 SVUG Community Forum
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AMAL
Posts:24
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| 10/15/2008 1:59 PM |
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The return values from a SyetemVerilog DPI function cannot be a struct or complex type. Only simple types are supported. My question is how does one pass structs back to SystemVerilog from C/C++?
Should I instead of returning the struct, use output arguments?
Another question is regarding typedefs and structs that one defines in SystemVerilog. I have a number of functions that need a struct as arguments. If I define them in SystemVerilog, they will be placed in the .h file automatically (by modelsim) and then they conflict with the already defined structs in the C domain.
What is the best method to do this? Should I generate the header file once and manually modify it?
-- Amal
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DAVE
Posts:56
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| 10/15/2008 6:55 PM |
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Yes, use an output argument for imported DPI-functions.
You do not need to use the generated header file from Modelsim in your C/C++ code, but I suggest that you figure out a way to use it without modification as it provides a level of memory reference safety.
Dave
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ANSHUMAN
Posts:3
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| 10/16/2008 12:10 PM |
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Replying to your second question, I think you can use packages to restrict the scope of your structures, and then they wont be visible outside the scope.
Anshuman |
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AMAL
Posts:24
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| 10/16/2008 1:49 PM |
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My problem is not the SystemVerilog scope, but C/C+ scope. The structure is defined in a C/C++ header (.h) file and I need to redefine it in SystemVerilog to be able to pass it to/from the function. But if I define it in SystemVerilog, it will be automatically be placed in the dpiheader.h file. And that conflicts with the previously defined structure in .h file.
-- Amal
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HOLGER
Posts:1
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| 09/09/2009 7:23 AM |
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Hi Amal,
basically you need to use a pointer to pass more "complex" data types e.g. strings and structs. Furthermore, the struct can be redefined in SystemVerilog with a different name in order to avoid conflicts.
Example:
--- C code ---
typedef struct {
double a;
double b;
} results_t;
void myFunction (const char *file, results_t* results) {
...
}
--- SV code ---
package my_pkg;
// Redefine struct in SV with different name //
typedef struct {
real a;
real b;
} results;
import "DPI-C" function void myFunction (input string file, output results my_results);
function dpi_myFunction(input string file, output results my_results);
begin
myFunction(file, my_results);
end
endfunction
endpackage
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bernard
Posts:1
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| 10/09/2009 4:18 AM |
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I have a related problem in a SceMi 2.0 transactor. The transactor uses synthesizable Verilog and needs assignments like:
register_d = AXI32_SlaveTransactor_SetResponse( register_q );
where the function is defined as:
import "DPI-C" context function bit[AXI32_ArgT_width-1:0] AXI32_SlaveTransactor_SetResponse(input bit[APB3_32ArgT_width-1:0] TArg);
which supposes the signature in the C/C++ domain is something like:
extern "C" svBitVecVal* AXI32_SlaveTransactor_SetResponse(const svBitVecVal *MsgVector);
I'm hitting a problem with the allocation of the storage for the return value. I don't have the flexibility to add a second argument, but if I assign space inside the function it never gets deleted and the application leaks memory. If I return a pointer to automatic storage inside the function it goes out of scope on return.
Is there a DPI guru out there who knows how this should have worked?
Thanks in advance,
Bernard |
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Ankit
Posts:1
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| 11/26/2009 12:29 AM |
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Hi Bernard,
You can declare a global pointer and allocate its memory dynamically, may be invoking a dpi call from hdl side, in the end
when you are done with the memory, u may call another dpi , to destroy this dynamically created vector.
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