Export DPI function question about the real type and realtime type

SystemVerilog
1

Here is my code below. I always got syntax error during the compilation. Can anyone help me here ?


realtime time1;
realtime time2;
always @ (posedge clk) begin
    time1 <= $realtime;
    time2 <= time1;
end

export "DPI-C" function get_period();

function realtime get_period();
    return (time1 - time2);
endfunction
2

In reply to zz8318:

It would help to provide the error message as well as a complete example.

I suspect that you have encountered a tool bug. realtime is synonym for real and real types are compatible with the float datatype in C.

This Mentor/Siemens EDA sponsored public forum is not for discussing tool specific usage or issues. Please read your tool’s user manual or contact your tool vendor directly for support.

3

In reply to dave_59:

Hi Dave,

A quick question here. Do I need to add the return data type in below code to specific ?

export “DPI-C” function ??? get_period();

4

In reply to zz8318:

No, you are just exporting the function name. Its prototype is in the function declaration.

5

In reply to dave_59:

Looks like I don’t need ‘()’ following the function name. It passed if I coded like below.

export “DPI-C” function get_period;

6

In reply to dave_59:

Hi Dave,

I have further question on this topic.

If I coded as below in SV side.


realtime time1;
realtime time2;
always @ (posedge clk) begin
    time1 <= $realtime;
    time2 <= time1;
end

export "DPI-C" function get_period;

function void get_period(output realtime rt);
    rt = (time1 - time2);
endfunction

And in Cplusplus side, how can I get the value rt ?

I coded as below but failed at compilation.
[c]
extern “C” void get_period(double &t);
…
double &t;
get_period(t);
[/c]

7

In reply to zz8318:

Repeating my suggestion, it would help to provide the error message as well as a complete example.

The following works for me on EDAPlayground.

#include "dpi.h"
#include <iostream>
using namespace std;
extern "C" void get_period(double* rt);
extern "C" void C_main() {
    double p;
    get_period(&p);
    cout << "Period is " << p << "\n";
}

Most tools provide an automatic header (dpi.h) file so you can match your code’s prototypes with the required prototypes and get a compiler error if they do not match.