System Verilog DPI Example

String passing example

Download as PDF document.

 systemverilogdpi.pdf

1) For illustration strings are used;
But strings can’t be used in module ports;
2) Use SystemVerilog “program” instead of “module” for testbenches.
See this: SystemVerilog program example

//  dpi_top.v

module top ();

import "DPI-C" context v2c_c=

task v2c_sv(input string a);

import "DPI-C" context c2v_c=

function string c2v_sv();

export "DPI-C" print_string_c =

function print_string_sv;

string v2c_string,c2v_string;

function void

print_string_sv(input string aaa);

$display("Exporting VerilogFunction:%s", aaa);

endfunction

initial

begin

v2c_string = "A v2c_string";

v2c_sv(v2c_string);

c2v_string = c2v_sv();

$display("c2v_string: %s n",

c2v_string);

$finish;

end

endmodule

// dpi.h
#include “svdpi.h”

#ifdef __cplusplus
extern “C” {
#endif

extern void print_string_c (const char *_a1);

#ifdef __cplusplus
}
#endif

//  dpi_main.c

#include <stdio.h>

#include "svdpi.h"

#include "dpi.h"

#include "veriuser.h"

void v2c_c(char* v2c_string)

{

io_printf("v2c_string: %sn",v2c_string);

print_string_c("string passed from C");

}

char* c2v_c(void)

{

char* c2v_string;

c2v_string="This is c2v_string";

//io_printf("c2v_string: %sn",

//c2v_string);

return c2v_string;

}

#####   shell script to run simulation

 ncverilog +sv dpi_top.v +elaborate +ncelabargs+-messages

 gcc -fPIC -shared -o dpi_main.so  dpi_main.c  -I/$CDS_INST_DIR/tools.lnx86/inca/include

 ncverilog +sv dpi_top.v +sv_lib=dpi_main.so +access+r +ncsimargs+"-sv_root ./"   

Download NCVerilog demo here.

 systemverilogdpi.pdf

 Here is a demo for running the same example 

using Modelsim under Windows.

System Verilog DPI Modelsim

Download Modelsim demo here.

system-verilog-dpi-modelsim.pdf

XOR Gate

The exclusive-OR gate performs modulo 2 addition of its inputs.

When you cascade q two-input exclusive-or gates, with the output of the first one feeding one of the inputs of the second one, the output of the second one feeding one of the inputs of the third one, etc., the output of the last one in the chain is the modulo-two sum of the q + 1 inputs.  This could be used as a parity detector.