SOS: verilog array data got padded when calling into C!

SystemVerilog
1

this is the URL of the my code at EDA playground

In case you don’t have access, below code demonstrate the problem and output
// Example of using SystemVerilog DPI-C with C++ code.
//
// In EDA Playground, when using ModelSim,
// any *.cc file will be compiled as C++ and linked into the simulation.


module automatic test;
 
  import "DPI-C" function int tb_sm_io(inout logic[31:0] data_buf[],input int device_addr,input int size,input int direction);
  initial run();
 
  task run();
    
    logic a = 1'bx;
    logic [31:0] pay_load_data[];
    int result;
    pay_load_data = new[3];
    pay_load_data[0]=32'h12345678;
    pay_load_data[1]=32'h87654321;
    pay_load_data[2]=32'hDEADBEEF;
    $display("Before 1st call to tb_sm_io \n\tSV: pay_load_data[0]=%x",pay_load_data[0]);
    $display("\tSV: pay_load_data[1]=%x",pay_load_data[1]);
    $display("\tSV: pay_load_data[2]=%x",pay_load_data[2]);

    result=tb_sm_io(pay_load_data,pay_load_data[0],pay_load_data[1],pay_load_data[2]);
    $display("After return from 1st call to tb_sm_io\n\tSV: pay_load_data[0]=%x",pay_load_data[0]);
    $display("\tSV: pay_load_data[1]=%x",pay_load_data[1]);
    $display("\tSV: pay_load_data[2]=%x",pay_load_data[2]);

  endtask
 
endmodule


//C
// This file is compiled as C++ and linked with stdlib
// into the simulation executable.

#include <iostream>
#include <svdpi.h>
#include <stdio.h>
#include <assert.h>
using namespace std;
#define cdump(x) printf("\tC: %s=%x\n",#x,x)
extern "C" int tb_sm_io(svOpenArrayHandle data_buf_ref,int device_addr,int size,int direction) 
{
  unsigned int *pay_load_data=(unsigned int *)svGetArrayPtr(data_buf_ref);
  printf("Data Dump in C/%s pay_load_data=%p\n",__FUNCTION__,pay_load_data);
  cdump(pay_load_data[0]);
  //expect 0x87654321 == pay_load_data[1]
  cdump(pay_load_data[1]);
  assert(0x87654321 == pay_load_data[1]);
  cdump(pay_load_data[2]);
  pay_load_data[0]=pay_load_data[2];
  pay_load_data[1]=0x01234567;
  pay_load_data[2]=0x84219751;
  cdump(device_addr);
  cdump(size);
  cdump(direction);
  return 0;
}

//Result:
Before 1st call to tb_sm_io
SV: pay_load_data[0]=12345678
SV: pay_load_data[1]=87654321
SV: pay_load_data[2]=deadbeef
Data Dump in C/tb_sm_io pay_load_data=0xefd6efe0
C: pay_load_data[0]=12345678
C: pay_load_data[1]=0
simv: …/my_dpi.cc:17: int tb_sm_io(svOpenArrayHandle, int, int, int): Assertion `0x87654321 == pay_load_data[1]’ failed.

An unexpected termination has occurred in ./simv due to a signal: Aborted

2

In reply to MichaelSong:

You can’t dereference a svOpenArrayHandle as an array. You need to use ‘svGetArrayElemPtr()’ to get the data pointers for each array element. Refer to section H.12.4 of the LRM.

int tb_sm_io(const svOpenArrayHandle data_buf_ref,int device_addr,int size,int direction) 
{
  unsigned int *pay_load_data[3];
  pay_load_data[0] = (unsigned int *)svGetArrElemPtr(data_buf_ref, 0);
  pay_load_data[1] = (unsigned int *)svGetArrElemPtr(data_buf_ref, 1);
  pay_load_data[2] = (unsigned int *)svGetArrElemPtr(data_buf_ref, 2);

  cdump(*pay_load_data[0]);
  cdump(*pay_load_data[1]);
  cdump(*pay_load_data[2]);

  return 0;
}