SystemVerilog DPI in NCSim?

Davy

I believe there are some examples on using DPI in the NC documentation. The essential step you need are:

1. Compile the c code as usual to .o files.
2. Link the C code to a shared library. You must make sure that if you have C++ code, the DPI method should be declared under extern "C" {

} block.
3. Specify the shared library path to the -sv_lib option in ncsim.

Nitin

Hello Davy.

Currently you are required to compile the DPI C code yourself, though I believe this will change in the not too distant future.

Compilation is pretty easy, and if you build a shared library with the name "libdpi.so" then the simulator will automatically load this, so you don't have to specify the library file to ncsim.

Here's an example:
  gcc my_c_funcs.c -fpic -shared -o libdpi.so
  ncverilog +sv my_testbench.sv

Clearly if you need to pull in more C code, or merge lots of *.o files there is more to do in the gcc side, but the ncsim invocation remains the same.


Steve.

Here's a small example that you can compile and run.
The Run.sh shows how to compile the C code.

Also, in recent versions of IUS, you can find a tutorial on DPI, accessed by either:

A) Run the "cdsdoc" command, expand the "NC-Verilog" or "Incisive Unified Simulator" hierarchy, and look for the topic "SystemVerilog DPI Engineering Notebook".


B) cd to `ncroot`/doc/dpiEngrNtbk, then open the PDF file. This directory contains the example designs in the "import" and "export" directories.


Steve.

Hi stephenh,

Thanks a lot!

1. You give out a gcc compile and link example. Is the switch listed in the example all gcc original switch or added by Cadence? Is there any recommendation reading about gcc used in IUS SystemVerilog DPI? For I am a Microsoft VC user and not familiar with GNU tools.
2. Attachment: dpi_example.tar.gz seems cannot be open, can you check it?

Best regards,
Davy

Hi Davy.

Cadence does not modify the gcc tool, so all the options I showed previously are standard gcc ones.
"gcc --help" will giv you lots of detail.

The options I used are:
"-fpic" : create relocatable code
"-shared" : create a shared lib rather than a statically linked binary
"-o libdpi.so" : sets the name of the output file

One other flag you may need is "-m32", which sets the compiled code for 32 bit mode if you compile on a 64 bit machine.

Regarding the dpi_example.tar.gz, the version I uploaded is OK, but when I download it, the file is corrupted. I'll try uploading it again here, and if that fails, feel free to email me directly and I'll send it to you by email.

Regards,
Steve.

Hi stephenh,

Thanks a lot for the explanations! The new uploaded dpi_example.tar work OK! I will take some time to learn how to write a makefile when I need to include a bunch of C file, do you think so?

I heard that SV DPI can be used to link SystemC code. Shall I run SystemC code like the normal C file, or shall I add something else? Or is there some reference document from Cadence? Thanks in advance!

Best regards,
Davy

Hi,

You may want to try and use "ncsc_run" utility. This is primarily used for compiling systemc c code and creating a simulator. This utility when used with -dynamic and "-stop link" would create a shared library for you. It takes a list of all your C/C++ files as input, automatically generate the Makefile, compiles all the files as neccesary and than links them.

This is what we use in our environment and it really simplifies the process as we no longer have to maintain the Makefiles. In our environment we have systemc and DPI both compiled in a same shared library and we use "ncsc_run" to compile it. It works great.

In order to link systemc and dpi together, compile them using ncsc_run (it takes care of linking systemc and other housekeeping stuff) as I describe above. Then specify the same shared file at -load_sc command line option at ncelab time and -sv_lib option at ncsim time and it should work.

Nitin

Nitin

Hi Nitin,

Thanks lot for provide the "ncsc_run" utility information. And I am not familar with SystemC/SystemVerilog co-simulation. Is there any document given by Cadence talk about something like "ncsc_run" utility?

Best regards,
Davy

Here’s the basics of creating a simple dpi file and using it from Ncsim.  In this example the simulator gets a real value from dpi and then passes it back to the dpi code.  I have numerous other examples using strings, integers...etc (tmackett@cadence.com)

Here’s the Verilog file (real_test.sv) :

module real_test ();

// map the C function name to the Verilog function name

import "DPI-C" context get_real_c = function real get_real_v ();

import "DPI-C" context put_real_c = function void put_real_v (real x);     

real pi;

initial

begin

$display("real_test");

pi = get_real_v();        // get a real number from the C code

$display("pi = %f", pi);  // display it

put_real_v(pi);           // send the real number back to C code  

end

endmodule

Here’s the dpi code (real_dpi.c).  Notice there is NO c main:

#include "svdpi.h"

// since we are using math functions, include the math library

#include         

// can use io_printf() instead of printf() to put into ncsim.log file

double get_real_c() {  // imported SV function

  // exercise DPI function - get calling scope

  printf("Function Calling HDL scope is %s \n", svGetNameFromScope(svGetScope() ) );

  return 3.14159;

}

void put_real_c(double n) {  // imported SV function

  // exercise DPI function - get calling scope

  printf("Function Calling HDL scope is %s \n", svGetNameFromScope(svGetScope() ) );

  printf("pi + 5.0 = %f\n", n+5.0);      

}

Here’s the script to compile everything:

rm -r INCA_libs

rm -r waves.shm

rm *.so

# make sure LD_LIBRARY_PATH includes . (or where the real_dpi.so lives)

# make sure using useful gcc version like 3.2.2, 3.3.3 etc

#create single header file for multiple dpi.c sources

ncvlog real_test.v -sv

# -dpiheader produces nothing for imported functions

ncelab -dpiheader dpi.h worklib.real_test:module

gcc -m32 -fPIC -g -shared -o real_dpi.so  real_dpi.c  -I/`ncroot`/tools/include

# use the Incisive supplied gdb

#xterm -e `ncroot`/tools/systemc/bin/gdb `ncroot`/tools/bin/ncsim &

Here’s the resulting log file:

ncsim> run

real_test

Function Calling HDL scope is real_test

pi = 3.141590

Function Calling HDL scope is real_test

pi + 5.0 = 8.141590

ncsim: *W,RNQUIE: Simulation is complete.

ncsim> exit

Hi,
I am seeing following errors while using ncsc_run:
ncsc: compiling $TESTDIR/adder_sysc_main.cpp
make: *** [INCA_libs/ncsc_obj/adder_sysc_main.o] Error 1
ncsc: *W,WRKNMP: Could not obtain library mapping for WORK, no SystemC intermediate form generated.
ncsc: Error executing: $CDSROOT/tools/systemc/gcc//bin/g++ -o INCA_libs/ncsc_obj/adder_sysc_main.o -DNCSC -I$CDSROOT/tools/systemc/include -I$CDSROOT/tools/tbsc/include -I$CDSROOT/tools/vic/include -I$CDSROOT/tools/systemc/include/tlm -c -x c++ -Wall $TESTDIR/adder_sysc_main.cpp
ncsc_run: *E,TBBLDF: Failed to generate object INCA_libs/ncsc_obj/adder_sysc_main.o


Any idea why I am seeing this error?