VVP compiled as a library

[keroblabs]

Hi All,

It seems VVP tool is no longer available as a library to be linked with a bigger project simulation.
However I see it is possible to compile the VVP and include it in a project. Has anyone tried that? If I integrate the VVP into my simulation project, does the source code of this tool include all PLI API to exercise the HDL design?

My idea is to design a FPGA that will work with a microprocessor to interface with SRAM and some peripherals, simply speaking. I have everything constructed in an emulator, but I would want to replace C code with a PLI interface to exercise the FPGA as part of the design verification.

Thanks,
Marcio.

[martinwhitaker]

I don't know what you mean by "It seems VVP tool is no longer available as a library to be linked with a bigger project simulation.". AFAIK that was never supported in the past, but was enabled by PR #1068 which was merged a couple of months ago. And yes, the person who worked on that PR certainly tried it :-)

[keroblabs]

@martinwhitaker sorry for the confusion, I was looking at https://steveicarus.github.io/iverilog/usage/vvp_library.html and because this option was not available (v12-branch) I thought it was removed.

I looked the comments and PR and now I have doubts if that's what I need - can you help please?

Suppose I compile my FPGA design with:
iverilog -o my_design my_fpga.v
("my_design" will not include any testbench)
Then I use my_design to add the FPGA design into my emulator. That means my emulator is the actual testbench, it will not be the same as using iverilog-vpi.
Would that be possible with libvvp? If not, is there any support from iverilog for this sort of integration?

Thanks,
Marcio.

[martinwhitaker]

Yes, I think libvvp is what you want. Here is a simple example:

// hello.c

# include  <libvvp.h>
# include  <vpi_user.h>

static PLI_INT32 hello_calltf(PLI_BYTE8 *user_data)
{
    (void)user_data;
    vpi_printf("Hello\n");
    return 0;
}

static void register_vpi_tasks(void)
{
    s_vpi_systf_data tf_data;

    tf_data.type      = vpiSysTask;
    tf_data.tfname    = "$hello";
    tf_data.calltf    = hello_calltf;
    tf_data.compiletf = 0;
    tf_data.sizetf    = 0;
    vpi_register_systf(&tf_data);
}

int main(int argc, char *argv[])
{
    register_vpi_tasks();
    vvp_init(NULL, 0, NULL);
    return vvp_run("./hello.vvp");
}

// hello.v

module main();

initial begin
  $hello; 
  $finish;
end

endmodule

Compiled and run like this

iverilog -o hello.vvp hello.v
gcc -o hello -I /usr/local/include/iverilog/ -L /usr/local/lib -lvvp hello.c
./hello

The small flaw in the process is that libvvp.h is not currently installed in the target directory when you run make install, so you need to copy it yourself from the iverilog/vvp source directory. I'll aim to fix that omission.

You can use any of the VPI functions defined in vpi_user.h to bridge between your emulator and the vvp simulation.

[keroblabs]

Awesome! Thank you so much. I'm building from master branch and now I have the libvvp. I will build things around the example above.
Cheers.

[gatk555]

Hello Marcio,

If I had seen this discussion before today, I would have commented sooner: PR #1068 was from me, based on some earlier work. If you are interested in how I use libvvp, there is some code here. There I have been using a test harness to discover how to compile interface components with MSVC, on a machine without Iverilog installed. The aim is to use Iverilog to implement digital components inside the mixed-signal (but mostly analogue) simulator, Ngspice. The code linked is almost that same as that used with Ngspice and running for some months.

I would be interested to know more about how you are using libvvp, particularly how you are handling the problem of keeping two (or more!) simulators synchronised.

Giles

[martinwhitaker]

Hello Giles,

If you haven't seen https://forum.kicad.info/t/mixed-mode-simulation-including-c-code-and-verilog/49752, it might be of interest to you.

[gatk555]

Martin,

Thank you, very interesting. It is only the second web-published example that I have seen of an analogue simulation including a micro-controller with code execution. (And it links the other one.) Strange to me, since microcontrollers in analogue circuits are everywhere.

Giles

[Kreijstal]

its because its open source :)

[gatk555]

The code to use libvvp inside Ngspice is now in the development branch for the next NGspice release, probably due around December.

[gatk555]

An update: iverilog support using libvvp is included in Ngspice-44, released two days ago.

[martinwhitaker]

Nice. We really need a new Icarus Verilog release too.