how can I convince iverilog that the vpi is a system function and not a task

Question

I am trying to use a vpi function in iverilog that will return a value to the verilog test bench after it is called. It compiles ok but returns the following when I run

Error: $flash_dat() is a system task, it cannot be called as a function.

I have put the relevant portions of the code below. I would appreciate it if I can either get an example including the compile and run process of using a vpi function that returns a value in iverilog (I did search in google for but did not get any example for iverilog) or get a pointer to the mistake I made in this code. Thanks in advance for your time.

Thanks, Vinay

Code: verilog

always @(flash_adr) #110 flash_do <= $flash_dat(flash_adr);

.sft file

$flash_dat vpiSysFuncInt

flash_dat.c

 void flash_dat_register()
 {
  s_vpi_systf_data tf_data;
  tf_data.type      = vpiSysTask;
  tf_data.tfname    = "$flash_dat";
  tf_data.calltf    = flash_dat_calltf;
  tf_data.compiletf = flash_dat_compiletf;
  tf_data.sizetf    = 0;
  tf_data.user_data = 0;
  vpi_register_systf(&tf_data);
}

void (*vlog_startup_routines[])() = {
flash_dat_register,
0
};

static unsigned int flash_dat_calltf()
{
unsigned int addr= tf_getp(1);
tf_putp (0,((flash_array[addr+1]<<16)|flash_array[addr]));
return ((flash_array[addr+1]<<16)|flash_array[addr]);
}

Compile:

SOURCES=tb_norflash16.v flash_dat.sft $(wildcard ../rtl/*.v)

all: tb_norflash16 flash_dat.vpi

isim: 
vvp -M. -mflash_dat tb_norflash16

tb_norflash16: $(SOURCES)
iverilog -o tb_norflash16 $(SOURCES)

flash_dat.vpi: flash_dat.c flash_dat.sft
iverilog-vpi $^

Answer 1

The answer was kind of right in front of my eyes I need to change

tf_data.type      = vpiSysTask;

to

tf_data.type      = vpiSysFunc;

Thanks for the help

Answer 2

I don't think this is supported by Icarus Verilog. If you take a look at the ivltest suite for vpi the tests are system tasks rather than functions.

You should be able to achieve what you want by re-writing as a task invocation, and driving the input/output nets from VPI. Look at pokereg.cc and pokereg.v