How to read memory value at a specific location using VPI and verilator?

I want to trace the memory value at specific locations during simulation of a hierarchical design using Verilator. A short version of the memory model is defined as follows

`module tc_sram{

parameter int unsigned NumWords     = 32'd1024,

parameter int unsigned AddrWidth = (NumWords > 32'd1) ? $clog2(NumWords) : 32'd1,

parameter type         data_t    = logic [DataWidth-1:0],

}{

data_t sram [NumWords-1:0] /*verilator public*/;

}`

I want to use VPI interface in the design's C++ testbench to trace memory value at any location I want, meaning I provide the address of the memory location in the testbench, and the memory value at this location will return. Does anyone have any idea?

Your memory model is not represented by a verilog code. I am not familiar with vpi implementation in verilator. However, using a standard vpi you can use vpi_handle_by_index to access memory elements.

I have an example below. First, some real System Verilog code:

module tc_sram #(
                 parameter int NumWords = 32'd8,
                 parameter int AddrWidth = (NumWords > 32'd1) ? $clog2(NumWords) : 32'd1,
                 parameter int DataWidth = 4,
                 parameter type data_t = logic [DataWidth-1:0]
                 )();
   data_t sram [NumWords-1:0] /*verilator public*/;
endmodule // tc_sram


module top;
   tc_sram sram();

   initial begin
      $testme(); // one of the possible ways to invoke vpi from verilog.
   end
endmodule // top

here is an example of vpi code which you can use as a base. It prints types of the variables. You would need to use vip_get_value/vpi_get_value_array and vpi_put_value/vpi_put_value_array to read/write values to the memory.

The following example only uses vpi_get_handle_by_index to print types.

#include <stdio.h>
#include <vpi_user.h>

void testme() {
    // get sram handle using instance path.
    vpiHandle arr = vpi_handle_by_name("top.sram.sram", 0);
    printf("sram: %s\n", vpi_get_str(vpiType, arr));


    // traverse array elements by index. You can use vpi_iterat/vpi_scan instead. 
    int indx = 0;
    vpiHandle el;
    while ( (el = vpi_handle_by_index(arr, indx)) ){
        printf("   el[%d]: %s\n", indx, vpi_get_str(vpiType, el));
        indx++;
    }   
}