Question

This interface example shows how to define tasks in one module and call them in another, using modports to control task access.

interface simple_bus (input bit clk); // Define the interface
    logic req, gnt;
    logic [7:0] addr, data;
    logic [1:0] mode;
    logic start, rdy;

    modport slave( input req, addr, mode, start, clk,
                   output gnt, rdy,
                   ref data,
                   export task Read(),
                   task Write());
                   // export from module that uses the modport

    modport master(input gnt, rdy, clk,
                   output req, addr, mode, start,
                   ref data,
                   import task Read(input logic [7:0] raddr),
                          task Write(input logic [7:0] waddr));
                   // import requires the full task prototype
endinterface: simple_bus

module memMod(interface a); // Uses just the interface keyword
    logic avail;

    task a.Read; // Read method
        avail = 0;
        ...
        avail = 1;
    endtask

    task a.Write;
        avail = 0;
        ...
        avail = 1;
    endtask
endmodule

module cpuMod(interface b);
    enum {read, write} instr;
    logic [7:0] raddr;

    always @(posedge b.clk)
        if (instr == read)
            b.Read(raddr); // call the slave method via the interface
            ...
        else
            b.Write(raddr);
endmodule

module top;
    logic clk = 0;
    simple_bus sb_intf(clk); // Instantiate the interface
    memMod mem(sb_intf.slave); // exports the Read and Write tasks
    cpuMod cpu(sb_intf.master); // imports the Read and Write tasks
endmodule