module tb_top ();

    logic clk;
    logic nreset;

    clkgen clkgen_inst (
        .clk_o   (clk),
        .nreset_o(nreset)
    );

    gb gb_inst (
        .clk_i   (clk),
        .nreset_i(nreset)
    );

    // Testbench code
    logic        instr_undef;
    logic        halted;
    logic [15:0] last_pc;
    logic [ 7:0] last_opcode;
    logic [ 7:0] last_op1;
    logic [ 7:0] last_op2;

    logic        we;
    logic [15:0] address;
    logic [ 7:0] wdata;

    assign halted      = gb_inst.cpu_inst.control_inst.halted_r;
    assign instr_undef = gb_inst.cpu_inst.control_inst.is_undef;
    assign last_pc     = gb_inst.cpu_inst.control_inst.instr_pc_r;
    assign last_opcode = gb_inst.cpu_inst.control_inst.instr_r;
    assign last_op1    = gb_inst.cpu_inst.control_inst.operand0_r;
    assign last_op2    = gb_inst.cpu_inst.control_inst.operand1_r;

    assign we      = gb_inst.we;
    assign address = gb_inst.address;
    assign wdata   = gb_inst.wdata;

    always @(posedge clk) begin
        if (nreset && instr_undef & ~halted) begin
            $display($sformatf("[%0t] %X: Undefined opcode %X | [%X | %X]", $time(), last_pc, last_opcode, last_op1, last_op2));
            $fatal(0);
            $finish();
        end
        if (nreset && we) begin
            $display($sformatf("[%0t] Write: [%X] <= %X", $time(), address, wdata));
        end
    end

endmodule : tb_top