module vending_fsm
(
    input clk_i
    , input rst_i

    , input coin_put_i                  // 1-cycle tick
    , input [7:0] coin_sum_bi

    , input select_good_i               // 1-cycle tick
    , input [7:0] select_good_num_bi
    , input [31:0] select_good_cost_bi

    , input cancel_i                    // 1-cycle tick

    , output logic give_order_o                 // 1-cycle tick
    , output logic [7:0]  give_order_num_bo

    , output logic give_change_o                // 1-cycle tick
    , output logic [31:0] give_change_sum_bo
);

enum {IDLE, CREDIT, DELIIVERY, CHANGE} state, state_next;

logic [7:0] selected_good, selected_good_next;
logic [31:0] credit_accumulated, credit_accumulated_next;

// "sequential" always block for register assignment
always @(posedge clk_i)
    begin
    if (rst_i)
        begin
        state <= IDLE;
        selected_good <= 0;
        credit_accumulated <= 0;
        end
    else
        begin
        state <= state_next;
        selected_good <= selected_good_next;
        credit_accumulated <= credit_accumulated_next;
        end

    end

// "combinational" always block for next-state generation
always @*
    begin

    // Restoring current register values
    state_next = state;
    selected_good_next = selected_good;
    credit_accumulated_next = credit_accumulated;

    //...

    case (state_next)

    //...

        CREDIT:
            begin
            if (coin_put_i)
                begin
                credit_accumulated_next = credit_accumulated_next + coin_sum_bi;
                end
            else if (select_good_i)
                begin
                selected_good_next = select_good_num_bi;
                check_credit = credit_accumulated_next - select_good_cost_bi;
                if (check_credit < 0)
                    begin
                    state_next = CHANGE;
                    end
                else
                    begin
                    credit_accumulated_next <= check_credit;
                    state_next = DELIIVERY;
                    end
                end
            else if (cancel_i)
                begin
                state_next = CHANGE;
                end
            end


    //...

    end

endmodule // vending_fsm