题解 | #游戏机计费程序#

module game_count(
    input rst_n, 
    input clk, 
    input [9:0]money,
    input set,
    input boost,
    output reg [9:0]remain,
    output reg yellow,
    output reg red
    );
    reg valid;

    // 费用
    always @(posedge clk or negedge rst_n) begin
        if (!rst_n) begin
            remain <= 0;
            valid <= 0;
        end else begin
            valid <= 1;
            if (set) begin
                remain <= remain + money;
            end
            if (valid && !set) begin
                if (!boost) begin
                    remain <= remain < 1 ? remain : remain - 1;
                end else begin
                    remain <= remain < 2 ? remain : remain - 2;
                end
            end
        end
    end

    // 亮灯
    always @(posedge clk or negedge rst_n) begin
        if (!rst_n) begin
            yellow <= 0;
            red <= 0;
        end else begin
            yellow <= remain < 10 && remain > 0;
            red <= !boost && remain < 1 || boost && remain < 2;
        end
    end

endmodule