书上的一段FIFO的代码，越看越不对劲....

只看该作者 · 2009-5-7 10:05

module FIFO(clk, reset_n, data_in, read_n, write_n, data_out, full, empty);
    input             clk;
    input             reset_n;
    input  [7:0]     data_in;
    input             read_n;
    input             write_n;
    output [7:0]     data_out;
    output             full;
    output             empty;

    wire                clk;
     wire                reset_n;
     wire    [7:0]        data_in;
     wire                read_n;
     wire                write_n;
     wire                full;
     wire                empty;
     reg    [7:0]        data_out;

     reg[7:0]    fifo_mem[15:0];  //fifo存储体
     reg[3:0]    counter;        //计数器，表示fifo用了多少
     reg[3:0]   rd_pointer; //fifo读指针
     reg[3:0]   wr_pointer;    //写指针

     //满空状态标志
     assign #`del full=(counter==16)?1'b1:1'b0;
     assign #`del empty=(counter==0)?1'b1:1'b0;

     //复位操作
     always@(reset_n)
     begin
         if(~reset_n)
            begin
            #`del;
            assign rd_pointer=4'b0;
            assign wr_pointer=4'b0;
            end
        else
            begin
            #`del;
            deassign rd_pointer;
            deassign wr_pointer;
            deassign counter;
            end
    end

    //计数，读写功能
    always@(posedge clk)
    begin
    //读操作数，计数器递减
        if(write_n）？？？这里为何只判断写使能无效就将计数器减1
            begin
            counter<=#`del counter-1;
            end
          data_out<=#`del fifo_mem[rd_pointer];
    //如果读指针指向末尾，则返回
        if(rd_pointer==14) ？？？rd_pointer等于15时才复位吧
             rd_pointer<=#`del 4'b0;
        else
            rd_pointer<=#del rd_pointer+1;

        if(~write_n)
            begin
            //检查是否溢出
            if(counter>=15)
                begin
                $display("\nerror at time %0t",$time);
                $display("fifo underflow\n");
                $stop
                end
            //写操作数，计数器加1
            if(read_n)  ？？？这里为何只判断读使能无效就将计数器加1

                begin
                counter<=#`del counter+1;
                end

            fifo_mem[wr_pointer]<=#`del data_in;
            //如果写指针指向末尾，则返回
            if(wr_pointer==14)
                wr_pointer<=#`del 4'b0;
            else
                wr_pointer<=#`del wr_pointer+1;
        end

    end
endmodule

好不容易手动把代码敲到ISE里面。觉得代码的逻辑太怪了，在读写标志递增时的条件判断感觉不对劲。