流水线之3个乘法器实现S=a*b*c*d

//流水线之3个乘法器实现S=abc*d

module cy4(input[3:0] a,b,c,d, 
           input vld_in,//输入有效指示信号
		   input clk,rst_n,
		   output reg[15:0] dout,
		   output reg vld_out//输出有效指示信号
		   );
reg vld_in_ff0;//中间缓存寄存器

always  @(posedge clk or negedge rst_n)
    if(rst_n==1'b0) dout <= 0;
	else dout <= a * b * c * d;

always  @(posedge clk or negedge rst_n)begin
    if(rst_n==1'b0)begin
        vld_out <= 0;
        vld_in_ff0 <= 0;
    end
    else  begin
        vld_in_ff0  <= vld_in;
        vld_out  <= vld_in_ff0;
    end
end
endmodule