请教个问题 关于Warning: Output pins are stuck at VCC or GND

总出现警告：Warning: Output pins are stuck at VCC or GND                          
Warning (13410): Pin "L" is stuck at GND
程序如下
//test button and led
module button(E,L,clk);  //capital
output L;
input E,clk;
reg sig=1'd0,count=11'd0,LED=1'd0;  

always@ (negedge E)
sig <= 1'd1;

always@ (posedge clk) begin
if (sig == 1'd1)
        if (count == 11'd1999) begin
        sig <= 1'd0;
        count <= 11'd0;
        LED <= 1'd1;
        end
        else count <= count + 1'd1;
end  
assign L = LED;
endmodule

显示警告：Warning: Output pins are stuck at VCC or GND
        Warning (13410): Pin "L" is stuck at GND
      Warning: Design contains 2 input pin(s) that do not drive logic
        Warning (15610): No output dependent on input pin "E"
        Warning (15610): No output dependent on input pin "clk"
Warning: Following 1 pins have nothing, GND, or VCC driving datain port -- changes to this connectivity may change fitting results
        Info: Pin L has GND driving its datain port

额，显示有人回复，怎么看不到呢