7

module top;
wire [3:0] x_in;
wire y_out;
system_clk #50 clk1(x_in[0]);
system_clk #100 clk2(x_in[1]);
system_clk #200 clk3(x_in[2]);
system_clk #400 clk4(x_in[3]);
and4_rtl c1 (y_out, x_in);
endmodule


module and4_rtl(y_out, x_in);
input [0:3] x_in;
output y_out;
assign y_out = &x_in;
endmodule

module system_clk(clk);
parameter period=100;
output clk;
reg clk;
initial
clk=0;
always
#(period/2)clk=~clk;
always@(posedge clk)
if($time>1000)
#(period-1)
$stop;
endmodule