新手请指教

刚开始学FPGA，请各位F友多多指教。欢迎各位留言交流经验

我编了个小代码，仿真时出现竞争与冒险问题。有何解决办法不？高手一般是如何处理竞争与冒险的
library ieee;
        use ieee.std_logic_1164.all;
        use ieee.std_logic_unsigned.all;
--------------------------------------------------------
entity myFullAdder4 is
        port(a,b:in std_logic_vector(3 downto 0);
                c0:in std_logic;
                c4ut std_logic;
                sut std_logic_vector(3 downto 0));
end myFullAdder4;
--------------------------------------------------------
architecture behavior of myFullAdder4 is
        signal cc:std_logic_vector(3 downto 0);
        signal ss:std_logic_vector(4 downto 0):="00000";
begin
        cc<=(0=>c0,others=>'0');
        ss<=('0'&a)+('0'&b)+('0'&cc);
        s<=a + b + cc;
        c4<=ss(4);
end behavior;