哪位大虾帮忙找找这个状态机程序的错（VHDL）

library ieee;
use ieee.std_logic_1164.all;

entity moore2 is port(
  clk, rst:   in std_logic;
  id:     in std_logic_vector(3 downto 0);
  y:    out std_logic_vector(2 downto 0));
end moore2;

architecture archmoore2 of moore2 is
  signal state,next_state: std_logic_vector(2 downto 0);

constant state0: std_logic_vector(2 downto 0) := "000";
constant state1: std_logic_vector(2 downto 0) := "010";
constant state2: std_logic_vector(2 downto 0) := "011";
constant state3: std_logic_vector(2 downto 0) := "110";
constant state4: std_logic_vector(2 downto 0) := "111";
begin
a:process(clk,rst)
    begin
        if (rst='1') then
        state<=state0;
        elsif(clk'event and clk='1')then
        state<=next_state;
        end if;        
    end process    ;
b: process (state, rst)
  begin
      if (rst='1') then
        state <= state0;
      end if;
        case state is

          when state0 =>
              if id = x"3" then
                next_state <= state1;
              else
                next_state <= state0;
              end if;
          when state1 =>
              next_state <= state2;
          when state2 =>
              if id = x"7" then
                next_state <= state3;
              else
                next_state <= state2;
              end if;
          when state3 =>
              if id < x"7" then
                next_state <= state0;
              elsif id = x"9" then
                next_state <= state4;
              else
                next_state <= state3;
              end if;
          when state4 =>
              if id = x"b" then
                next_state <= state0;
              else
                next_state <= state4;
              end if;
          when others =>
              next_state <= state0;
        end case;

  end process;



y <= state(2 downto 0);
end archmoore2;

用quartus编译后的错误信息：
Error: Can't resolve multiple constant drivers for net "state[2]" at moore2.vhd(22)
Error: Constant driver at moore2.vhd(30)
Error: Can't elaborate top-level user hierarchy

我是新手请多指教

两个process中有相同变量的赋值吧。

谢谢喽！！！

把沿的变化放在elsif后也不好吧

两个process中有相同变量的赋值吧。