我不断收到错误“Case 语句必须涵盖表达式的所有可能值”。我该如何解决这个问题？

Question

我在第 35 行得到了 case 语句必须涵盖表达式的所有可能值，“Case 显示计数器是”

如果您在代码中发现任何其他错误，请告诉我。

这是下面代码的键入版本

library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

use IEEE.STD_LOGIC_ARITH.ALL;

use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity SimonGame is

Port ( clk : in STD_LOGIC;

       rst : in STD_LOGIC;

       btn1, btn2, btn3, btn4 : in STD_LOGIC;

       hex_0, hex_1, hex_2 : out STD_LOGIC_VECTOR(6 downto 0));

end SimonGame;


architecture Behavioral of SimonGame is

signal sequence : STD_LOGIC_VECTOR(2 downto 0);

signal count : INTEGER := 0;

signal display_counter : INTEGER := 0;

signal correct_input : BOOLEAN := TRUE;

type Digit_State is (DISPLAY_SEQUENCE, AWAIT_INPUT);

signal state : Digit_State := DISPLAY_SEQUENCE;

begin
process(clk, rst)
begin
    if rst = '1' then
        sequence <= "001"; -- Initial sequence
        count <= 0;
        display_counter <= 0;
        state <= DISPLAY_SEQUENCE;
    elsif rising_edge(clk) then
        case state is
            when DISPLAY_SEQUENCE =>
                -- Display the sequence on hex_0 and hex_1
                case display_counter is
                    when 0 =>
                        hex_0 <= "0000001";
                        hex_1 <= "0000000";
                    when 1 =>
                        hex_0 <= "0001000";
                        hex_1 <= "0000000";
                    when 2 =>
                        hex_0 <= "0000100";
                        hex_1 <= "0000000";
                    when 3 =>
                        hex_0 <= "0000010";
                        hex_1 <= "0000000";
                    when 4 =>
                        hex_0 <= "0001000";
                        hex_1 <= "0000000";
                    when 5 =>
                        hex_0 <= "0000001";
                        hex_1 <= "0000000";
                        state <= AWAIT_INPUT;
                end case;

                if display_counter < 5 then
                    display_counter <= display_counter + 1;
                else
                    display_counter <= 0;
                    count <= count + 1;
                    sequence <= sequence(0) & sequence(2 downto 1); -- Shift the sequence
                end if;

            when AWAIT_INPUT =>
                -- Check button input against the sequence
                if btn1 = '1' then
                    correct_input <= (sequence = "001");
                elsif btn4 = '1' then
                    correct_input <= (sequence = "010");
                elsif btn3 = '1' then
                    correct_input <= (sequence = "100");
                elsif btn2 = '1' then
                    correct_input <= (sequence = "010");
                else
                    correct_input <= FALSE;
                end if;

                if correct_input then
                    state <= DISPLAY_SEQUENCE;
                end if;
        end case;
    end if;
end process;
end Behavioral;

Answer 1

case

语句必须始终涵盖变量可以采用的所有可能值。在你的情况下 0 <=

display_counter

<= 5 is covered, but what if

display_counter

小于 0 还是大于 5？您必须告诉您的程序在这些情况下该怎么做。总体结构如下：

case my_variable is
    when value1 =>
        -- do something for value1
    when value2 =>
        -- do something for value2
    when others =>
        -- default action when my_variable doesn't match any defined case
end case;