题
我想创建一个地址解码器,该解码器在更改选择器的位和解码输出信号的位数时可以使用,该解码器足够灵活。
因此,与其具有看起来像这样的静态(固定输入/输出大小)解码器:
entity Address_Decoder is
Generic
(
C_INPUT_SIZE: integer := 2
);
Port
(
input : in STD_LOGIC_VECTOR (C_INPUT_SIZE-1 downto 0);
output : out STD_LOGIC_VECTOR ((2**C_INPUT_SIZE)-1 downto 0);
clk : in STD_LOGIC;
rst : in STD_LOGIC
);
end Address_Decoder;
architecture Behavioral of Address_Decoder is
begin
process(clk)
begin
if rising_edge(clk) then
if (rst = '1') then
output <= "0000";
else
case <input> is
when "00" => <output> <= "0001";
when "01" => <output> <= "0010";
when "10" => <output> <= "0100";
when "11" => <output> <= "1000";
when others => <output> <= "0000";
end case;
end if;
end if;
end process;
end Behavioral;
具有更灵活/一般的东西,看起来像这样:
entity Address_Decoder is
Generic
(
C_INPUT_SIZE: integer := 2
);
Port
(
input : in STD_LOGIC_VECTOR (C_INPUT_SIZE-1 downto 0);
output : out STD_LOGIC_VECTOR ((2**C_INPUT_SIZE)-1 downto 0);
clk : in STD_LOGIC;
rst : in STD_LOGIC
);
end Address_Decoder;
architecture Behavioral of Address_Decoder is
begin
DECODE_PROC:
process (clk)
begin
if(rising_edge(clk)) then
if ( rst = '1') then
output <= conv_std_logic_vector(0, output'length);
else
case (input) is
for i in 0 to (2**C_INPUT_SIZE)-1 generate
begin
when (i = conv_integer(input)) => output <= conv_std_logic_vector((i*2), output'length);
end generate;
when others => output <= conv_std_logic_vector(0, output'length);
end case;
end if;
end if;
end process;
end Behavioral;
我知道此代码无效,并且“何时”测试用例必须是常数,并且我不能在类似的案例语句之间使用for-for-enerate,但是它表明了我所追求的是什么:一个实体足够聪明,可以满足我的需求。
我一直在尝试在没有太大成功的情况下找到一个优雅的解决方案,因此,我愿意接受任何建议。
预先感谢埃里克
解决方案
显然,您希望输入是应设置的输出位的索引。
那样写。类似(假设来自numeric_std的类型):
output <= (others => '0'); -- default
output(to_integer(input)) <= '1';
其他提示
我总是发现,当您只循环每一位时,这种事情就更容易遵循,所以类似:
if ( rst = '1') then
output <= (others=>'0');
else
for i in 0 to (2**C_INPUT_SIZE)-1 generate
begin
if (i = conv_integer(input)) then
output(i) <= '1';
else
output(i) <= '0';
end if;
end generate;
end if;
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