我正在用VHDL实现一个正交解码器,并提出了两种解决方案。VHDL正交解码器:顺序/组合逻辑
在方法1中,所有的逻辑都放在一个对时钟和复位敏感的进程中。 在Spartan-3A上,它使用四个片,七个FF和四个输入LUT。
代码1
architecture Behavioral of quadr_decoder is
signal chan_a_curr : std_logic;
signal chan_a_prev : std_logic;
signal chan_b_curr : std_logic;
signal chan_b_prev : std_logic;
begin
process (n_reset, clk_in) begin
if (n_reset = '0') then
-- initialize internal signals
chan_a_curr <= '0';
chan_a_prev <= '0';
chan_b_curr <= '0';
chan_b_prev <= '0';
-- initialize outputs
count_evt <= '0';
count_dir <= '0';
error_evt <= '0';
elsif (clk_in'event and clk_in = '1') then
-- keep delayed inputs
chan_a_prev <= chan_a_curr;
chan_b_prev <= chan_b_curr;
-- read current inputs
chan_a_curr <= chan_a;
chan_b_curr <= chan_b;
-- detect a count event
count_evt <= ((chan_a_prev xor chan_a_curr) xor
(chan_b_prev xor chan_b_curr));
-- determine count direction
count_dir <= (chan_a_curr xor chan_b_prev xor
count_mode);
-- detect error conditions
error_evt <= ((chan_a_prev xor chan_a_curr) and
(chan_b_prev xor chan_b_curr));
end if;
end process;
end Behavioral;
方法2拆分逻辑成单独的顺序和组合过程。它使用两个切片,四个FF和四个输入LUT。
代码2
architecture Behavioral of quadr_decoder is
signal chan_a_curr : std_logic;
signal chan_a_prev : std_logic;
signal chan_b_curr : std_logic;
signal chan_b_prev : std_logic;
begin
process (n_reset, clk_in) begin
if (n_reset = '0') then
-- initialize internal signals
chan_a_curr <= '0';
chan_a_prev <= '0';
chan_b_curr <= '0';
chan_b_prev <= '0';
elsif (clk_in'event and clk_in = '1') then
-- keep delayed inputs
chan_a_prev <= chan_a_curr;
chan_b_prev <= chan_b_curr;
-- read current inputs
chan_a_curr <= chan_a;
chan_b_curr <= chan_b;
end if;
end process;
process (chan_a_prev, chan_a_curr, chan_b_prev, chan_b_curr) begin
-- detect a count event
count_evt <= ((chan_a_prev xor chan_a_curr) xor
(chan_b_prev xor chan_b_curr));
-- determine count direction
count_dir <= (chan_a_curr xor chan_b_prev xor count_mode);
-- detect error conditions
error_evt <= ((chan_a_prev xor chan_a_curr) and
(chan_b_prev xor chan_b_curr));
end process;
end Behavioral;
当我模拟代码(行为),这两种结果已经很好了。但我不能相信这两种方法是同样有效的。 有人可以说明哪种方法比其他方法更受欢迎?