我正在用VHDL實現一個正交解碼器,並提出了兩種解決方案。VHDL正交解碼器:順序/組合邏輯
在方法1中,所有的邏輯都放在一個對時鐘和復位敏感的進程中。 在Spartan-3A上,它使用四個片,七個FF和四個輸入LUT。
代碼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拆分邏輯成單獨的順序和組合過程。它使用兩個切片,四個FF和四個輸入LUT。
代碼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;
當我模擬代碼(行爲),這兩種結果已經很好了。但我不能相信這兩種方法是同樣有效的。 有人可以說明哪種方法比其他方法更受歡迎?