这是我经常遇到的一个问题——希望有人能向我解释正确的思考方式!
我基本上可以将我的问题简化为:我有一个带有 input p_in
、 outputp_out
和 clock的模块clk
。功能是每当in
变低时 -out
应该产生一个持续时间为一个时钟周期的高脉冲;并且这个“负边缘检测器”被实现为具有四种状态的 FSM reset
:wt_in_lo
(等待输入低);sample_signal
(在检测到输入变为零时,在输出上生成高信号);wt_in_hi
(等待输入高电平,在采样信号被提升后)。
代码包含在下面,isim
模拟器中的结果是这样的(这是行为模拟,所以不应该有任何特定于平台的翻译影响):
基本上,状态确实会按照我的预期发生变化 - 第一个时钟位姿,FSM 识别in
为低电平,因此它转换为sample_signal
; 第二个时钟,我们处于sample_signal
状态。
- 但是,这是我的问题 - 我希望
out
一旦sample_signal
进入状态(或者至少,这就是我想要实现的目标),它就会变高;然而,在进入下一个状态 ( )之前out
不会执行高脉冲!wt_in_hi
然后我通常会尝试围绕这个进行编码(即out
在同步 fsm 部分中设置,这可能是一个坏主意) - 最终混淆了合成器和我自己:)
所以,简而言之 - 我是否有可能在out
进入第二个状态后立即收到一个信号(以及在第二个状态的持续时间内);什么是正确的编码方式?
非常感谢您的任何答案,
干杯!
编码:
-- file: fsm_react_test_twb.vhd
---------------
-- single file testbench examples - see also;
-- http://www.cs.umbc.edu/portal/help/VHDL/samples/samples.shtml
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;
-- NEVER call port pins "in"; "out": ERROR:HDLCompiler:806 'Syntax error near "in"'!
ENTITY negedgeDetector IS
PORT (
clk: IN STD_LOGIC;
p_in : IN STD_LOGIC;
p_out: OUT STD_LOGIC
);
END negedgeDetector;
ARCHITECTURE structure OF negedgeDetector IS
-- 'dummy signals' - registers
SIGNAL w_in : STD_LOGIC := 'Z';
SIGNAL w_out : STD_LOGIC := 'Z';
-- fsm states
TYPE states_ned IS -- ned: negedgeDetector
(
ned_reset,
ned_wt_in_lo, -- wait for in active low
ned_sample_signal, -- signal for sampling
ned_wt_in_hi -- wait for in active hi
);
-- init fsm state vars
SIGNAL state_ned, next_state_ned: states_ned := ned_reset;
-- implementation:
BEGIN
-- assign 'wire' / registers
w_in <= p_in;
p_out <= w_out;
-- STATE MACHINES CODE =========
sm_ned: PROCESS(state_ned, w_in) -- combinatorial process part
BEGIN
CASE state_ned IS
WHEN ned_reset =>
next_state_ned <= ned_wt_in_lo;
WHEN ned_wt_in_lo =>
IF w_in = '0' THEN
next_state_ned <= ned_sample_signal;
ELSE
next_state_ned <= ned_wt_in_lo;
END IF;
WHEN ned_sample_signal =>
next_state_ned <= ned_wt_in_hi;
WHEN ned_wt_in_hi =>
IF w_in = '0' THEN
next_state_ned <= ned_wt_in_lo;
ELSE
next_state_ned <= ned_wt_in_hi;
END IF;
END CASE;
END PROCESS sm_ned;
out_sm_ned: PROCESS(clk) -- synchronous process part --
BEGIN
IF (rising_edge(clk)) THEN -- returns only valid transitions;
IF state_ned = ned_sample_signal THEN
-- signal for sampling
w_out <= '1';
ELSE
w_out <= '0';
END IF;
state_ned <= next_state_ned;
END IF;
END PROCESS out_sm_ned;
-- END STATE MACHINES CODE =====
END structure; -- ARCHITECTURE
-- #########################
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;
ENTITY fsm_react_test_twb IS
END fsm_react_test_twb;
ARCHITECTURE testbench_arch OF fsm_react_test_twb IS
COMPONENT negedgeDetector
PORT(
clk: IN STD_LOGIC;
p_in : IN STD_LOGIC;
p_out: OUT STD_LOGIC
);
END COMPONENT;
-- 'wires'
SIGNAL wCLK : std_logic := '0';
SIGNAL wIN : std_logic := 'Z';
SIGNAL wOUT : std_logic := 'Z';
-- clock parameters
constant PERIODN : natural := 20; -- can be real := 20.0;
constant PERIOD : time := PERIODN * 1 ns;
constant DUTY_CYCLE : real := 0.5;
constant OFFSET : time := 100 ns;
-- implementation of workbench
BEGIN
-- instances of components, and their wiring (port maps)...
UUT : negedgeDetector -- VHDL
PORT MAP(
clk => wCLK,
p_in => wIN,
p_out => wOUT
);
-- PROCESSES (STATE MACHINES) CODE =========
-- clock process for generating CLK
clocker: PROCESS
BEGIN
WAIT for OFFSET;
CLOCK_LOOP : LOOP
wCLK <= '0';
WAIT FOR (PERIOD - (PERIOD * DUTY_CYCLE));
wCLK <= '1';
WAIT FOR (PERIOD * DUTY_CYCLE);
END LOOP CLOCK_LOOP;
END PROCESS clocker;
simulator: PROCESS
BEGIN
WAIT for OFFSET;
WAIT for 10 ns;
-- take 'in' low - out should detect it with a pulse
wIN <= '0';
WAIT for 50 ns;
-- take 'in' high - no out
wIN <= '1';
WAIT for 50 ns;
-- repeat
wIN <= '0';
WAIT for 50 ns;
wIN <= '1';
WAIT for 50 ns;
-- hold
WAIT;
END PROCESS simulator;
-- END PROCESSES (STATE MACHINES) CODE =====
END testbench_arch; -- ARCHITECTURE
-----------------------
-- call with (Xilinx ISE WebPack 13.2 tools):
-- # note: -tclbatch (isim script) _needs_ -view (*.wcfg) to run! (empty *.wcfg ok)
-- # must use isim script to run at start (and setup view)..
-- # first run:
-- echo 'vhdl work "fsm_react_test_twb.vhd"' > fsm_react_test_twb.prj
-- touch fsm_react_test_twb.wcfg
-- echo -e "wave add {/fsm_react_test_twb/wclk}\nwave add {/fsm_react_test_twb/win}\nwave add {/fsm_react_test_twb/wout}\nwave add {/fsm_react_test_twb/UUT/state_ned}\nwave add {/fsm_react_test_twb/UUT/next_state_ned}\nrun 500 ns\n" > fsm_react_test_twb.isim
-- # build sim and run:
-- fuse -o fsm_react_test_twb.exe -prj fsm_react_test_twb.prj work.fsm_react_test_twb
-- ./fsm_react_test_twb.exe -gui -tclbatch fsm_react_test_twb.isim -view fsm_react_test_twb.wcfg