VHDL中行为和数据流模型程序之间的混淆(Confusion between Behavioural and Dataflow model Programs in VHDL)

 我正在使用Douglas L Perry，第四版的教科书“VHDL：Programming By Example”。 他在第4页中给出了Dataflow编程模型的示例： 
 
 代码I： 
 
ENTITY mux IS
PORT ( a, b, c, d : IN BIT;
s0, s1 : IN BIT;
x, : OUT BIT);
END mux;
ARCHITECTURE dataflow OF mux IS
SIGNAL select : INTEGER;
BEGIN
select <= 0 WHEN s0 = ‘0’ AND s1 = ‘0’ ELSE
          1 WHEN s0 = ‘1’ AND s1 = ‘0’ ELSE
          2 WHEN s0 = ‘0’ AND s1 = ‘1’ ELSE
          3;
x <= a AFTER 0.5 NS WHEN select = 0 ELSE
     b AFTER 0.5 NS WHEN select = 1 ELSE
     c AFTER 0.5 NS WHEN select = 2 ELSE
     d AFTER 0.5 NS;
END dataflow;
 
 现在，在第17页， 代码II 
 
LIBRARY IEEE;
USE IEEE.std_logic_1164.ALL;
ENTITY mux4 IS
PORT ( i0, i1, i2, i3, a, b : IN std_logic;
PORT ( i0, i1, i2, i3, a, q : OUT std_logic);
END mux4;
ARCHITECTURE mux4 OF mux4 IS
SIGNAL sel: INTEGER;
BEGIN
WITH sel SELECT
q <= i0 AFTER 10 ns WHEN 0,
q <= i1 AFTER 10 ns WHEN 1,
q <= i2 AFTER 10 ns WHEN 2,
q <= i3 AFTER 10 ns WHEN 3,
q <= ‘X’ AFTER 10 ns WHEN OTHERS;
sel <= 0 WHEN a = ‘0’ AND b = ‘0’ ELSE
       1 WHEN a = ‘1’ AND b = ‘0’ ELSE
       2 WHEN a = ‘0’ AND b = ‘1’ ELSE
       3 WHEN a = ‘1’ AND b = ‘1’ ELSE
       4;
END mux4;
 
 根据同一本教科书，这应该是一种行为模型 。 除了变量名称的差异之外，我在这里看到的唯一主要区别是有一个额外的声明 
 
WITH sel SELECT
 
 在第二种情况下，和小的语法差异。 本守则II同时发布。 但是从互联网上的其他来源（如下所列），我已经看到行为模型应该是顺序的。 我应该相信哪一个？ 
 
 现在来自互联网的其他一些来源，这些模型的定义如下： 
 
 行为 - 电路被描述为使用过程内的顺序语句的I / O关系。 
 
 数据流 - 使用并发语句描述电路 
 
 - 圣何塞州立大学 
 
 行为 - 描述输出如何使用结构化语句从输入中获得。 
 
 数据流 - 描述数据如何流动。 
 
 - 阿克伦大学工程学院 
 
 在这里，我不明白结构化陈述的含义。 
 
 在行为级别，存在流程关键字 
 
 在数据流级别中，存在并发语句（<=） 
 
 
 这是在一个在线论坛上看到的。 
 
 行为模型是强制性的流程声明吗？ 
 
 代码I和II之间的实际差异是什么？ 据作者说，他们有不同的模型，数据流和行为。 我看不出这是怎么可能的。 我应该相信什么？ 
 
 最后，在佩里DL，第45页，46： 
 
LIBRARY IEEE;
USE IEEE.std_logic_1164ALL;
ENTITY mux IS
PORT (i0, i1, i2, i3, a, b : IN std_logic;
PORT (q : OUT std_logic);
END mux;
ARCHITECTURE better OF mux IS
BEGIN
PROCESS ( i0, i1, i2, i3, a, b )
VARIABLE muxval : INTEGER;
BEGIN
muxval := 0;
IF (a = ‘1’) THEN
muxval := muxval + 1;
END IF;
IF (b = ‘1’) THEN
muxval := muxval + 2;
END IF;
CASE muxval IS
WHEN 0 =>
q <= I0 AFTER 10 ns;
WHEN 1 =>
q <= I1 AFTER 10 ns;
WHEN 2 =>
q <= I2 AFTER 10 ns;
WHEN 3 =>
q <= I3 AFTER 10 ns;
WHEN OTHERS =>
NULL;
END CASE;
END PROCESS;
END better;
 
 这是MUX的顺序版本。 根据其他定义，这应该是行为，但作者没有这样说。 你能否清楚我对这些模型的困惑？ 

I'm using the textbook "VHDL: Programming By Example" by Douglas L Perry, Fourth Edition. He gave an example of the Dataflow programming model in page 4:
 
Code I:
 
ENTITY mux IS
PORT ( a, b, c, d : IN BIT;
s0, s1 : IN BIT;
x, : OUT BIT);
END mux;
ARCHITECTURE dataflow OF mux IS
SIGNAL select : INTEGER;
BEGIN
select <= 0 WHEN s0 = ‘0’ AND s1 = ‘0’ ELSE
          1 WHEN s0 = ‘1’ AND s1 = ‘0’ ELSE
          2 WHEN s0 = ‘0’ AND s1 = ‘1’ ELSE
          3;
x <= a AFTER 0.5 NS WHEN select = 0 ELSE
     b AFTER 0.5 NS WHEN select = 1 ELSE
     c AFTER 0.5 NS WHEN select = 2 ELSE
     d AFTER 0.5 NS;
END dataflow;
 
Now in page 17, Code II
 
LIBRARY IEEE;
USE IEEE.std_logic_1164.ALL;
ENTITY mux4 IS
PORT ( i0, i1, i2, i3, a, b : IN std_logic;
PORT ( i0, i1, i2, i3, a, q : OUT std_logic);
END mux4;
ARCHITECTURE mux4 OF mux4 IS
SIGNAL sel: INTEGER;
BEGIN
WITH sel SELECT
q <= i0 AFTER 10 ns WHEN 0,
q <= i1 AFTER 10 ns WHEN 1,
q <= i2 AFTER 10 ns WHEN 2,
q <= i3 AFTER 10 ns WHEN 3,
q <= ‘X’ AFTER 10 ns WHEN OTHERS;
sel <= 0 WHEN a = ‘0’ AND b = ‘0’ ELSE
       1 WHEN a = ‘1’ AND b = ‘0’ ELSE
       2 WHEN a = ‘0’ AND b = ‘1’ ELSE
       3 WHEN a = ‘1’ AND b = ‘1’ ELSE
       4;
END mux4;
 
This is supposed to be a behavioural model, as per the same textbook. Aside from the differences in variable name, the only major difference I see here is that there is an extra statement
 
WITH sel SELECT
 
in the second case, and small syntax differences. This Code II is concurrent. But from other sources in the internet(listed below), I've seen that a behavioural model is supposed to be sequential. Which one should I believe?
 
Now from some other sources of the internet, the definition of these models are as follows:
 
Behavioral – Circuit is described as an i/o relationship using sequential statements inside a process.
 
Dataflow – Circuit is described using concurrent statements
 
-San Jose State university
 
Behavioral – describes how the output is derived from the inputs using structured statements.
 
Dataflow – describes how the data flows.
 
-University of Akron College of Engineering
 
Here I do not understand what structured statements mean.
 
in Behaviour level, process keyword is present 
 
in dataflow level , concurrent statement (<=) is present 
 
 
This was seen in an online forum.
 
Is process statement compulsory for Behavioural model? 
 
What is the actual difference between codes I and II? According to the author, they have different models, dataflow and behavioural. I cannot see how this is possible. What should I believe? 
 
Lastly, in Perry D L, Page 45, 46:
 
LIBRARY IEEE;
USE IEEE.std_logic_1164ALL;
ENTITY mux IS
PORT (i0, i1, i2, i3, a, b : IN std_logic;
PORT (q : OUT std_logic);
END mux;
ARCHITECTURE better OF mux IS
BEGIN
PROCESS ( i0, i1, i2, i3, a, b )
VARIABLE muxval : INTEGER;
BEGIN
muxval := 0;
IF (a = ‘1’) THEN
muxval := muxval + 1;
END IF;
IF (b = ‘1’) THEN
muxval := muxval + 2;
END IF;
CASE muxval IS
WHEN 0 =>
q <= I0 AFTER 10 ns;
WHEN 1 =>
q <= I1 AFTER 10 ns;
WHEN 2 =>
q <= I2 AFTER 10 ns;
WHEN 3 =>
q <= I3 AFTER 10 ns;
WHEN OTHERS =>
NULL;
END CASE;
END PROCESS;
END better;
 
This is a sequential version of MUX. According to the other definitions, this is supposed to be behavioural, but the author does not state so. Could you clear up my confusion regarding these models?

原文：https://stackoverflow.com/questions/18682019