Question

我是VHDL的新手。在我的一个任务中，我需要使用VHDL在State Table方法中实现状态机。所以我为architechture实体编写了以下代码：

X，Y是输入位，基本上这是一个moore机器，它接受两个输入并输出一位。

   architecture Table of SM1_2 is
  type StateTable is array(integer range<>,bit range<>,bit range<>) of integer;
  type OutTable is array(integer range<>) of bit;
  signal State,NextState : integer := 0;
  constant ST: StateTable(0 to 3,'0' to '1','0' to '1'):=
    ((3,0,1,0),(2,0,1,1),(3,0,1,1),(2,0,1,0));
  constant OT: OutTable(0 to 3):=
  ('0','1','1','0');
begin                               --Concurrent Statements
  NextState <= ST(State,X,Y);       --Next state from state table
  Z <= OT(State);

ModelSim报告错误：Integer literal 3 is not of type sub-array #3 of StateTable.

我已广泛搜索，但无法为此找到解决方案。如何在VHDL中使用多维数组？

Answer 1

StateTable类型被声明为integer类型的多维数组：

type StateTable is array(integer range<>,bit range<>,bit range<>) of integer;

从此类型创建的常量将分配一个不具有所需级别的数组：

constant ST : StateTable(0 to 3,'0' to '1','0' to '1') := ( (3,0,1,0), ...

因此尝试在常量值中添加级别，例如：

constant ST: StateTable(0 to 3,'0' to '1','0' to '1'):=
  (((3, 0), (1, 0)), 
   ((2, 0), (1, 1)), 
   ((3, 0), (1, 1)), 
   ((2, 0), (1, 0)));

创建常量时可以使用索引值，以便更清楚地将值分配给数组中的不同元素：

constant ST: StateTable(0 to 3,'0' to '1','0' to '1'):=
  (0 => ('0' => ('0' => 3, '1' => 0),
         '1' => ('0' => 1, '1' => 0)),
   1 => ('0' => ('0' => 2, '1' => 0),
         '1' => ('0' => 1, '1' => 1)),
   2 => ('0' => ('0' => 3, '1' => 0),
         '1' => ('0' => 1, '1' => 1)),
   3 => ('0' => ('0' => 2, '1' => 0),
         '1' => ('0' => 1, '1' => 0)));

Answer 2

您还可以使用嵌套数组来构建状态表：

constant state_cnt : positive := 4;
type t_inputtable is array (bit range <>, bit range <>) of natural range 0 to state_cnt-1;
type_t_statetable is array (natural range 0 to state_cnt-1) of t_inputtable;

constant statetable is t_statetable := (
--state   X,   Y   next state
  0 => (('0', '0') => 0,
        ('0', '1') => 1,
        ('1', '0') => 2,
        others => 0),
  1 => (('0', '0') => 0,
        ('0', '1') => 3,
        ('1', '0') => 2,
        others => 1),
  -- ...
  );

 nextState <= statetable(State)(X, Y);

我希望在键入这一行时没有错您还可以实现outputrecord：

type t_outputtable is record
  next : natural range 0 to state_cnt-1;
  O1 : bit;
  O2 : bit;
end record;
type t_inputtable is array (bit range <>, bit range <>) of t_outputtable;
type_t_statetable is array (natural range 0 to state_cnt-1) of t_inputtable;

nextState <= statetable(State)(X, Y).next;
Output1 <= statetable(State)(X, Y).O1;

多输入状态表方法

2 个答案: