基于FPGA的图像处理（五）状态机

        使用FPGA实现各种算法时，状态机是很常用的方法，在SysGen中有两种非常简便的方法构建状态机，一是使用Mcode，以switch-case语句轻松实现，二是使用SysGen自带状态机模块。

     状态机

假设我们要从01序列中检测出1011序列，则状态机模型如下

Next State Matrix：[0 1; 2 1; 0 3; 2 1]

Output Matrix ： [0 0; 0 0; 0 0; 0 1]

一、使用Mcode实现

上一篇博客讲解了在Sysgen中Mcode的限制能力，这里直接使用

构建模型如下：

Singal From Workspace用于产生一个01序列，作为输入信号。

gatwayIn将数据类型转化为UFix_1_0

添加Mcode函数stateMcode.m

function [nextState, matched] = stateMcode(currentState, din)
% This is the update function for detecting a pattern of 1011
% This function represents a stateless and combination logic block.
% The output nextState should be to a register, and the output
% of the register should be fed back to the input currentState.
% Because the state register block has a feed back connection, in
% order to propagate the port prototypes automatically, the prototype
% of nextState should be determined only by constants or through
% an explicity xfix() call.

  seen_none = 0; % initial state, if input is 1, switch to seen_1
  seen_1 = 1;    % first 1 has been seen, if input is 0, switch
                 % seen_10
  seen_10 = 2;   % 10 has been detected, if input is 1, switch to
                 % seen_1011
  seen_101 = 3;  % now 101 is detected, is input is 1, 1011 is
                 % detected and the FSM switches to seen_1

  % the default value of matched is false
  matched = false;

  switch currentState
   case seen_none
    if din==1
      nextState = seen_1;
    else
      nextState = seen_10;
    end
   case seen_1 % seen first 1
    if din==1
      nextState = seen_1;
    else
      nextState = seen_10;
    end
   case seen_10 % seen 10
    if din==1
      nextState = seen_101;
    else
      % no part of sequence seen, go to seen_none
      nextState = seen_none;
    end
   case seen_101
    if din==1
      nextState = seen_1;
      matched = true;
    else
      nextState = seen_10;
      matched = false;
    end
   otherwise
    % if nextState is not assigned outside the switch statement,
    % an otherwise statment is required
    nextState = seen_none;
  end

Scope效果如图：

二、使用Mealy State Machine模块实现

构建模型：

设置Mealy State Machine参数，就是状态机的参数

仿真结果如下：

在进行FPGA图像处理时，经常会用到状态机，这几天刚学习过，记录一下，其实使用Verilog直接实现也不是很难，只是会比SysGen稍微麻烦一些，修改起来也会花费更多的时间。

Model Based Design 在Xilinx 的工具中逐渐得到加强，相信以后会更加的方便。