COMMUNICATION BETWEEN PC AND ARDUINO YUN VIA WIFI:
The core codes of setting SSHD is from eecharlie. Please see：
https://forum.processing.org/two/discussion/328/connecting-processing-to-arduino-yun-yun

这里稍微解释以下核心的processing code
第一步，在你的processing项目中包含可以利用的SSH协议包，比如这里使用的JSch。关于JSch的使用可以参考：

http://www.jcraft.com/jsch/

第二步，利用SSH成功登陆Arduino Yun的根服务器，所以需要在写processing code时设定：

String user ="root";
String password ="******";
String host ="192.168.240.1";int port=22;

如果你没有更改Arduino Yun的根服务器地址，那么默认地址应该是192.168.240.1，不论怎样，搞清楚你的host
第三步，按照协议写好输入流与输出流的code：

Session session = jsch.getSession(user, host, port);
session.setPassword(password);
//设定user, host port和密码
session.setConfig("StrictHostKeyChecking","no");
// less than maximally secure
session.connect();
//尝试连接根服务器    
System.out.println("Connection established.");
Channel channel = session.openChannel("exec");
channel.setInputStream(null);
((ChannelExec) channel).setCommand("telnet localhost 6571");
//连接成功后用telnet命令调出传输数据     channel.connect();

下面主要是如何将接受的数据流转换成可应用的double型数据的问题。
注意一下，这里考虑的是在Arduino Yun里使用Console.printl(Ver)直接传输数据变量。如果你在Arduino Yun里就建立好传输规则，规定好每个变量传输的格式，那么就可以在processing里规定好每个流有多少字符，每个字符的作用，这样可以大幅度提升传输效率。这里所给出的是在Arduino Yun里没有传输规则的情形，所以每个变量的字符长度不一样，这样每次循环只能设定为每个流有一个字符，这样就出现了接受不同步的现象。同样，下面也给出了解决方案。

Results and further input will be handled by the streams.
Each loop transfers one byte data. Each charactor occupied one byte.
If the Arduino Yun sends numbers, for example -5.63, to this clinet, the complete stream is following:
(The data from Arduino alwasys keeps two decimal places like -5.63, 4.57, 18.71 if you use fuction Console.println().)
Loop count |First Loop|Second Loop|Third Loop|Fourth Loop|Fifth Loop|Sixth Loop|Seventh Loop|
Charactors |   empty  |    -      |    5     |     .     |    6     |     3    |    '\n'    |
The ideas to transfer the stream to float numbers are following:
1. Starting after receiving '\n'.
2. Receiving all numbers and put them into one array.
3. Transfer elements in array to a decimal number.
4. Determining the sign.

DATA TRANSFER SYNCHRONIZATION
In Arduino Yun, the program loop time is approx 110ms.  
在Arduino Yun里精确设定好循环时间。
The client needs receive 7 data and each data needs at least 7 cycles.
设定好需要传输的变量个数。
So, to keep the synchronism for receiving and sending, the client program needs finish 49 cycles in 110ms.
The defult value of framerate for processing is 60/s. Here, the framerate should be larger than 445/s.

计算好processing的framerate。

ArduinoYunToProcessing.pdf