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 <head><title>lwIP - A Lightweight TCP/IP Stack - OS vs non-OS</title></head>


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 <center><h1>lwIP - A Lightweight TCP/IP Stack</h1></center>
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 <a href="index.html">Introduction</a>

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 <hr>
 </td></tr>
 <tr>
 <td><center><h2>OS vs non-OS</h2></center>
 </td></tr></table>

 <table width="640" border="0" cellpadding="0"
 cellspacing="0"><tr>
 <td width="50">
 &nbsp;
 </td>
 <td bgcolor="white" width="540">

 <h2>Using lwIP with or without an operating system</h2>

 <p align="justify">
 There has been a few questions about how lwIP can be used in a
 standalone environment (i.e., an environment without a multi-threaded
 operating system) lately. The purpose of this document is to describe
 how lwIP is designed to be used with and without a multi-threaded
 operating system.
 </p>

 <center><img src="os.png"></center>

 <h3>The lwIP single-threaded core</h3>
 <p align="justify">
 The core of lwIP consists of the actual implementations of the IP,
 ICMP, UDP, and TCP protocols, as well as the support functions such as
 buffer and memory management. The core components are the only ones
 that are needed when lwIP is to be run in a single-threaded (non-OS)
 environment.
 </p>
 <p align="justify">
 The core components can be viewed as a software library which has the
 following interface:
 </p>
 <ul>
 <li><tt>ip_input(pbuf, netif)</tt>: Takes an IP packet and the incoming network
 interface as arguments and does the TCP/IP processing for the packet.
 <li><tt>tcp_tmr()</tt>: Should be called every 100 ms. Does all TCP
 timer processing such as doing retransmissions.
 </ul>
 <p align="justify">
 Because none of the core functions ever needs to block when run in a
 single-threaded environment, the <tt>sys_arch</tt> (the operating
 system abstraction layer) does not need to implement locking
 semaphores or mailboxes. In future versions of lwIP, the dependancy of
 the <tt>sys_arch</tt> will be removed in the single-threaded case.
 </p>
 <p align="justify">
 A simple main loop for a single-threaded system might look
 like this:
 </p>
 <pre>
   while(1) {
     if(poll_driver(netif) == PACKET_READY) {
       pbuf = get_packet(netif);
       ip_input(pbuf, netif);
     }

     if(clock() - last_time == 100 * CLOCK_MS) {
       tcp_tmr();
       last_time = clock();
     }
   }
 </pre>

 <h3>lwIP in a multi-threaded system</h3>
 <p align="justify">
 lwIP is designed to be able to be run in a multi-threaded system with
 applications running in concurrent threads. The model used in this
 case is that all TCP/IP processing is done in a single thread. The
 application thread communicate with the TCP/IP thread using the
 sequential API.
 </p>

 <center><img src="threads.png"></center>

 <p align="justify">
 The inter-thread communication is implemented in the two files
 <tt>api_lib.c</tt> and <tt>api_msg.c</tt>. The former contains the
 functions used by the application programs and the latter implements
 the TCP/IP stack interface. A third file, <tt>tcpip.c</tt>, handles
 incoming packets and timer events as described in the previous
 section.
 </p>

 <p align="justify">
 When run in a multi-threaded environment, incoming packets are handled
 by the function <tt>tcpip_input()</tt>, which takes the same arguments
 as the <tt>ip_input()</tt> function. The difference between the two
 functions is that the <tt>tcpip_input()</tt> function does not process
 the incoming packet immediately. It merely puts the packet on a queue
 which later is drained by the TCP/IP thread.
 </p>

 <p align="justify">
 When being run in a multi-threaded system, timer events are taken care
 of internally in <tt>tcpip.c</tt>.
 </p>

 <p align="right">
 <font size="-1"><i>
 $Date: 2002/10/19 13:00:03 $
 </i></font>
 </p>


 </td>
 <td width="50">
 &nbsp;
 </td>
 </tr></table>

 <table width="640" border="0" cellpadding="0"
 cellspacing="0">
 <tr><td align="center">

 <hr>


 <a href="index.html">Introduction</a>

 |

 <a href="news.html">News</a>

 |

 <a href="documentation.html">Documentation</a>

 |

 <a href="mailinglist.html">Mailing list</a>

 |

 <a href="changelog.html">Changelog</a>

 |

 <a href="download.html">Download</a>

 |

 <a href="links.html">Links</a>


 <hr>

 </td></tr><tr>
 <td>
 <div align="right">
 <a href="http://www.sics.se/~adam/">Adam Dunkels</a></div>
 </td>
 </tr>
 </table>

 </body>
 </html>












	<html>
	<head><title>lwIP - A Lightweight TCP/IP Stack - OS vs non-OS</title></head>


	<body bgcolor="white">

	<table width="640" border="0" cellpadding="0"
	cellspacing="0">
	<tr><td>
	<center><h1>lwIP - A Lightweight TCP/IP Stack</h1></center>
	</td></tr></table>


	<table width="640" border="0" cellpadding="0"
	cellspacing="0">
	<tr><td align="center">
	<hr>




	<a href="index.html">Introduction</a>

	\|

	<a href="news.html">News</a>

	\|

	<a href="documentation.html">Documentation</a>

	\|

	<a href="mailinglist.html">Mailing list</a>

	\|

	<a href="changelog.html">Changelog</a>

	\|

	<a href="download.html">Download</a>

	\|

	<a href="links.html">Links</a>



	<hr>
	</td></tr>
	<tr>
	<td><center><h2>OS vs non-OS</h2></center>
	</td></tr></table>

	<table width="640" border="0" cellpadding="0"
	cellspacing="0"><tr>
	<td width="50">

	</td>
	<td bgcolor="white" width="540">

	<h2>Using lwIP with or without an operating system</h2>

	<p align="justify">
	There has been a few questions about how lwIP can be used in a
	standalone environment (i.e., an environment without a multi-threaded
	operating system) lately. The purpose of this document is to describe
	how lwIP is designed to be used with and without a multi-threaded
	operating system.
	</p>

	<center><img src="os.png"></center>

	<h3>The lwIP single-threaded core</h3>
	<p align="justify">
	The core of lwIP consists of the actual implementations of the IP,
	ICMP, UDP, and TCP protocols, as well as the support functions such as
	buffer and memory management. The core components are the only ones
	that are needed when lwIP is to be run in a single-threaded (non-OS)
	environment.
	</p>
	<p align="justify">
	The core components can be viewed as a software library which has the
	following interface:
	</p>
	<ul>
	<li><tt>ip_input(pbuf, netif)</tt>: Takes an IP packet and the incoming network
	interface as arguments and does the TCP/IP processing for the packet.
	<li><tt>tcp_tmr()</tt>: Should be called every 100 ms. Does all TCP
	timer processing such as doing retransmissions.
	</ul>
	<p align="justify">
	Because none of the core functions ever needs to block when run in a
	single-threaded environment, the <tt>sys_arch</tt> (the operating
	system abstraction layer) does not need to implement locking
	semaphores or mailboxes. In future versions of lwIP, the dependancy of
	the <tt>sys_arch</tt> will be removed in the single-threaded case.
	</p>
	<p align="justify">
	A simple main loop for a single-threaded system might look
	like this:
	</p>
	<pre>
	while(1) {
	if(poll_driver(netif) == PACKET_READY) {
	pbuf = get_packet(netif);
	ip_input(pbuf, netif);
	}

	if(clock() - last_time == 100 * CLOCK_MS) {
	tcp_tmr();
	last_time = clock();
	}
	}
	</pre>

	<h3>lwIP in a multi-threaded system</h3>
	<p align="justify">
	lwIP is designed to be able to be run in a multi-threaded system with
	applications running in concurrent threads. The model used in this
	case is that all TCP/IP processing is done in a single thread. The
	application thread communicate with the TCP/IP thread using the
	sequential API.
	</p>

	<center><img src="threads.png"></center>

	<p align="justify">
	The inter-thread communication is implemented in the two files
	<tt>api_lib.c</tt> and <tt>api_msg.c</tt>. The former contains the
	functions used by the application programs and the latter implements
	the TCP/IP stack interface. A third file, <tt>tcpip.c</tt>, handles
	incoming packets and timer events as described in the previous
	section.
	</p>

	<p align="justify">
	When run in a multi-threaded environment, incoming packets are handled
	by the function <tt>tcpip_input()</tt>, which takes the same arguments
	as the <tt>ip_input()</tt> function. The difference between the two
	functions is that the <tt>tcpip_input()</tt> function does not process
	the incoming packet immediately. It merely puts the packet on a queue
	which later is drained by the TCP/IP thread.
	</p>

	<p align="justify">
	When being run in a multi-threaded system, timer events are taken care
	of internally in <tt>tcpip.c</tt>.
	</p>

	<p align="right">
	<font size="-1"><i>
	$Date: 2002/10/19 13:00:03 $
	</i></font>
	</p>


	</td>
	<td width="50">

	</td>
	</tr></table>

	<table width="640" border="0" cellpadding="0"
	cellspacing="0">
	<tr><td align="center">

	<hr>




	<a href="index.html">Introduction</a>

	\|

	<a href="news.html">News</a>

	\|

	<a href="documentation.html">Documentation</a>

	\|

	<a href="mailinglist.html">Mailing list</a>

	\|

	<a href="changelog.html">Changelog</a>

	\|

	<a href="download.html">Download</a>

	\|

	<a href="links.html">Links</a>



	<hr>

	</td></tr><tr>
	<td>
	<div align="right">
	<a href="http://www.sics.se/~adam/">Adam Dunkels</a></div>
	</td>
	</tr>
	</table>

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