-
-Using lwIP with or without an operating system
-
-
-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.
-
-
-
-
-The lwIP single-threaded core
-
-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.
-
-
-The core components can be viewed as a software library which has the
-following interface:
-
-
-- ip_input(pbuf, netif): Takes an IP packet and the incoming network
-interface as arguments and does the TCP/IP processing for the packet.
-
- tcp_tmr(): Should be called every 100 ms. Does all TCP
-timer processing such as doing retransmissions.
-
-
-Because none of the core functions ever needs to block when run in a
-single-threaded environment, the sys_arch (the operating
-system abstraction layer) does not need to implement locking
-semaphores or mailboxes. In future versions of lwIP, the dependancy of
-the sys_arch will be removed in the single-threaded case.
-
-
-A simple main loop for a single-threaded system might look
-like this:
-
-
- 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();
- }
- }
-
-
-lwIP in a multi-threaded system
-
-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.
-
-
-
-
-
-The inter-thread communication is implemented in the two files
-api_lib.c and api_msg.c. The former contains the
-functions used by the application programs and the latter implements
-the TCP/IP stack interface. A third file, tcpip.c, handles
-incoming packets and timer events as described in the previous
-section.
-
-
-
-When run in a multi-threaded environment, incoming packets are handled
-by the function tcpip_input(), which takes the same arguments
-as the ip_input() function. The difference between the two
-functions is that the tcpip_input() 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.
-
-
-
-When being run in a multi-threaded system, timer events are taken care
-of internally in tcpip.c.
-
-
-
-
-$Date: 2002/10/19 13:00:03 $
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