uIP 1.0移植指南：嵌入式TCP/IP栈详解

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"这篇文档是关于uIP 1.0版本的嵌入式TCP/IP协议栈的详细说明，由Adam Dunkels编写，日期为2006年6月。uIP是一个轻量级的TCP/IP协议栈，适用于资源有限的嵌入式系统。文档涵盖了uIP的设计原理、主要功能、控制循环、架构特定函数、内存管理、API接口、协议实现、性能评估以及各个模块的详细文档。" 以下是关于uIP 1.0的知识点详解： 1. **uIP TCP/IP协议栈**： - uIP是一个专门为资源受限的嵌入式设备设计的TCP/IP协议栈，它实现了基本的网络通信功能，包括TCP、UDP、ICMP和IPv4。 2. **介绍**： - uIP的目标是为微控制器和嵌入式系统提供一个简单、小巧但功能完备的TCP/IP协议栈，使其能够接入互联网。 3. **TCP/IP通信**： - uIP支持网络层的IP协议，传输层的TCP和UDP协议，以及网络控制协议ICMP，使得设备可以进行数据包的发送和接收。 4. **主控制循环(Main Control Loop)**： - 主控制循环是uIP的核心部分，负责处理网络事件，调用uIP函数来更新协议栈的状态并处理网络数据包。 5. **架构特定函数(Architecture-Specific Functions)**： - 每个硬件平台可能需要特定的设备驱动和底层函数，比如uip_arch.c文件提供了与特定CPU架构相关的功能。 6. **内存管理**： - uIP使用了一种称为“protothreads”的轻量级线程机制，以节省内存，并通过uipopt.h文件进行配置。 7. **应用编程接口(API)**： - uIP提供了一系列API函数，供应用程序使用，用于建立连接、发送和接收数据等。 8. **设备驱动(Device Drivers)**： - 开发者需要为自己的硬件编写设备驱动，例如参考unix/tapdev.c和uip/slipdev.c来实现设备驱动的示例。 9. **主控制循环实现**： - 可以参考unix/main.c中的实现，了解如何在主循环中使用ARP协议，并调用uIP函数。 10. **Makefile和编译**： - 编写Makefile以构建项目，确保包含uIP的源文件，如uip.c，如果使用HTTP服务器，还需要httpd.c、cgi.c和fs.c。如果需要ARP支持，还需要uip_arp.c。 11. **错误调试**： - 平台移植过程中，调试是关键步骤，需要找到并修复所有程序错误。 12. **协议实现**： - 文档详细介绍了uIP中实现的各种网络协议，如TCP、UDP、ICMP和ARP，以及它们的工作方式。 13. **性能**： - 文档还讨论了uIP的性能，这对于资源有限的设备来说是至关重要的。 14. **模块索引**、**层级索引**和**数据结构索引**： - 这些部分提供了uIP 1.0的模块、类层次和数据结构的详细索引，方便开发者查找和理解。 15. **文件索引**和**模块文档**： - 包含了uIP 1.0的文件列表和各模块的文档，有助于开发者理解和使用uIP的各个部分。 uIP 1.0是一个适用于嵌入式系统的TCP/IP协议栈，它的设计目的是在有限的资源条件下提供网络连接能力。通过遵循文档中的步骤，开发者可以将其移植到各种不同的硬件平台上，并利用其提供的API构建网络应用。

10 The uIP TCP/IP stack

1.7.4 Utilizing TCP Flow Control

This example shows a simple application that connects to a host, sends an HTTP request for a ﬁle and

downloads it to a slow device such a disk drive. This shows how to use the ﬂow control functions of uIP.

void example4_init(void) {

uip_ipaddr_t ipaddr;

uip_ipaddr(ipaddr, 192,168,0,1);

uip_connect(ipaddr, HTONS(80));

}

void example4_app(void) {

if(uip_connected() || uip_rexmit()) {

uip_send("GET /file HTTP/1.0\r\nServer:192.186.0.1\r\n\r\n",

48);

return;

}

if(uip_newdata()) {

device_enqueue(uip_appdata, uip_datalen());

if(device_queue_full()) {

uip_stop();

}

if(uip_poll() && uip_stopped()) {

if(!device_queue_full()) {

uip_restart();

}

When the connection has been established, an HTTP request is sent to the server. Since this is the only

data that is sent, the application knows that if it needs to retransmit any data, it is that request that should

be retransmitted. It is therefore possible to combine these two events as is done in the example.

When the application receives new data from the remote host, it sends this data to the device by using

the function device_enqueue(). It is important to note that this example assumes that this function copies

the data into its own buffers. The data in the uip_appdata buffer will be overwritten by the next incoming

packet.

If the device’s queue is full, the application stops the data from the remote host by calling the uIP function

uip_stop(). The application can then be sure that it will not receive any new data until uip_restart() is called.

The application polling event is used to check if the device’s queue is no longer full and if so, the data ﬂow

is restarted with uip_restart().

1.7.5 A Simple Web Server

This example shows a very simple ﬁle server application that listens to two ports and uses the port number

to determine which ﬁle to send. If the ﬁles are properly formatted, this simple application can be used as a

web server with static pages. The implementation follows.

struct example5_state {

char

dataptr;

unsigned int dataleft;

};

void example5_init(void) {

uip_listen(HTONS(80));

uip_listen(HTONS(81));

Generated on Mon Jun 12 11:56:02 2006 for uIP 1.0 by Doxygen

1.7 Examples 11

}

void example5_app(void) {

struct example5_state

s = (struct example5_state)uip_conn->appstate;

if(uip_connected()) {

switch(uip_conn->lport) {

case HTONS(80):

s->dataptr = data_port_80;

s->dataleft = datalen_port_80;

break;

case HTONS(81):

s->dataptr = data_port_81;

s->dataleft = datalen_port_81;

break;

}

uip_send(s->dataptr, s->dataleft);

return;

}

if(uip_acked()) {

if(s->dataleft < uip_mss()) {

uip_close();

return;

}

s->dataptr += uip_conn->len;

s->dataleft -= uip_conn->len;

uip_send(s->dataptr, s->dataleft);

}

The application state consists of a pointer to the data that should be sent and the size of the data that is left

to send. When a remote host connects to the application, the local port number is used to determine which

ﬁle to send. The ﬁrst chunk of data is sent using

uip_send(). uIP makes sure that no more than MSS bytes

of data is actually sent, even though s->dataleft may be larger than the MSS.

The application is driven by incoming acknowledgments. When data has been acknowledged, new data

can be sent. If there is no more data to send, the connection is closed using uip_close().

1.7.6 Structured Application Program Design

When writing larger programs using uIP it is useful to be able to utilize the uIP API in a structured way.

The following example provides a structured design that has showed itself to be useful for writing larger

protocol implementations than the previous examples showed here. The program is divided into an uIP

event handler function that calls seven application handler functions that process new data, act on acknowl-

edged data, send new data, deal with connection establishment or closure events and handle errors. The

functions are called newdata(), acked(), senddata(), connected(), closed(), aborted(), and timedout(), and

needs to be written speciﬁcally for the protocol that is being implemented.

The uIP event handler function is shown below.

void example6_app(void) {

if(uip_aborted()) {

aborted();

}

if(uip_timedout()) {

timedout();

}

if(uip_closed()) {

closed();

}

Generated on Mon Jun 12 11:56:02 2006 for uIP 1.0 by Doxygen

1.7 Examples 13

s->textlen -= uip_conn->len;

s->textptr += uip_conn->len;

if(s->textlen == 0) {

switch(s->state) {

case STATE_HELLO:

s->state = STATE_WORLD;

s->textptr = "world!\n";

s->textlen = 7;

break;

case STATE_WORLD:

uip_close();

break;

}

static void senddata(void) {

struct example6_state

s = (struct example6_state

)uip_conn->appstate;

if(s->textlen > 0) {

uip_send(s->textptr, s->textlen);

}

The application state consists of a "state" variable, a "textptr" pointer to a text message and the "textlen"

length of the text message. The "state" variable can be either "STATE_WAITING", meaning that the

application is waiting for data to arrive from the network, "STATE_HELLO", in which the application is

sending the "Hello" part of the message, or "STATE_WORLD", in which the application is sending the

"world!" message.

The application does not handle errors or connection closing events, and therefore the aborted(), timedout()

and closed() functions are implemented as empty functions.

The connected() function will be called when a connection has been established, and in this case sets the

"state" variable to be "STATE_WAITING" and the "textlen" variable to be zero, indicating that there is no

message to be sent out.

When new data arrives from the network, the newdata() function will be called by the event handler func-

tion. The newdata() function will check if the connection is in the "STATE_WAITING" state, and if so

switches to the "STATE_HELLO" state and registers a 6 byte long "Hello " message with the connection.

This message will later be sent out by the senddata() function.

The acked() function is called whenever data that previously was sent has been acknowleged by the receiv-

ing host. This acked() function ﬁrst reduces the amount of data that is left to send, by subtracting the length

of the previously sent data (obtained from "uip_conn → len") from the "textlen" variable, and also adjusts

the "textptr" pointer accordingly. It then checks if the "textlen" variable now is zero, which indicates that all

data now has been successfully received, and if so changes application state. If the application was in the

"STATE_HELLO" state, it switches state to "STATE_WORLD" and sets up a 7 byte "world!\n" message

to be sent. If the application was in the "STATE_WORLD" state, it closes the connection.

Finally, the senddata() function takes care of actually sending the data that is to be sent. It is called by

the event handler function when new data has been received, when data has been acknowledged, when

a new connection has been established, when the connection is polled because of inactivity, or when a

retransmission should be made. The purpose of the senddata() function is to optionally format the data that

is to be sent, and to call the

uip_send() function to actually send out the data. In this particular example,

the function simply calls

uip_send() with the appropriate arguments if data is to be sent, after checking if

data should be sent out or not as indicated by the "textlen" variable.

It is important to note that the senddata() function never should affect the application state; this should only

be done in the acked() and newdata() functions.

Generated on Mon Jun 12 11:56:02 2006 for uIP 1.0 by Doxygen

14 The uIP TCP/IP stack

1.8 Protocol Implementations

The protocols in the TCP/IP protocol suite are designed in a layered fashion where each protocol performs

a speciﬁc function and the interactions between the protocol layers are strictly deﬁned. While the layered

approach is a good way to design protocols, it is not always the best way to implement them. In uIP, the

protocol implementations are tightly coupled in order to save code space.

This section gives detailed information on the speciﬁc protocol implementations in uIP.

1.8.1 IP — Internet Protocol

When incoming packets are processed by uIP, the IP layer is the ﬁrst protocol that examines the packet.

The IP layer does a few simple checks such as if the destination IP address of the incoming packet matches

any of the local IP address and veriﬁes the IP header checksum. Since there are no IP options that are

strictly required and because they are very uncommon, any IP options in received packets are dropped.

1.8.1.1 IP Fragment Reassembly

IP fragment reassembly is implemented using a separate buffer that holds the packet to be reassembled. An

incoming fragment is copied into the right place in the buffer and a bit map is used to keep track of which

fragments have been received. Because the ﬁrst byte of an IP fragment is aligned on an 8-byte boundary,

the bit map requires a small amount of memory. When all fragments have been reassembled, the resulting

IP packet is passed to the transport layer. If all fragments have not been received within a speciﬁed time

frame, the packet is dropped.

The current implementation only has a single buffer for holding packets to be reassembled, and therefore

does not support simultaneous reassembly of more than one packet. Since fragmented packets are uncom-

mon, this ought to be a reasonable decision. Extending the implementation to support multiple buffers

would be straightforward, however.

1.8.1.2 Broadcasts and Multicasts

IP has the ability to broadcast and multicast packets on the local network. Such packets are addressed

to special broadcast and multicast addresses. Broadcast is used heavily in many UDP based protocols

such as the Microsoft Windows ﬁle-sharing SMB protocol. Multicast is primarily used in protocols used

for multimedia distribution such as RTP. TCP is a point-to-point protocol and does not use broadcast or

multicast packets. uIP current supports broadcast packets as well as sending multicast packets. Joining

multicast groups (IGMP) and receiving non-local multicast packets is not currently supported.

1.8.2 ICMP — Internet Control Message Protocol

The ICMP protocol is used for reporting soft error conditions and for querying host parameters. Its main

use is, however, the echo mechanism which is used by the "ping" program.

The ICMP implementation in uIP is very simple as itis restricted to only implement ICMP echo messages.

Replies to echo messages are constructed by simply swapping the source and destination IP addresses of

incoming echo requests and rewriting the ICMP header with the Echo-Reply message type. The ICMP

checksum is adjusted using standard techniques (see RFC1624).

Since only the ICMP echo message is implemented, there is no support for Path MTU discovery or ICMP

redirect messages. Neither of these is strictly required for interoperability; they are performance enhance-

ment mechanisms.

Generated on Mon Jun 12 11:56:02 2006 for uIP 1.0 by Doxygen

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