uIP嵌入式TCP/IP协议栈详解

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"uIP实现的说明手册" uIP是一个轻量级的TCP/IP协议栈，专为嵌入式系统和资源有限的小型设备设计。它的目标是在内存和计算能力有限的硬件上实现基本的网络通信功能。这份文档详细介绍了uIP的实现细节和使用方法。 1. uIP TCP/IP堆栈 - **介绍**: uIP由Adam Dunkels开发，旨在提供一个简单、高效的网络协议栈解决方案，适用于微控制器和其他资源受限的环境。 - **TCP/IP通信**: uIP支持TCP、UDP、ICMP和IP协议，允许设备进行基本的互联网通信，如HTTP、FTP和SMTP等应用。 - **主控制循环**: uIP的核心是一个主控制循环，它处理输入和输出数据包，执行协议栈的各个层的操作。 - **架构特定函数**: uIP设计为可移植的，包含针对不同硬件架构的特定函数，以适应不同的处理器和嵌入式平台。 - **内存管理**: 由于内存限制，uIP的内存管理策略非常重要，它使用紧凑的内存结构和高效的数据包处理。 - **应用编程接口(API)**: uIP提供了一组简洁的API，使得开发者可以轻松地创建和管理网络应用程序。 - **示例**: 文档中包含多个示例代码，帮助开发者理解如何使用uIP进行实际编程。 - **协议实现**: 文档详细列出了uIP中实现的各种网络协议，以及它们的工作方式。 - **性能**: 尽管uIP小巧，但其性能经过优化，能在有限的资源下保持良好的网络通信效率。 2. uIP 1.0模块索引 - 这部分提供了uIP 1.0的所有模块列表，包括protothreads、应用程序、配置函数、初始化函数、设备驱动函数、应用函数、转换函数、设备驱动变量，以及TCP/IP堆栈和架构特定函数等。 3. uIP 1.0层级索引 - 展示了uIP 1.0的类层次结构，有助于理解各组件之间的关系。 4. uIP 1.0数据结构索引 - 列出uIP 1.0中使用的所有数据结构，这些结构用于存储网络包、连接状态和其他网络相关数据。 5. uIP 1.0文件索引 - 提供uIP 1.0源代码文件的完整列表，方便开发者查找和理解代码。 6. uIP 1.0模块文档 - 对每个模块进行了深入的解释，包括protothreads（一种轻量级线程实现）的应用程序、配置和初始化函数、设备驱动和应用函数、转换函数，以及与设备驱动相关的变量。通过这份手册，开发者可以学习如何在嵌入式系统中集成和使用uIP，实现网络通信功能。无论是初学者还是经验丰富的工程师，都能从中受益，更好地理解和利用uIP的强大功能。

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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