STM32F2x7xx微控制器LwIP TCP/IP栈应用演示

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本应用笔记（AN3384）详细介绍了一个针对STM32F2x7xx系列微控制器的LwIP TCP/IP栈演示项目。STM32F2x7xx系列微控制器以其高质量的10/100Mbit/s以太网接口而闻名，支持MII和RMII标准，以适应不同的物理层（PHY）连接。在利用以太网通信时，TCP/IP栈是实现本地或广域网络通信的关键组件。 LwIP是一种专门为嵌入式设备设计的开源TCP/IP栈，该演示包构建在其上，提供了九个运行实例，覆盖了不同的应用场景和编程接口： 1. **独立运行模式（不依赖RTOS）**： - **Web服务器**：展示了如何使用LwIP在微控制器上构建一个基本的HTTP服务器。 - **TFTP服务器**：用于传输文件的简单文件传输协议服务器。 - **TCP回显客户端**：通过TCP进行数据发送和接收验证。 - **TCP回显服务器**：接收并回应客户端的数据请求。 - **UDP回显客户端**：使用用户数据报协议进行数据交换测试。 - **UDP回显服务器**：接收并响应UDP数据包。 2. **与FreeRTOS操作系统集成**： - **基于netconn API的Web服务器**：FreeRTOS环境下，通过netconn库实现网络连接管理。 - **基于socket API的Web服务器**：使用更高级别的socket接口构建的服务器。 - **TCP/UDP回显客户端和服务器**：在RTOS中演示了并发TCP和UDP通信。这个演示包不仅提供了解决方案，还展示了如何将LwIP与STM32F2x7xx的硬件特性结合起来，以及如何根据不同需求选择合适的编程接口来开发高效的网络应用。通过学习和实践这些示例，开发人员可以熟悉LwIP的工作原理，优化TCP/IP协议栈在嵌入式系统中的性能，并构建具有可靠性和高效性的网络服务。

AN3384 LwIP stack overview

Doc ID 018698 Rev 2 9/47

2.3.2 Netconn API

The netconn API is high-level sequential API which has a model of execution based on the

blocking open-read-write-close paradigm.

To function correctly, this API must run in a multi-threaded operation mode where there is a

separate thread for the lwIP TCP/IP stack and one or multiple threads for the application.

Table 3 provides a summary of the netconn API functions.

2.3.3 Socket API

lwIP offers the standard BSD socket API. This is a sequential API which is internally built on

top of the netconn.

Table 3 provides a summary of the main socket API functions.

Table 3. Netconn API functions

API function Description

netconn_new

Creates a new connection.

netconn_delete

Deletes an existing connection.

netconn_bind

Binds a connection to a local IP address and port.

netconn_connect

Connects to a remote IP address and port.

netconn_send

Sends data to the currently connected remote IP/port (not applicable for

TCP connections).

netconn_recv

Receives data from a netconn.

netconn_listen

Sets a TCP connection into a listening mode.

netconn_accept

Accepts an incoming connection on a listening TCP connection.

netconn_write

Sends data on a connected TCP netconn.

netconn_close

Closes a TCP connection without deleting it.

Table 4. Socket API functions

API function Description

socket

Creates an new socket.

bind

Binds a socket to an IP address and port.

listen

Listens for socket connections.

connect

Connects a socket to a remote host IP address and port.

Accepts a new connection on a socket.

read

Reads data from a socket.

write

Writes data on a socket.

Closes a socket (socket is deleted).

LwIP stack overview AN3384

10/47 Doc ID 018698 Rev 2

2.4 lwIP buffer management

2.4.1 Packet buffer structure

lwIP manages packet buffers using a data structure called pbuf. The pbuf structure enables

both the allocation of dynamic memory to hold packet content and lets packets reside in the

static memory.

Pbufs can be linked together in a chain. This enables packets to span over several pbufs.

Figure 2. Pbuf structure

● next: pointer to next pbuf in a pbuf chain

● payload: pointer to packet data payload

● len: length of the data content of the pbuf

● tot_len: the sum of pbuf len plus all the len fields of the next pbufs in the chain

● ref (on 4 bits) reference count: indicates the number of pointers that reference the pbuf.

A pbuf can be released from memory only when its reference count is zero.

● flags: (on 4 bits) indicate the type of pbuf.

lwIP defines three types of pbufs, depending on the allocation type:

● PBUF_POOL: pbuf allocation is performed from a pool of statically pre-allocated pbufs

that have a predefined size. Depending on the data size that needs to be allocated, one

or multiple chained pbufs are allocated.

● PBUF_RAM: pbuf is dynamically allocated in memory (one contiguous chunk of

memory for the full pbuf)

● PBUF_ROM: there is no allocation for memory space for user payload, the pbuf

payload pointer points to data in the ROM memory (it can be used only for sending

constant data).

For packet reception, the suitable pbuf type is PBUF_POOL, it allows to rapidly allocate

memory for the received packet from the pool of pbufs. Depending on the size of the

received packet, one or multiple chained pbufs are allocated. The PBUF_RAM is not

suitable for packet reception because dynamic allocation takes some delay. It may also lead

to memory fragmentation.

For packet transmission, depending on the data to be transmitted, the user can choose the

most suitable pbuf type.

PAYLOAD

LEN

TOT?LEN

FLAGS

REF

2OOMFORPACKETHEADERS

NEXTPBUFSTRUCTURE

-36

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