Introduction of Mobile Email Terminal Based on S3C2410 Processor

The system is a wireless email terminal based on WLAN (Wireless Loeal Area Network). Users can easily input email content on the touch screen with a stylus, and send and receive emails through a USB wireless network card. When using a keyboard to input, plugging in a USB keyboard can also complete the function of inputting information. In terms of email sending and receiving, standard STMP and POP3 protocols are used. Considering the limited Flash storage capacity of general embedded devices, the system provides a USB disk storage function, and users can transfer emails to a large-capacity USB disk. Compared with traditional email clients, the use of a wireless network card can realize the sending and receiving of emails without connecting to a network cable, which is suitable for remote mountainous areas and places with harsh environments; the use of an embedded terminal is highly mobile, which is convenient for users to perform real-time email operations.

1 System Hardware Design

Based on the convenience and simplicity of development, the system hardware platform adopts HHARM2410 development platform. The hardware of this development platform is powerful, with rich interfaces and convenient development. Its processor adopts S3C2410 processor based on ARM920T core, with the highest frequency up to 203 MHz, and has the characteristics of low power consumption and high integration, with 8 MB Flash, 32 MB SDRAM, touch screen, master-slave USB interface. It has rich built-in resources and high cost performance, which can fully meet the needs of the system.

When sending emails, input devices are essential. Among the input devices such as touch screens, styluses and keyboards, USB keyboards are used in this system design because of their universality. The USB keyboard driver only needs to enable UHCI in the Linux kernel, the human-machine interface related parts, add "USB Human Intelface Device (full HID) sport" to the kernel, and then add a header file (input.h) to the application.

Since the system is a mail system based on wireless LAN, it uses wireless network card prism device, which complies with 802.11b standard. The wireless network card is based on USB and is easy to use.

The development board is connected to the PC via a serial cable and an Ethernet cable to form a cross-compilation development environment. The USB interface on the development board is connected to an external wireless network card, which is then connected to the Internet to send and receive emails. Figure 1 is a hardware block diagram of the wireless system.

2 System Software Design

2.1 Establishing a cross-compilation environment

The application development environment based on embedded system is composed of target system hardware (S3C2410 development board) and host PC. The target hardware development board is used to run the kernel compilation of embedded operating system, and the development and debugging of application programs need to be completed through the host PC. The embedded system is connected to the host through network cable and RS232 serial cable respectively, and the host runs Redhat9.O Linux operating system.

Install the development environment software package under the Redhat Linux operating system of the host. Here, the entire HHARM2410 development environment is installed. The software package can be downloaded from Huaheng's website. After decompression, execute the following command:

#cd/mnt

#./cce //Enter the Chinese environment

#./arminst //Execute the installation program

After the development environment is installed, two subdirectories will be created under the root directory, namely the working directory /HHARM2410-R3 and the cross-compilation environment directory /opt/host/arm41. When compiling, you must use /opt/host/arm41/bin/arm41-unknown-linux-gcc instead of directly using gcc.

2.2 Configuring the wireless network card

After the wireless network card is installed, load the wireless network card driver by loading the kernel module. The specific steps are as follows:

2.3 Mail Protocol

The mail protocol uses the common SMTP/POP3 protocol. POP stands for Post Office Protocol, which is used to receive emails. It uses TCP port 110. Currently, the third version is commonly used, so it is referred to as POP3. POP3 still uses the Client/Server working mode. In the actual process of receiving and retrieving mails, the application layer protocol POP will direct the TCP protocol and use the IP protocol to split a large mail into several data packets for transmission on the Internet. Figure 2 shows the process of receiving mails.

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SMTP is called Simple Mail Transfer Protocol. Its goal is to provide users with efficient and reliable mail transmission. An important feature of SMTP is that it can relay mail during transmission, that is, mail can be transmitted by hosts on different networks in a relay manner. SMTP has two working modes: 1) Email is transmitted from the client to the server; 2) It is transmitted from a certain server to another server. SMTP is a request/response protocol. It listens to port 25 to receive user's mail request and establish an SMTP connection with the remote mail server. Figure 3 shows the process of sending mail.

2.4 User Interface

The user interface design of this system adopts MiniGI under Linux. MiniGUI is a small image user interface support system with powerful functions, beautiful interface and convenient development. It is one of the excellent domestic embedded Linux-based graphical interfaces. Compared with similar graphical user interfaces abroad, it fully supports Chinese, which is conducive to developing applications on Chinese platforms. Min-iGUI provides a complete multi-window mechanism, which is divided into 4 categories: main window, dialog box, control window and sub-window, and realizes the window message transmission mechanism; it has the advantages of lightweight, high performance, high reliability and configurability, and is very suitable for embedded applications.

3 Conclusion

On the embedded Ifinux platform of HHARM2410, a mobile email terminal based on ARM920T is designed in detail, which not only improves the speed and reduces the cost, but also provides great convenience in places without conventional network transmission conditions.

The hardware and software design of the wireless email terminal under the S3C2410+wireless network card system platform adopts an embedded terminal. Compared with the traditional email terminal "microcontroller+wireless network card" system structure, it has strong mobility, can realize rich protocol interfaces, and is easy to transplant, making it more convenient for users to send data in real time. This system design has certain application value and guiding significance in the wireless application of embedded devices.