Embedded Linux-based Communications Systems Research

The development of science and technology has improved people's production efficiency and living level greatly. With the development of society, a lot of scientific and technological invention and products arise at the historic moment, and the most of them are based on embedded system. The embedded system, based on computer technology, which can be modified in both hardware and software, is used to meet the demands of function, reliability, low cost, solidity, and energy cost of an application system. It is widely used in many fields such as electronic, industry, aviation and so on.This text has introduced a kind of embedded mail receiving and sending device utilizing embedded microcontroller S3C44B0X as the CPU, basing on uClinux operating system. The core of the hardware S3C44B0X is a product of Samsung. It is a high-performance microprocessor that is 16/32 bits RISC and has a high proportion of the price. The kernel of microcontroller is ARM7TDMI RISC (the highest mainly frequency is 66MHz). It has offered the abundant built-in part, has integrated various kinds of function in a chip.In order to realize the function of the system, the main peripheral interface includes: SDRAM, is used for storing operating system and procedure; Network chip RTL8019AS, is used for joining the network; The unit of keyboard, is used for entering instruction; Unit LCD, is used for showing the result; Unit of serial port, is used for debugging and development; the interface of JTAG, is used for debugging systematically and development.The embedded operating system adopts uClinux. As a kind of outstanding embedded operating system, it is a highly optimizing, embedded Linux with compact code through changing standard Linux kernel. It keeps most advantages of Linux, has steady performance, good transplantation, outstanding network function, and supports various kinds of mainstream embedded microprocessors that have no memory manage unit.This text utilizes the long-range land tool Telnet in TCP/IP protocol to land the mail server to receive and dispatch the E-mail. In order to realize the function of the system, it needs to finish the transplantation and disposition of the embedded kernel according to the actual conditions.The POP3 protocol is the key of receiving E-mail. The SMTP protocol is the key of sending E-mail.P0P3 refers to Post Office Protocol Version 3, is called the mailbox protocol, which is responsible for receiving the mail. Its port is 110. SMTP refers to Simple Mail Transfer Protocol, is called the simple mail transmit protocol, is responsible for sending the mail. SMTP port is 25.The design realizes that the function of receiving and sending mail, reach the re-set target, it can land the mail server through Telnet and utilize POP3 and SMTP to realize receiving and sending mail.