Light Weight TCP / IP protocol stack and application migration OpenTCP -TCP/IP, Ethernet, remote communications – Communications Industry
Introduction As industrial control and computer technology, data transmission on a higher demand, the rapid development of a variety of bus technologies. Among them, the use of Ethernet technology for data remote Communicate And connected to the Internet, has become an important field of industrial and domestic development, the future almost all the industry equipment and home appliances with Internet connectivity are required. At present, composed of MCU and other embedded systems have been widely used in industry, household appliances and other fields, the application of embedded system requirements on the network more and more, so in Embedded System TCP / IP protocol, has become embedded systems research focus.
Traditional TCP / IP protocol in embedded systems with limited resources to achieve them is difficult, substantial resources must be spent to ensure the reliability of data transmission and data flow control, thus higher real-time requirements embedded in the field, unable to meet real-time requirements. Therefore, the study and to improve the embedded TCP / IP protocol stack to meet the performance requirements of embedded systems has important practical significance.
1 hardware platform and OpenTCP Introduction
1.1 hardware platform The hardware of the system performance by the ADE7758 energy metering chip, ARM processor, 2MBNORFlash, 64MBSDRAM and Ethernet interfaces and other components. ADE7758 internal integrated 6-channel 16-bit – ADC, high-performance DSP, voltage reference and temperature sensor circuit, the 1000:1 dynamic range error is less than 0.1%; to provide active, reactive and apparent power, voltages, current RMS and waveform sampling and other data; three-phase three-wire / three-phase four-wire compatible; DSP internal reactive power was compensated; provide independent active energy and reactive energy pulse output, ideal for three-phase energy measurement. Measured three-phase voltage, current post by the sensors and conditioning circuits, into the ADE7758's A phase, B phase, C phase voltage and current inputs; calculated by the ADE7758, converted to active power, reactive power, apparent power complex power and other energy information and data through the SPI interface output ADE7758. MCU read out data and processing power then deliver the LCD display and network interfaces. Hardware block diagram in Figure 1.
Power for remote monitoring of computer data, software, part of the protocol stack used OpenTCP as complete data communication. OpenTCP British Vi-ola developed for 8 / 16 bit MCU and open source TCP / IP stack. And general embedded TCP / IP protocol stack (such as lwIP, uIP) compared to the more streamlined the code does not require operating system support, can be cut as needed, all with ANSIC prepared to support Ethernet, SLIP, ARP, RARP, ICMP, TCP, UDP; application layer support TFTP, TEL-NET, HTTP, SMTP, POP3, DNS, etc., are provided for the application layer protocol callback interface, user-friendly application design.
1.2 protocol stack features General-purpose computer running TCP / IP protocol stack is too complex, need to take up a lot of system resources, and embedded applications often have very limited resources. Therefore, the need for the traditional TCP / IP protocol stack to be simplified. OpenTCP in the design to improve the efficiency of the protocol stack, while maintaining the high performance, embedded system requirements on the TCP / IP was part of the streamlining and optimization, so that it can achieve a variety of MCU architecture, to reduce resource consumption, to meet the requirements of embedded applications. Specific features are as follows:
As network functionality of embedded systems have different requirements, OpenTCP application requirements can choose the necessary agreements, to reduce code size and data memory of the occupation.
According to the characteristics of embedded systems application environment, generally as a server-side, to communicate with the achievement of a complete TCP / IP devices, communication is more reliable and does not require complex routing, IP fragmentation, re- installed, TCP flow control, congestion control. Therefore, OpenTCP in simplified TCP, IP and other protocols to achieve the abolition of all the IP options and TCP options (including IP-sub); TCP flow control window length 1, that message transmission is based on the stop a waiting mode. Avoid the complex flow control and partition processing, embedded network applications to meet the requirements. TCP state machine also had some simplified.
OpenTCP against TCP / IP agreement, some of the greatest impact on performance?? Buffer management is optimized, using zero-copy technique, that is, network card drivers and protocols have no data copying process to decrease the system resources occupation, simplifying buffer management and improve the real-time.
TCP / IP is layered, each layer has its own data format. Data transmission between the layers need to keep packing and unpacking to handle, and a copy of the data, will greatly increase the system memory and computing power on the overhead, reduce system performance. In OpenTCP protocol stack, each layer are not used for data transmission buffer is passed between the protocol stack data pointer. Receiving data, each layer of this layer of data processing has been completed, data will be processed on the level of the data pointer to the head; to send data, a similar process is achieved.
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