With the improvement of computer performance and the increase of communication volume, the traditional local area network has exceeded its own load more and more. Switched Ethernet technology emerged at the historic moment, greatly improving the performance of the local area network. The network switch can significantly increase the bandwidth and establish a relatively dispersed network. Each port of the LAN switch can transmit information in parallel, safely, and in real time, and has stable performance, flexible structure, easy installation, and easy management, which can well meet the broadband access needs of enterprise networks and telecom operators.
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1 Hardware design of network switch
With people's demand for security and high bandwidth in network applications, network switches are becoming more and more widely used. This switch uses the ROX bus of the AL101 chip to connect three 8-port switch chips to form a 24-port switch, which meets the needs of users for multiple switch ports.
1.1 Circuit performance requirements
The high-speed PCB circuit board of the switch has relatively high requirements on EMC and ESD. It uses 75MHz, 50MHz high-speed clocks, the precision of the crystal oscillator is less than 50PPM, and the clock needs to be sent to different chips through the clock distribution circuit, and the phase difference between the distributed clocks is less than 2ns.
The switch has 24 10/100M adaptive ports, and each port can achieve wire-speed switching. According to user needs, the port can be set for 10/100M speed, full/half duplex, flow control, static MAC address, mirroring, VLAN, etc.
1.2 The principle block diagram of the switch
The switching technology of this switch adopts store-and-forward mode, which is mainly composed of five parts: interface unit, switching unit, management unit, light display unit and power interface unit.
After the RJ45 interface receives the data packet of the Ethernet frame structure, it is sent to the PHY (physical interface chip) after transformer isolation and impedance matching. In this chip, the conversion of the analog signal to the digital signal of the RMII interface is completed, and the link status is obtained , Conflict, whether the information is too long, speed and other information.
Data enters the switching chip (consisting of three chips, forming a loop through the ROX bus, which can complete the data exchange between the three chips), the switching chip will obtain the destination address and source address of the data, and perform processing on the Ethernet frame Error checking. The switch chip saves the source address in its own MAC address table, and then matches the destination address with the address in the MAC address table to obtain the corresponding port to which the data will be forwarded. If the destination port is in the same switching chip, the data is taken from the SGRAM and forwarded to the corresponding port; if the destination port is not in the same switching chip, the data is transmitted to the corresponding switching chip through the ROX bus, and then forwarded; If the corresponding destination address is not found in the MAC address table, the frame is forwarded to all ports belonging to the same VLAN except the source port or a certain uplink port (related to the setting of the switch chip register).
The display of the light is given by the PHY. Through the display of the light, you can observe the working speed, connection and data transmission and reception of each port.
During each power-on or reset of the switch chip, it first reads the contents of the external EEPROM to initialize the switch chip registers. The content of the switch chip register can be read and written through the PC's management program or the PC's hyper terminal to control or read the working configuration of the switch.
2 Software design of network switch
The software of the entire network switch system includes the control software of the microcontroller, the EEPROM configuration data and the management program of the PC.
The control software of the one-chip computer mainly completes the reading and writing of the register and the communication with the PC. Through this management unit, the switch can be configured into various working modes to meet the needs of different users.
The exchange chip is connected to the EEPROM (24C02) through the I2C bus for saving configuration data. When the device is turned on or reset, the device will read these data from the EEPROM for system initialization.
The management program of the PC is that the user connects the serial port of the PC to the system equipment, and configures the system easily through the management program interface of the PC.
2.1 Software design controlled by single chip microcomputer
The management unit is composed of a single-chip microcomputer and a serial port, and the register of the EEPROM or exchange chip is configured through the PC. The microcontroller mainly completes the reading and writing of registers and the communication with the PC. The serial port serves as a connection with the PC. There is also a level conversion chip between the microcontroller and the serial port to complete the communication between the microcontroller and the PC. Signal conversion. Through the management unit, the switch can be configured into various working modes to meet the needs of different users, such as: 10/100M speed setting, full/half duplex setting, flow control, static MAC address setting, mirroring setting, broadcast storm control , VLAN settings, etc.
