With the large-scale application of industrial Ethernet, the embedded industrial Ethernet system has also increasingly penetrated into the field of industrial control. The embedded industrial Ethernet system with ColdFire microprocessor and ARM processor as the hardware platform has been obtained. widely used. However, because the development platforms of these systems are not entirely aimed at the application of industrial Ethernet, the problem of waste of hardware resources or insufficient resources often occurs in practical applications. Development systems often require external PLD chips to perform logic control of peripheral devices , There is a bottleneck of the interface rate. The NIOS processor based on SOPC technology can solve this problem. Clinux. ï Considering the cost performance and on-site control needs, the operating system of the controller is adopted
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hardware design
The hardware design of the controller is completed in SOPC Builder and QuartusII. They can be used to flexibly customize the various features and even instructions of the NIOS CPU. You can use the large amount of IP provided by Altera to accelerate the development of NIOS peripherals and improve the performance of the peripherals. You can also use third-party IP, or VHDL, Verilog to customize the peripheral .
The hardware of the embedded industrial Ethernet controller is divided into three parts: FPGA part, memory part and peripheral component part, as shown in Figure 1. The FPGA selected in this article is CYCLONE EP1C6.
What needs to be designed in the SOPC Builder is the FPGA part. The component modules included in the NIOS system to be built are: a NIOS CPU core, an Avalon bus controller used to connect the NIOS core, and an internal memory Boot ROM to store startup and debug programs A UART serial communication circuit module (RS232 core), an internal timer and some general I / O peripheral interface modules. In order to make the NIOS system work properly, an RS232 communication port, RJ45, several LEDs and digital tubes, 16M SRAM and 4M Flash ROM must be connected to the periphery of the FPGA.
software design
Since the system composed of the NIOS CPU and its peripherals in hardware development is self-customized, the mapping of memory and peripheral addresses are different, so a proprietary SDK (software development kit) is required. After completing the hardware development of NIOS, SOPC Builder can automatically generate SDK.
The development of the software part is almost the same as the development of the usual embedded system. The only difference is that the embedded system here is customized and tailored by itself, which is less limited by the hardware.
The entire embedded industrial Ethernet controller has the following characteristics:
1) High flexibility. Because the microprocessor adopts NIOS, the system resources can be flexibly allocated, and overcome the shortcomings of using interface rate bottlenecks in other processors, and adapt to the requirements of industrial Ethernet real-time data.
2) Clinux is very small after reduction, and has Ethernet function, so that it can easily achieve miniaturization and networking of the controller; ï very high integration. Because NIOS has rich interface resources, and
3) High real-time performance. The controller fully considers the real-time nature of the system when designing the hardware and software. The hardware design uses high-speed A / D (500kHz) and multiple D / A outputs, which enables key signals to be sampled and output in time to ensure "hard real-time"; the RTlinux module is added to the operating system to ensure "soft real-time" .
Practical application
To meet the needs of an enterprise's production site, the controller is applied to an Ethernet-based control system. Aiming at the strict requirements of network reliability parameters on site, the use of ring network topology can increase the reliability of the network.
When solving the real-time problem of the network, the concept of control domain (Control Domain) is adopted, which will control the on-site zoning and reduce the resource competition in each control zone. The control area communicates through switched Ethernet switches. Each control area contains Ethernet switches and embedded industrial Ethernet controllers, as well as some transmitters and actuators, as shown in Figure 2. The system has the following characteristics:
1) Flexibility. SOPC technology makes the design and debugging of system hardware and software very convenient.
2) Reliability. The network topology of the control system uses a ring architecture, which greatly enhances the reliability of the backbone network. At the control network layer, by dividing the control area, the control risk is dispersed; and the embedded industrial Ethernet controller is used inside the control area to centrally control the entire control area and reduce the control cost. Practice has proved that this decentralized and centralized control structure is very effective.
3) Real-time. By dividing the control area, each control area is connected to the backbone network through the switch, and the transmission and execution structure information in each control area does not occupy the backbone network resources. In this way, the network load in each control area can be reduced to a very low level (<5%), which improves the real-time performance of the network. The hardware and software design of the embedded industrial Ethernet controller consider the real-time requirements, and further improve the real-time performance of the system under the network layer.
Conclusion
In this paper, the embedded industrial Ethernet controller is developed and researched, and SOPC technology is proposed to solve the problem of interface speed bottleneck in the hardware design of the controller, and the real-time performance of the controller is improved. The experimental results show that the system is stable and reliable.