This paper introduces the design features of a stage lighting network node controller: multi serial port design, automatic discrimination design for data transmission blocking and network interface design. With the development of stage art effect presentation technology, the application of all kinds of intelligent lamps and lanterns is becoming more and more mature, and the number of them is becoming larger and larger. The previous lighting control system can no longer meet the needs of use. Lighting network control system has been used in many new large and medium-sized theatres because of its super data transmission ability, error correction ability and equipment loading and expansion ability (system schematic diagram is shown in Figure 1). Network control nodes are designed in the key parts of stage lighting control room, thyristor room, falsework, overpass and grid top, and powerful network switches and various network devices are equipped. However, in order to make these theatre lighting devices fully integrated into the whole network system, the same key equipment is indispensable, that is, the lighting network node controller. The author develops this stage lighting network node controller, which maps Ethernet data into ordinary DMX light protocol through special lighting network protocol (Art-Net and ACN), transfers network lighting data into multiple serial ports and transmits them to various devices, so that ordinary lighting devices of terminal can also be added to the whole network control system. The realization method is realized by common software to hardware programmable mode. This method can satisfy that each serial port can send a DMX512 signal with a receiving frequency of 250 kb/s in two directions at any time. Finally, eight independent DMX512 channels are realized. Because of the large number of lighting data on the network and high real-time requirements, in order to prevent network congestion, we studied the timely response to serial port signal changes on FPGA, and automatically reduced the transmission interval of network data and saved network resources when the lighting data did not change. A more suitable network interface chip is selected to realize the adaptive functions of 10M/100M Ethernet network and port AutoMDI/MDIX. Multiple serial ports are implemented by FPGA. The resource of the FPGA is abundant. The buffer memory can be built inside the FPGA, which simplifies the circuit and is easy to maintain. The application of FPGA is to design the whole system into each module. Eight dual-port RAM modules correspond to eight serial ports. Each serial module can send or receive serial ports according to the value of the set state register. When a serial port is set to send mode, the serial module is decided by the timer part of the FPGA to send a frame every 30 ms. There is a reason why we choose a signal frame whose period is 30 ms. A DMX512 signal frame is composed of a low level with a head of 88 mu s, plus zero data and 512 light data.
Each data is composed of 11 bits, including one start bit, eight data bits and the last two end bits. If the transmission rate of 250 kb/s is maintained, the transmission time of a data is calculated to be 44 ugs, then a frame of data can normally be sent out in about 23 Ms. Considering that there is still some time between frames and data frames, the 30 ms serial module can send a frame completely in line with the design requirements. MCU (Microcontroller Unit, Microcontroller Unit, also known as MCU) only needs to update the lamp data to write the data into the corresponding dual-port RAM (Random Access Memory, Random Memory) of each serial port. The serial module reads the data regularly and sends it out in a fixed frame format. Therefore, this mechanism makes MCU do not need to spend a lot of valuable system time on data handling, making the system run more efficiently and accurately, thus improving the reliability and safety of products. Several main application modules are designed in the FPGA: dual-port RAM module (see Figure 2), serial sending module and serial receiving module. Because the network node controller can support 4 to 8 serial ports, the status of receiving or sending each serial port is determined by the value in the register of the serial module. This leads to a problem, when all serial ports are set to receive state, it will make these serial ports almost simultaneously write data to dual-port RAM. In order to keep the real-time requirement of lighting data, the first task of MCU at this time is to extract data from dual-port RAM as soon as possible, pack it into network data packets, and send it out through Ethernet. And the interval between frames received by each serial port may be about 25 ms to 30 ms. At this time, the data flow will become very large. After all, thermostatic element the overall data processing capacity of MCU is limited. At this time, the system will become very busy.
This situation is very dangerous to the stability of the whole system. Generally speaking, there is no way to reduce or limit the DMX512 data sent by the console. So is it possible to avoid the excessive fatigue of MCU system? I want to find a way from the actual work of the product.
From the experience of general stage lighting control, the data of every street lighting in a party or a performance is not always changing. Although the DMX512 signal data is continuously sent out frame by frame, most of the time, its signal data value is the same. If FPGA can judge whether the two frames are the same, the problem will be solved. The idea of this method is that if the data values of the two frames are the same, the MCU can ignore and not send new data packets to the network; if they are different, the MCU can update the data packets. In this way, network data traffic will be greatly reduced, and the system processing time spent by MCU to move data will also be greatly reduced. How to compare? Because the control of switching operation of dual-port RAM is handed over to MCU at this time, the FPGA itself can not directly control which part of the content is currently extracted. However, the author finds that the dual-port RAM module can be designed by a reasonable method to solve the problem. Because each received byte data in the serial port is placed in a specific variable, and according to the characteristics of the designed dual-port RAM, the data of the same path in the previous frame will appear in the UART_RAM1_b variable (see figure 3). By comparing the data of this variable with the data in the current dual-port RAM unit, we can judge whether the two frames of light data are the same or not. 。 The network node controller uses a combination of W3150A and RTL8201 (see Figure 4). W3150A is a hardware protocol stack chip, which conforms to the high-speed digital network connection scheme, and embedded TCP/IP protocol stack into the hardware. Its basic function is to process parallel 8/16 bits of data or high-speed serial data, transfer data to Ethernet control chip by TCP/IP or UDP/IP protocol, so as to realize data transmission over Ethernet network. RTL8201 is a chip specially used for Ethernet docking. It is a single port physical layer transceiver. It realizes all the functions of 10 M/100 M Ethernet physical layer. It provides full/half duplex operation and supports the output of twisted pair and optical fiber. We use ArtView software on ARTNET website to test the implementation of Network Connection and Light Network Protocol (Art-Net), which is provided free of charge. The PC is connected with the Ethernet adapter by a cross 8-core common five-type network line, and the IP address of the PC network card is set to 2.0.0.1. This software interface will show that the network adapter has been connected (see figure 6). In the toolbar in the lower left corner, there will be light network node devices connected to the network, and the IP address starts at 2. Step 1: Receive DMX512 data, convert it into light network data and send it to Ethernet for testing. DMX512 signal is sent to any RS-485 serial port of the adapter by a light console. The serial port connected to the console is set to receive state and converted into network data of Universe1.
The adapter is connected to the PC through the wire. If the adapter works properly, each value of 512 signals can be seen in this test software of PC. When the brightness signal of 512 channel lights emitted by the console is 32%, the software data interface is as follows (see figure 7). In the lower left corner of the interface, you can see that the 512-way data is placed in the group Universe1 of the light network data package. The values of each way are received and displayed 32%. The received data is completely correct. The second step: The PC sends the light network data packet to the node controller and converts it into DMX512 signal for testing. Or use a dedicated test software (see Figure 8), go to the send menu and select Art-Net group Universe1. Next, the verification experiment of DMX512 signal is carried out. If any serial port of the node controller is set as the sending state and the received light network data packet is Universe1, the serial port will automatically send DMX512 data. The data format of the serial port can be viewed by the special-purpose oscilloscope (see figure 9). The reset signal of DMX512 can be seen from Figure 9. According to the cultural industry standard WH/T-2008 “DMX512-A Lighting Control Data Transfer Protocol”, the minimum reset signal required is 92 ugs. This product is 92 ugs, which meets the standard requirements. From the display of the oscilloscope (see Figure 10), you can see one of the brightness data units, which has a width of 44 Mu s. Because the rate of DMX512 is 250 kb/s, a unit consists of 11 bits including start and stop bits, each of which is 4 mu s, which fully meets the DMX512 data standard. Through the above test steps, we can confirm that the signal stability of the adapter meets the design requirements. The network node controller of stage lighting mentioned in this paper is especially suitable for performance venues with large number of intelligent lamps and high requirement for lighting artistic effect, and its reliability and safety conform to relevant specifications. It has been popularized and applied in large and medium-sized venues in China. The author will continue to pay attention to its application performance, continue to upgrade and improve, so that this product plays a greater role in various performances.