With examples, the network node controller of theatre stage special lighting is discussed in some large theatres for reference. Stage-specific lighting network node controller successfully transforms the network lighting data into multiple serial port data by using the special lighting network protocol (sACN and Artnet) through data mapping of ethernet, and then synchronously distributes the network lighting data to many devices. Finally, the common lighting equipment at the end can become the whole network control system. In the later stage of engineering practice and experiment, we should continue to improve it, and focus on the following three aspects for further research, so as to improve the performance of node controller. Because of the high real-time requirement of bright point data and the high frequency of occurrence on the network, we should study the responsiveness of serial signal changes on the FPGA, so as to avoid the occurrence of network congestion. At the same time, when the brightness data does not change, it is necessary to shorten the transmission interval between network data automatically, which is conducive to saving network resources. The implementation of multi-serial port based on FPGA is given. The hardware programmable mode is realized by software, so that all serial ports can send the DMX512 signal with the receiving frequency of 250kb/s in real time and bidirectionally. Finally, eight independent DMX512 channels are realized.
The best network interface chip is determined to realize the self-adaptive function of port AutoMDI/MDIX and 10M/100M Ethernet network. Multiple serial ports are implemented by FPGA. Because of the abundant resources of the FPGA, the function of buffer memory can be realized in the FPGA, which not only provides convenience for maintenance, but also simplifies the circuit. The application of FPGA means that the whole system is designed as many modules, and the eight double port RAM modules correspond to eight serial ports. Each serial module can receive or send serial ports by setting the value of the state register. After setting a serial port to send mode, the serial module sends one frame per 30ms from the timer of the FPGA. The reason for choosing a signal frame with a period of 30 ms is that DMX512 signal frame is composed of zero data, a low level with a head of 88us and 512 brightness data. Each data is up to 11 bits, including 8 bits, one start bit, one end bit and one state bit.
If we want to continue sending data at 250 KBS and the time of transmitting data is 44 us, we should ensure that the time of sending a frame of data is about 23 Ms. In addition, the reserved time between frames should be considered to ensure that the 30ms serial module sends a frame to the standard completely. However, the MCU only needs to write in the dual-port RAM corresponding to each serial port in the process of updating the data, so that the serial module reads the data regularly and transmits it according to the fixed frame format.
Therefore, this kind of mechanism makes MCU not need to spend a lot of valuable system time on data handling, so that the operation of the system becomes more accurate and efficient, thereby improving the safety and reliability of products. In the field of FPGA, several main application modules are designed, including serial sending module, dual-port RAM module and serial receiving module. Since the network node controller supports up to 4 to 8 serial ports, thermostatic element the value in the register of the serial module determines the status of each serial port, whether it is sent or received. However, once all the serial ports are in the receiving state, it is almost synchronous for such serial ports to write data to dual-port RAM.
In order to ensure real-time lighting data, MCU must extract data from dual-port RAM as far as possible, pack it into network data packets, and then transmit it through Ethernet. However, the time interval between frames received by each serial port may be only 25 ms to 30 ms, at which time the data flow will rapidly increase. Because of the limitation of MCU’s overall data processing ability, the system will become very busy at this time, which is not conducive to the stability of the whole system. Generally speaking, we can’t limit or reduce the DMX512 data transmitted by the console.
Perhaps the data received is frame by frame. Some people will think that this will affect the MCU system? The following will be the actual working conditions of the product as a starting point to find solutions. Based on the experience of lighting control in general, we know that the lighting data of every performance or evening is not always changing in real time. Although DMX512 signal data is sent frame after frame, its brightness signal values are consistent in most of the time. It can be seen from this that if the FPGA can successfully judge whether the two frames are consistent or not, the problem can be solved accordingly. That is to say, if the data values of the two frames are identical, the MCU can not send new data packets to the network; otherwise, the data packets should be updated again.
In this way, the network data flow can be greatly reduced and the system processing time can be saved. How to compare, because MCU has the switching control of dual-port RAM at this time, and the FPGA does not support the direct extraction and control of a piece of content. However, through a series of analysis, we can adopt reasonable means to design dual-port RAM module function, which has handled this kind of problem. Because each received byte data in the serial port is placed in a specific variable.
However, from the characteristics of dual-port RAM, the data of the same path in the previous frame will appear in the designed UART_RAM1_b variable after entering dual-port RAM. By comparing the data in the dual-port RAM unit with the variable data, we can judge whether the two frames of light data are consistent or not. The free ArtView software on ARTNET website can be used for testing after the light network protocol is connected to the network. An eight-core common network line is used to connect the Ethernet adapter with the PC. The IP address of the network card of the PC is set to 2.0.0.1. This software interface can show that it has been connected with the network adapter. At the same time, it will appear in the toolbar in the lower left corner. The IP address is at the beginning of 2.
The location of the network node with lights is connected to the network. The first step is to receive DMX512 and gradually convert it into a light network packet, which is then transmitted to the test of ethernet. DMX512 signal is sent out by a light console and received by the 485 serial port of the adapter. At the same time, the serial port connected to the console is set to receive state and transformed into the network data of Universe1.
In fact, the adapter is connected by a PC and a wire. If the adapter is in normal working condition, all values of the 512 signals can be seen on the test software of PC. Once the brightness signal of 512 lights issued by the console is 32%, Figure 2 shows the software data interface. From the bottom left corner of the interface, we can see that this 512-way data is placed in the group Universe1 of the light network data package.
The values of each way can be received, and the data are all paired, showing 32%. The second step is to convert the light-emitting network data package of PC into DMX512 signal test in the node controller. A professional test software is applied to select Artnet group Universe1 in the sending menu interface. Then the verification experiment of DMX512 signal is carried out. A serial port of any selected node controller is set to send state. If the received light network data package is Universe1, the serial port will automatically send the DMX512 data. The data format of the serial port can be seen through the special-purpose oscilloscope. Figure 3 shows the actual display of the oscilloscope, from which we can find the header data of DMX512. The manual stipulates that the data head low level must exceed 88us, while the product we designed is 92us. The actual display of the oscilloscope is shown in Figure 4. From the figure, we can easily see a luminance data unit with a width of 44 us. Since the rate of DMX512 is 250 Kbs, each unit is composed of stop bit and start bit. The total number of them is 11 bits, and each bit is 4 us, which is completely consistent with the DMX512 data standard. Relying on the above test process, we can see that the signal of this adapter is stable and up to standard. The theater stage lighting network node controller has been used for some time in some large theaters. Because of its perforated design, it is most suitable for performing intelligent lamps with large number of computer lights and high lighting performance. For this reason, we will continue to pay attention to and upgrade the performance in the actual application process, so that the practicality, safety, reliability and maintainability of the product are consistent with the actual application, so as to play a better role in the performance of the stage theater.