CN111510359B

CN111510359B - Low-delay end-to-end communication method based on CAN bus

Info

Publication number: CN111510359B
Application number: CN202010205560.6A
Authority: CN
Inventors: 陈春华; 王志伟; 王世杰; 唐文正; 张文萍; 蔡元博; 袁彩蝶; 刘增辉; 马东祥; 陈西洋; 李东东; 吕向峰; 侯杰
Original assignee: Xuchang Zhongkesennirui Technology Co ltd
Current assignee: Henan Senior Electric Co ltd; Xuchang Zhongkesennirui Technology Co ltd
Priority date: 2020-03-23
Filing date: 2020-03-23
Publication date: 2022-03-11
Anticipated expiration: 2040-03-23
Also published as: CN111510359A

Abstract

The invention relates to a low-delay end-to-end communication method based on a CAN bus, which comprises the following steps: connecting a plurality of spacer layer devices with a CAN communication gateway through a CAN bus; the CAN communication gateway is connected with external equipment through a low-delay PHY Ethernet port or a 5G module; the low delay is a connection with microsecond level delay; when the communication is carried out between the bay level equipment and the CAN communication gateway, the method of automatically converting priority or intelligently adjusting the CAN load rate is adopted, so that the communication delay is less than 5 ms. The invention is suitable for a standard CAN bus hardware bottom layer protocol, a standard protocol is customized aiming at an application layer, the characteristics of low time delay and end-to-end communication are realized by embedding CPU software and hardware optimization, and the problem of high-speed data communication of the last kilometer communication CAN be solved.

Description

Low-delay end-to-end communication method based on CAN bus

Technical Field

The invention relates to the technical field of electronics, in particular to a low-delay end-to-end method suitable for realizing one of 5G core technologies through a CAN bus.

Background

With the development of new technologies such as industrial internet, internet of things technology, 5G technology, artificial intelligence and the like, the requirement on data transmission of intelligent equipment in the field of electric power energy is higher and higher, the current 5G suppliers in China are Hua and Zhongxing companies, public network construction is solved, low time delay and end-to-end communication are one of important indexes of 5G technical indexes, 5G provides end-to-end time delay requirement of millisecond level, the end-to-end time delay is 1ms under ideal conditions, and the typical end-to-end time delay is about 5-10 ms. The technical indexes of low time delay and end-to-end are one of the important indexes for realizing the control of the electrical industry and the interconnection and intercommunication of the industry. The method aims at realizing the new technology application of 'last kilometer communication' of the power secondary equipment, especially aims at the interconnection and intercommunication of the electrical equipment terminals, and does not provide a solution for realizing the application of the technical characteristics of 'low time delay and end-to-end'. "4G changes life, 5G changes the world", and 5G really changes the world only if the change is industrial application and really is implemented in industry. At present, industrial control is still mainly based on DCS, the main reason is that field industrial control needs low-delay signal acquisition and rapid decision execution, part of buses do not meet the characteristic of low delay at present, and even if 5G infrastructure channels reach the characteristic of low delay, the communication of the last kilometer cannot solve the problem of low delay, and the communication can become a technical bottleneck.

The characteristics of low time delay and end-to-end are transmitted to a digital instrument, a low-voltage measurement protection device, a motor protector, a high-voltage microcomputer protection device and the like through the communication of the last kilometer, and each electric equipment is added with a 5G module to realize the characteristics of low time delay and end-to-end. Each terminal is added with a 5G module, from the economic cost analysis, the price is currently 999 yuan for 5G industrial module MH5000, most industrial internet manufacturers buy 5G modules and embed the 5G modules into related products, and for a power digital instrument or a microcomputer protection device with the market price of only hundreds yuan to thousands of yuan, the 5G industrial module is added, so that the characteristics of 5G 'low time delay and end-to-end' are realized, the economic cost is too high, and the popularization is extremely difficult. Each terminal device is added with a 5G module, and analysis is performed from a technical level, so that the difficulty is high, and unreliable factors are in the terminal device. According to our field experience, many distribution equipment are installed in basements or remote factories, sometimes there is no signal when a call is made, 5G is higher in frequency than 4G signal, shorter in wavelength, poorer in penetration, relatively poorer in coverage capability, and more difficult to cover 5G signal.

The solution of the communication field bus of the last kilometer is various, and the current industry manufacturers have the existing solutions: RS485 communication, industrial Ethernet technology, wireless NB-IOT and LoRa, PROFIBUS-DP, Hua is PLC-IoT (Power line Carrier), DeviceNet and other field buses. These field buses all solve the communication problem, but for the 5G feature: low latency, end-to-end communication, is not mentioned nor is there a solution. Although the data volume transmission of the industrial ethernet can be guaranteed, the equipment cannot be connected in parallel with one communication line on site, so that the industrial ethernet has many nodes, small data volume, high wiring cost and high secondary equipment cost. PROFIBUS-DP and DeviceNet are expensive to use and are ecological communication platforms established by Siemens Germany and Rockwell USA, without proprietary intellectual property rights. The wireless NB-IOT and LoRa communication aims at the problems of complex electromagnetic environment of industrial field and weak signal of telecommunication service provider, aims at industrial control, is unreliable and is suitable for similar electric power meter reading occasions. Hua is PLC-IoT (Power line Carrier) and Hua is to provide a solution for solving the communication of the last kilometer, but the product supply information of the world is not available.

Disclosure of Invention

The invention aims to solve the problem of low-delay and end-to-end communication of last-kilometer communication, realizes the functions of low delay and end-to-end communication through a CAN bus, and solves the problem that the low delay of 5G Internet of things equipment is transmitted to an electric power equipment execution layer, the CAN bus has the characteristic of low delay, and the data transmission delay of a CAN bus protocol layer is less than 5 ms. Meanwhile, the electric power secondary equipment has the end-to-end communication capability, can realize interconnection and intercommunication among devices, quickly build a distributed artificial intelligence system, and achieve a centralized, quick and low-cost control cluster idea.

The invention provides a low-delay end-to-end communication method based on a CAN bus, which comprises the following steps:

connecting a plurality of spacer layer devices with a CAN communication gateway through a CAN bus; the CAN communication gateway is connected with external equipment through a low-delay PHY Ethernet port or a 5G module; the low delay refers to microsecond-level delay;

when the communication is carried out between the bay level equipment and the CAN communication gateway, the method of automatically converting priority or intelligently adjusting the CAN load rate is adopted, so that the communication delay is less than 5 ms.

Further, the method for automatically converting the priority comprises the following steps:

firstly, according to the transmission data characteristics, the device divides the function codes ID 24-ID 28 into 15 priorities of 1-15 according to the priorities; according to the function requirements, the function codes are different, no matter the address of the node is high or low, the fault event data with the highest priority is transmitted firstly, if a plurality of devices send fault events at the same time, the ID 16-ID 23 are address codes, and the node with the smallest address is transmitted firstly;

the interlayer equipment uplink data has a priority automatic conversion function, if the low-priority data on the CAN bus is still not transmitted for 4 times and waits for 1ms after the low-priority data is not transmitted, the interlayer equipment uplink data has the highest priority position, namely ID29, after the position of '1' is set to '0', the interlayer equipment uplink data has the highest priority, and the data is transmitted when the data is transmitted for the 5 th time or the 6 th time.

The interlayer device transmits data at most, has the lowest priority, and has the highest priority of the 'end-to-end' and 'gateway downlink' data, but has less data volume, so the two data transmissions do not have the priority reversal function.

Further, the method for intelligently adjusting the CAN load factor comprises the following steps:

firstly, the communication gateway has a load rate statistical function, when a wiring design system is applied in engineering, the capacity of bus nodes is adjusted in real time according to the conditions of the average load rate and the limit load rate of a bus, the number of the nodes is adjusted according to data parameters, background transmission frequency measures are adjusted, and the load rate of the bus is ensured to be below 30%;

secondly, the communication gateway automatically adjusts the data transmission frequency of the spacer layer equipment according to the load rate condition, the data of the spacer layer is updated within 1-2 seconds aiming at the remote measurement data transmission, if the load rate is higher than a preset value, the communication gateway suspends the remote measurement data transmission, and the data is transmitted to the background within 10 seconds;

finally, automatically adjusting a sudden change threshold of active transmission of telemetering data, wherein the sudden change threshold refers to a preset value of percentage of fluctuation, for example, if a rated value is 100V and a sudden change is set to be 1%, namely, a voltage value is greater than 101V or less than 99V, data can be transmitted, interlayer equipment remotely measures data transmission, the data are actively uploaded according to the sudden change threshold, a communication gateway transmits an instruction according to the load condition, the automatic uploading data transmission rule of the interlayer equipment is modified, and the sudden change threshold of the telemetering data is improved; if the data fluctuation is lower than the set threshold condition, the communication gateway automatically accounts the transmission time interval of each device, and if the situation that the data is not transmitted in 60 seconds after the remote measurement of the bay level is found, the communication gateway actively telemeters the data to the bay level once.

Further, the method for calculating the load rate of the CAN bus comprises the following steps:

the communication gateway adopts unfiltered CAN bus data, namely the communication gateway receives all CAN bus data, after receiving one frame of data each time, a CAN chip enters interruption and reads received data after entering interruption, after the CAN receives the interruption, the length of the received data is calculated, 1 interruption is calculated according to 156 bits, the interruption times are calculated by using a global variable, a timer is used for calculating the common interruption times within 10 seconds, and the load rate is calculated according to a 10-second period.

Furthermore, the CAN bus adopts a non-destructive bus arbitration technology of carrier sense multiple access/collision detection, when the nodes of the spacer layer equipment simultaneously send information to the bus, the nodes with lower priority CAN actively quit sending, the nodes with higher priority continue to transmit data without being influenced, and the bus arbitration time is saved; after the transmission of the data with high priority is finished, the node with lower priority actively sends the data again; and the data transmission priority on the CAN bus is determined according to the ID number, the smaller the ID value on the bus is, the highest priority is obtained, the ID is zero, the priority is the highest, all 29 bits are 1, and the priority is the lowest.

The downlink ID code of the communication gateway is 1-255, namely the spacer layer equipment address;

the end-to-end interconnection and intercommunication of the spacing layer equipment adopts the ID codes of 257-511, namely the spacing layer address + 256; the ID numbers of the uplink communication gateway data of the spacer layer equipment are all larger than 1677216, namely 0x1000000 in hexadecimal, the transmission quantity of the spacer layer data is maximum, the priority of the downlink protocol of the communication gateway is set to be highest, the transmission order of the end-to-end is set to be next to the transmission order, and the priority of the uplink protocol of the spacer layer is set to be lowest; in order to ensure that nodes with lower priority in an uplink protocol of the spacer layer can transmit to the communication gateway, the spacer layer can automatically change the priority according to the transmission times of the nodes, so that lower data of the nodes are transmitted, and the characteristic of low delay of all the nodes is achieved.

Further, a mask mode and an identifier list mode of the CAN hardware controller are used, each mode is provided with a receiving cache area mailbox, and interrupts are received;

the identifier list mode realizes low-delay data forwarding between the communication gateway and the equipment, the communication gateway issues a data command, only one equipment layer with a matched address receives the data command, and the data command enters FIFO 0 hardware for interruption;

the mask mode realizes end-to-end communication between the devices, and is 257-511, namely, the device address +256 coding mode realizes data reception between the devices, and after receiving the data, the data enters FIFO 1 for hardware interruption.

Further, the spacer layer receives the data ID code description of the communication gateway:

the interlayer equipment receives data and adopts an identifier list mode, and the ID number is completely consistent with the address of the interlayer equipment; the ID number range is 1-255, the spacer layer filtering ID number is the same as the equipment address, each equipment address number on a bus is unique, the spacer layer filters through the address, the fact that the ID code of downlink data of the communication gateway is completely the same as the equipment layer address CAN be received, the received data cache uses the first FIFO 0 in an STM32 chip, the CAN hardware acceptance screening device adopts 0-7, the first FIFO is interrupted in the chip, the ID number is consistent with the own address, and the received data enters the chip for interruption.

Further, the spacer layer device uplink protocol is as follows:

the interlayer equipment uplink to the communication management gateway transmits data information by using a 29-bit ID code, wherein the 29-bit ID code means as follows: the device comprises a priority ID29, function codes ID 24-ID 28, address codes ID 16-ID 23 and identification protocol analysis data codes ID 0-ID 15, wherein the range of the function codes is 1-15, and the range of the address codes is 1-255;

the ID numbers of the uplink communication gateway data of the bay level equipment are all larger than 1677216, namely 0x1000000 hexadecimal, the communication gateway does not filter data, the bus data CAN receive the data, the communication gateway non-filtering data mode is to ensure the intercommunication between the bay level equipment and the communication gateway, and the communication gateway CAN receive all ID number data on the CAN bus on the bay level.

Further, the "end-to-end" communication between the bay level devices is as follows:

each interval layer device can be provided with a logic pressing plate, a trigger, an executor and delay time, wherein the trigger is that the interval layer device detects whether the opening amount DI, the protection logic control and the programmable control of the device per se accord with the logic setting or not, once the logic condition is met, data is sent to a bus by using an end-to-end communication format according to a mask mode, other interval layer devices are set as executors, after the executors are set, the device receives the data, and the sender sends the data with the same meaning as the executor setting, and then relay output or transmission output is executed.

Further, the "end-to-end" communication ID code between the spacer layer devices is as follows:

the interlayer equipment communicates with each other, and a mask mode is adopted to ensure that the interlayer equipment can send broadcast commands;

the ID mask is 256-511, the unique address of the bay level equipment is 1-255 plus 256, and the ID code is 257-511;

the 'end-to-end' coding format adopts address codes plus 256, so that the 'end-to-end' data transmission ID numbers of more than 2 buses are prevented from being identical;

the communication of the spacing layer equipment is end-to-end, the CAN hardware acceptance screener is 8-13, the data cache adopts a second FIFO 1 in an STM32 chip, the ID number coding is 257-511, all the spacing layer equipment CAN receive data and enter the second FIFO in the chip for interruption; and if the pressing plate is put in, a processing program is entered, and if the pressing plate is not set, the data is discarded and not executed.

Further, the communication gateway receives the spacer layer device ID code as follows:

the communication gateway receives data and adopts a non-filtering data mode, so that mutual communication between the spacer layer equipment and the communication gateway is ensured, the communication gateway CAN receive all ID number data on a CAN bus on a spacer layer, the communication gateway does not filter the data, and the bus data CAN receive the data;

the communication gateway sends the ID code description of the spacer layer equipment:

the downlink ID is coded by 1-255, 1-255 actually are the address of the bay level equipment, the communication gateway and the bay level equipment, an identifier list mode is adopted, the downlink data of an application layer is guaranteed, only one equipment receives the downlink data, other equipment does not enter the interruption, and the efficiency of receiving the data by the bay level is high.

Has the advantages that:

1. the invention is suitable for a standard CAN bus hardware bottom layer protocol, a standard protocol is customized aiming at an application layer, the characteristics of low time delay and end-to-end communication are realized by embedding CPU software and hardware optimization, and the problem of high-speed data communication of the last kilometer communication CAN be solved.

2. The scheme that the communication gateway forwards the data of the interlayer power secondary equipment is adopted, the economic cost is acceptable, the 5G communication gateway is placed in a wide place or an antenna is additionally arranged to solve the problem of reliability of 5G signal coverage, and the method can be rapidly popularized from the economic cost and the technical cost.

Drawings

FIG. 1: the system framework topology of the invention;

FIG. 2: the invention relates to a communication gateway hardware frame diagram;

FIG. 3: CAN communication hardware frame diagram.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments, and all other embodiments obtained by a person skilled in the art based on the embodiments of the present invention belong to the protection scope of the present invention without creative efforts.

According to one embodiment of the invention, based on the technical problems, 60-100 interlayer power devices are managed by 1 communication gateway, external communication forwarding CAN be realized by using industrial Ethernet transmission or 5G module transmission, the interlayer power devices are communicated with the communication gateways and CAN buses are adopted for communication, and low delay and end-to-end characteristics are realized on the CAN buses and between the interlayer devices and the communication gateways.

The system comprises a spacer layer, a communication layer and an application layer;

the interval layer and the communication layer adopt CAN buses, CAN interfaces are adopted by the interval layer and the communication layer, and an Ethernet interface and a 5G communication module are adopted by an external outlet of the communication layer. The Ethernet interface adopts a low-delay PHY, the 5G communication module adopts an MH5000 industrial module, and the system background can select the Ethernet or 5G module interface to realize low-delay communication.

The spacer layer equipment comprises electric secondary element equipment such as a motor protector, a digital instrument, a low-voltage measurement protection device, high-voltage microcomputer protection and the like. And the equipment layer equipment adopts STM32 with CAN hardware microprocessing. As the software and hardware ecology of the semiconductor CPU chip of the ideological method are consistent, the following chips STM32F103, STM32F407, STM32F429, STM32F302 and the like are adopted according to different requirements of products.

The interlayer equipment completes self power grid data acquisition, liquid crystal display, user operation, serial port communication and DI/DO control. Each component device is provided with a CAN communication interface which accords with a communication protocol of a Controller Area Network (CAN) bottom layer, and an application layer protocol accords with the CAN communication protocol set by the invention.

The interlayer equipment adopts an embedded operating system and adopts C language programming to carry out system management on various tasks. The spacer layer equipment adopts the concept of 'edge calculation', and the data active uploading, remote measuring, remote signaling, remote control data and protocol matching work is realized by element equipment.

The communication layer equipment comprises a CAN-to-Ethernet communication gateway, which is referred to as a CAN communication gateway for short, and is shown in fig. 2, the CAN communication gateway adopts an STM32F429 chip by adopting an ideogram, and the CAN communication gateway is responsible for transferring CAN data to an Ethernet interface or transferring CAN to 5G wireless communication for external background communication. .

The CAN communication gateway comprises 2 paths of CAN interfaces, 1 path of 100M Ethernet interfaces and 1 path of 5G outlets.

An STM32F429 chip is internally integrated with a MAC chip, and a low-delay PHY 88E1510 is externally adopted, wherein the chip is a special low-delay PHY for industrial Ethernet. The scheme is guaranteed to have a low-latency characteristic from a hardware characteristic.

The 5G wireless communication adopts an HM5000-31 industrial module, the core of the industrial module adopts a Huazhi Ba Long 5000 chip, and the core devices comprise a main chip, a PMU, a radio frequency and the like which are completely independently controllable; the NSA/SA dual mode is supported, the industry client is helped to flexibly access different 5G mode networks, and the Chinese 5G SA network construction is supported; the method supports single-core full-mode, is fully compatible with 2G/3G/4G/5G, directly synchronizes the 5G network coverage rhythm, and protects the investment of client equipment. The downlink speed is up to 2Gbps, the uplink speed is up to 230Mbps, and the high bandwidth requirement of industrial application is met; the working temperature range is as wide as minus 40 ℃ to 85 ℃, and high-reliability devices and industrial unique design are adopted, so that the method is suitable for diversification of industrial environment; the microkernel adds a double security mechanism of TrustZone, so that the industrial environment is really safe and reliable to use; the self-contained high-performance application processor has the advantages that the calculation capacity reaches 14400DMPIS, and the hardware interface with 18 types can fully meet the interface requirement of industrial equipment.

The STM32F429 chip and HM5000-31 communication adopt dual-interface communication, including serial ports and SPI buses, adopt dual-communication hardware design, in order to verify the communication feasibility fast, the test adopts high-speed serial ports to test earlier stage, and the serial ports baud rate adopts 115200 bps. In order to ensure lower time delay of the chip and the 5G module, a high-speed SPI bus is adopted.

The STM32F429 chip has a 2-way internal CAN controller, and the external device used is TJA1050, and the TJA1050 is an interface between a Controller Area Network (CAN) protocol controller and a physical bus.

The CAN communication gateway adopts an embedded operating system, adopts C language programming and adopts an open source lwip protocol as an Ethernet communication protocol.

The communication background is transmitted to the communication gateway by adopting 5G equipment, 5G has a low time delay characteristic, even if a serial port is adopted to communicate with a 5G module (HM5000), the serial port baud rate reaches 115200, 0.078ms is needed for transmitting one byte of data, and 0.78ms is needed for transmitting 10 bytes of data. By using the higher-speed SPI bus, the bus frequency can reach 36M, and the chip SPI bus is provided with DMA, so that the data exchange transmission time interval between the chip and the HM5000 is shorter.

If the communication background adopts Ethernet communication, the STM32 chip has internal DMA, and the hardware PHY 88E1510 has faster data conversion speed, and ensures low delay from the hardware.

The communication gateway and bay level CAN hardware is as follows:

the communication gateway and the interlayer device realize low-delay end-to-end communication by using a CAN hardware mask mode and an identifier list mode.

The CAN controller CAN employ both a mask mode and an identifier list mode. The mask mode realizes the end-to-end communication of the spacer layer equipment; the identifier list mode realizes the communication of the communication gateway and the interlayer equipment with low time delay.

There are three current CAN underlying standard protocols: CAN-FD, CAN2.0A and CAN2.0B. Since the CAN-FD standard is released soon, the underlying protocol of the scheme adopts the CAN2.0B standard. The CAN2.0B standard employs a 29-bit ID code + 8-byte data transmission, and the ID codes are hereinafter referred to as CAN2.0B standard 29-bit masks.

In the mask mode, an identifier register is associated with the mask register to indicate which bits of the ID code "must match" and which bits are "don't care".

In the identifier list mode, the mask register is used as an identifier register. All bits of the incoming ID code must match the bits specified in the filter register.

The invention defines the protocol of the CAN communication application layer, which is the core rule established by the invention, namely three communication protocols of communication gateway downlink protocol, spacer layer equipment uplink protocol and end-to-end communication between spacer layer equipment. The spacer layer device adopts a method of combining a mask mode and an identifier list mode, and the communication gateway adopts an unfiltered data mode.

The spacer layer equipment uplink to the communication gateway ID code description:

according to one embodiment of the present invention, the data ID numbers of the spacer layer devices uplink to the communication gateway are all greater than 1677216(0x 1000000). The 29-bit ID of the bay level device is divided into a priority code (ID29), a function code (ID 24-ID 28), an address code ID 16-ID 23, and a protocol resolution data code ID 0-ID 15 in the identifier mode.

The interval layer receives the ID code description of the communication gateway data:

the spacer layer device receives data, and the ID number must be completely consistent with the spacer layer device address in an identifier list mode. The ID number range is 1-255, the filtering ID number of the spacing layer is the same as the equipment address, and the address number of each equipment on one bus is unique. The interlayer passes through address filtering, guarantees that communication gateway downlink data ID code and equipment layer address are the same CAN receive, and the received data buffer memory uses the inside first FIFO 0 (shown in figure 2) of STM32 chip, and CAN hardware acceptance screening ware adopts 0 ~ 7 (shown in figure 2), and the chip is inside to have first FIFO to interrupt, and the ID number is unanimous with own address, gets into the chip interrupt.

The communication gateway receives the ID code description of the equipment in the interval layer:

the communication gateway receives data in a non-filtering data mode, mutual communication between the spacer layer equipment and the communication gateway is guaranteed, and the communication gateway CAN receive all ID number data on the CAN bus on the spacer layer. The communication gateway does not filter data, and the bus data can receive the data.

because the downlink commands of the communication gateway are more and the downlink data volume is not large, the downlink ID adopts 1-255 codes, and 1-255 is actually the spacer layer equipment address. The communication gateway and the interlayer device adopt an identifier list mode to ensure that the downlink data of the application layer is received by only one device, other devices do not enter the interruption, and the efficiency of the interlayer receiving data is high.

Description of "end-to-end" communication ID encoding between spacer layer devices:

the interlayer equipment can realize the mutual communication between the equipment, and a mask mode is adopted to ensure that the broadcast command can be sent between the interlayer equipment.

The ID mask can pass verification by using 256-511 (0x 0000100-0 x000001FF), the device layer unique address (1-255) is added with 256, and the ID code is 257-511.

The 'end-to-end' coding format adopts address codes plus 256, in order to prevent that the ID numbers of the 'end-to-end' data transmission of more than 2 buses are identical, because 2 devices on one bus send the data with the same ID number at the same time, data transmission errors occur, and the transmission efficiency is influenced.

The communication of the interval layer equipment is end-to-end, the CAN hardware acceptance filter is 8-13, the data buffer adopts a second FIFO 1 (shown in figure 2) in an STM32 chip, the ID number coding is 257-511, and all the interval layer equipment CAN receive data and enter the second FIFO in the chip for interruption. Because one device in the spacing layer sends data, all devices on one bus receive the data, whether the data is executed or not needs to be judged whether the devices are set to be put into execution pressing plates or not, if the pressing plates are put into the execution pressing plates, a processing program is started, if the pressing plates are not set, the data are discarded and are not executed, and whether the end-to-end communication data are effectively realized by software judgment or not.

Regarding the end-to-end data transmission, the control is generally executed, the data volume is small, the data is not frequently transmitted, the broadcast transmission is adopted, and the software implementation judgment shielding mode does not occupy too many computing resources of the spacer layer. Because the application property of the decentralized distributed artificial intelligence system is determined, the data transmission is less, data is transmitted to a plurality of devices at the same time, generally, data acquisition and data logic processing of each node are all calculated by the acquisition node, and after the operation of the acquisition node is finished, other devices are only informed to execute relay action information.

The process flow of the interval layer end-to-end communication is as follows:

see previous description for CAN "end-to-end" communication ID filtering data scheme.

The end-to-end characteristic of the CAN communication bus is realized, and besides a CAN hardware arbitration mechanism, data processing flow cooperation is required.

The CAN bus adopts a non-destructive bus arbitration technology of carrier sense multiple access/collision detection, when nodes send information to the bus at the same time, the nodes with lower priority CAN actively quit sending, and the nodes with higher priority CAN continue to transmit data unaffected, thereby saving the bus arbitration time. And after the data with high priority is transmitted, the node with lower priority actively sends the data again.

The above discussion is realized by using the hardware characteristic of the CAN bus, and the end-to-end communication is not realized by using the hardware characteristic only, and the end-to-end communication is realized by matching software. The data processing flow is as follows:

each bay level device may be provided with a logic pressure plate, trigger, actuator, delay time. The trigger is that the bay level device detects whether the own device start number (DI), the protection logic control and the programmable control meet the logic setting, and once the logic condition is met, the bay level device sends data to the bus by using an end-to-end communication format according to a mask mode. The other spacer layer equipment is set as an executor, after the executor is set, the device receives data, and the sender sends the data with the same meaning as the executor setting, and then the relay output or the transmission output is executed.

Each spacer layer device has: digital Input (DI), analog measurement (similar voltage and current), 4-20 mA signal acquisition, protection logic control and programmable logic functions. The device is also provided with an output device: and a relay outlet, which is a transmission (4-20 mA) outlet. The transmitting output can control the belt analog quantity control valve, the analog quantity servo motor, the DCS acquisition equipment and the like.

Simple control logic is added to the analog quantity and the digital quantity of the interlayer equipment, the logic control condition is satisfied, and the relay action or the transmission output (4-20 mA) of the other interlayer equipment CAN be controlled through the end-to-end characteristic of the CAN bus.

The trigger may have 3 logic settings: digital Input (DI) logic setting, protection logic remote linkage, programmable logic control.

The actuating mechanism is divided into 2 types: a relay (DO) output and a transmitting output (4-20 mA). The relay output may set a level or pulse pattern. And transmitting output, namely controlling the output of transmitting (4.00-20.00) and how much output the executor transmits and sets.

Digital quantity open (DI) logic control settings description:

TABLE 1 Digital Input (DI) logic setup

Protection logic remote linkage:

the general electric microcomputer protection device is used for controlling the protection logic pressing plate to be put in or taken out through a 'bit'. For example, bit0 represents overcurrent I-segment protection; bit2 represents overcurrent II stage protection; bit3 represents overcurrent segment III protection. If 0x03 is set, the protection investment of the I section and the II section is represented.

TABLE 2 protection logic remote linkage

And (3) programmable logic control:

the user arbitrarily selects the alarm analog quantity (voltage, current, power factor and the like), the alarm analog quantity is set to be larger or smaller than the alarm analog quantity, and after the alarm analog quantity reaches the design condition, other devices are controlled to output.

TABLE 3 programmable logic control

The CAN communication link realizes a low time delay processing flow:

as shown in fig. 1, for the topology of the whole system, the application layer has a "low latency" characteristic, and uses a low latency characteristic 5G module, and ethernet communication also uses low latency devices from the aspect of hardware as much as possible. 156 bits are transmitted at most by one frame of CAN data, if the baud rate adopts 250kbps, the transmission time of one frame is 0.624ms, when the system is designed, the optimal load rate of a bus is 30%, the data load rate of the worst case is not more than 70%, the transmission delay of the low-priority frame data is calculated to be not more than 2 frames at most, and 1 frame of transmission delay is added, the total consumed time of the data transmission on the bus is not more than 2ms, and the communication 'low delay' index of the CAN bus of the system is 5 ms. If the data with lower priority is not transmitted under the extreme condition, the software has the method of automatically converting the data priority and intelligently adjusting the bus load software, and the data can be transmitted within 5 ms.

The communication gateway and the interlayer device CAN communicate by adopting an ID filtering method, and the method for realizing data hardware shielding by communication between the communication gateway and the interlayer device has been discussed in detail above.

In the invention, except for the low-delay hardware characteristic of the CAN bus, the software is used for processing data and a method for automatically converting priority and intelligently adjusting the load rate of the CAN bus is adopted, so that the node data CAN be ensured to be transmitted within 5 ms.

And the data transmission priority on the CAN bus is determined according to the ID number, the smaller the ID value on the bus is, the highest priority is obtained, the ID is zero, the priority is the highest, all 29 bits are 1, and the priority is the lowest.

The downlink ID code of the communication gateway is 1-255 (spacer layer address); the ID codes adopted by end-to-end interconnection and intercommunication are 257-511 (spacing layer address + 256); the ID numbers of the uplink communication gateway data of the bay level equipment are all larger than 1677216(0x1000000), the transmission quantity of the bay level data is the maximum, other transmission data are small, and the priority is not required to be adjusted by software. Therefore, the communication gateway downlink protocol has the highest priority, the 'end-to-end' transmission priority is the second highest, and the interval layer uplink protocol has the lowest priority. In order to ensure that nodes with lower priority in an uplink protocol of the spacer layer can transmit to the communication gateway, the spacer layer can automatically change the priority according to the transmission times of the nodes, so that lower data of the nodes are transmitted, and the characteristic of low delay of all the nodes is achieved.

The interlayer uplink to the communication management gateway makes full use of the 29-bit ID code to transmit data information. The 29-bit code means priority (ID29), function code (ID 24-ID 28), address code ID 16-ID 23, and identification protocol analysis data code ID 0-ID 15. The range of the function code is 1-15, and the range of the address code is 1-255.

First, the device divides the function codes (ID 24-ID 28) into 15 priority levels in total according to the priority levels according to the transmission data characteristics. For example, the highest priority of the fault event is 1, the SOE priority of DI and DO is 2, the lowest priority of the telemetry data is set to 15, and so on according to the rule, the function codes are different according to the function requirements. That is, regardless of the address of the node, the failure event data with the highest priority is transmitted first, and if a plurality of devices simultaneously transmit failure events (when function codes are the same), IDs 16 to 23 are address codes, and the node with the smallest address is transmitted first.

The system of the invention is used for testing, the number of nodes and the data volume are transmitted, when the data bus load rate is lower than 30%, the data can be transmitted in time, if the bus load is higher, the ID data with lower priority can not be transmitted, for example, the telemetering event with the largest address on the bus can possibly cause the phenomenon that the data can not be transmitted in time. This occurs, and the device has the ability to modify the priority characteristics. Normally, ID29 is set to "1", and normally, data is transmitted with priority based on the function code. If the bus has lower priority and is not transmitted when the interlayer device transmits frame data, the interlayer device automatically calculates the number of times of transmission, if the bus is transmitted 4 times (delay 4ms) and is still not transmitted, the frame ID29 is set to be 0, the frame ID is the highest priority level in the interlayer, and the data is transmitted within 5 ms.

And finally, the data bus is in normal communication, the load rate of the data bus is guaranteed to be 30%, the load rate of the data bus is guaranteed to be 60% in a severe case, and the load rate is guaranteed to be lower than 70% in an extreme case, which is a basic condition that data can be transmitted out in 5 ms. The invention also designs intelligent adjustment measures aiming at the bus load rate:

firstly, the communication gateway has a load rate statistical function (introduced below an algorithm), when a wiring design system is applied in engineering, the capacity of bus nodes is adjusted in time according to the conditions of the average load rate and the limit load rate of the bus, engineering application personnel adjust the number of the nodes according to data parameters, adjust background transmission frequency and other measures, and ensure that the load rate of the bus is below 30% under the normal communication condition.

Secondly, the communication gateway automatically adjusts the unimportant data transmission frequency of the spacer layer according to the load rate condition. For example, for telemeasurement data transmission, the data of the interval layer is updated within 1-2 seconds, if the load rate is high, the communication gateway suspends telemeasurement data transmission, and the transmission of the background within 10 seconds of the data is guaranteed.

And finally, automatically adjusting the active transmission mutation threshold of the telemetering data. The interlayer telemetering data transmission is carried out, active uploading is carried out according to the mutation threshold, the communication gateway can transmit instructions according to the load condition, the interlayer automatic uploading data transmission rule is modified, and the telemetering mutation threshold is improved. For example, under normal conditions, the mutation amount threshold is 0.5% of the rated value, and the method can be increased by 1% or 2%, and the maximum value can be increased by 8%. If the mutation threshold is set to be too high and the data fluctuation is lower than the threshold setting condition, the communication gateway automatically accounts the transmission time interval of each device, and if the situation that the data is not transmitted in the interval layer telemetering measurement for 60 seconds is found, the communication gateway actively telemeters the data to the interval layer once.

The method for calculating the load rate of the CAN bus comprises the following steps:

as mentioned above, the communication gateway does not filter the CAN bus data, that is, the communication gateway CAN receive all the CAN bus data. After receiving a frame of data each time, the CAN chip enters interruption, and the received data is read after the interruption. The can2.b protocol transfers 8 bits of data, 156 bits of data are transferred in total, and one byte is less, namely 8 bits of data are reduced. After the CAN reception is interrupted, the reception data length is calculated, 92+8 × 8 being 156, and the number of data bits is theoretically calculated in accordance with this. Since 8 bits of data are generally transmitted in the present protocol, even if less than 8 bits of data, it is recommended to ignore them. The operation is reduced as much as possible in the chip interruption, 1 interruption is calculated according to 156 bits, the interruption times are calculated only by using a global variable, a timer is used for calculating the common interruption times in 10 seconds, and a load rate is calculated according to a 10-second period, for example, the baud rate of the communication gateway is 500kbps, 10000 interruptions exist in 10 seconds, the bus load rate is 10000 × 156/10/500000 is 31.2%, and the load rate is 31.2%.

The optimal data load rate of the CAN data bus is 30%, the parameter is provided for engineering users, and the engineering users adjust the number of nodes and the background data transmission frequency according to the load rate. Meanwhile, the communication gateway has the intelligent algorithms, when the load rate is higher than 60%, the data transmission rule is automatically adjusted, and if the load rate is lower than 30%, the original data transmission rule is adjusted.

The invention adopts a communication gateway forwarding scheme, has acceptable economic cost, solves the problem of reliability of 5G signal coverage by placing the 5G communication gateway in a wide place or additionally arranging an antenna, and can be rapidly popularized from economic and technical cost. Because the traditional field bus is adopted in the market, the low-delay and end-to-end communication are not provided, and the following two applications can be realized.

Application 1: the last kilometer of communication bus does not have the characteristic of low time delay, and the DCS control system still needs to be connected through DI or electrical hardwiring aiming at quick response to quickly execute control. The scheme has the characteristic of low time delay, can quickly execute control through the communication line, and reduces the ready wiring cost.

Application 2: by utilizing the end-to-end characteristic of the communication of the last kilometer, a distributed artificial intelligence system is rapidly created, and the centralized, rapid and low-cost control cluster idea is eliminated. The following illustrates the distributed artificial intelligence system characteristics:

for example, the workshop controls the start or stop of the fan and the dehumidifying equipment according to the temperature or humidity data so as to achieve the energy-saving or process target.

The design of a central control system, temperature measurement sensor equipment or humidity measurement equipment collects equipment data through a communication gateway, transmits a DCS background, the background compiles logic control through configuration software, and then sends an instruction to the communication gateway, the communication gateway sends an actuating mechanism again to execute, and the actuating mechanism controls a fan to start.

The design of the distributed artificial intelligence control system is much simpler, temperature measuring sensor equipment or humidity measuring equipment is collected, and through logical programming, the temperature or the humidity which is higher than the temperature or the humidity is directly sent to the actuating mechanism to start the fan. This design is simple and reliable, and complex control logic can also be solved by a simple and reliable setup.

The invention is suitable for the bottom layer protocol of standard CAN bus hardware, makes the standard protocol aiming at the application layer, realizes the characteristics of low time delay and end-to-end communication by embedding CPU software and hardware optimization, and CAN solve the problem of high-speed data communication of the last kilometer communication.

Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, but various changes may be apparent to those skilled in the art, and it is intended that all inventive concepts utilizing the inventive concepts set forth herein be protected without departing from the spirit and scope of the present invention as defined and limited by the appended claims.

Claims

1. A low-delay end-to-end communication method based on a CAN bus is characterized in that: the method comprises the following steps:

when the communication is carried out between the bay level equipment and the CAN communication gateway, a method of automatically converting priority or intelligently adjusting CAN load rate is adopted, so that the communication delay is lower than 5 ms;

the automatic priority switching method comprises the following steps:

the interlayer equipment uplink data has a priority automatic conversion function, if the low-priority data is sent for 4 times and still is not transmitted, waiting for 1ms after the low-priority data is not transmitted, the interlayer equipment uplink data has the highest priority position, namely ID29, and after the position of '1' is set to '0', the interlayer equipment uplink data has the highest priority, and the data is transmitted when the data is transmitted for the 5 th time or the 6 th time;

the method for intelligently adjusting the CAN load rate comprises the following steps:

finally, automatically adjusting a mutation threshold for active transmission of telemetering data, wherein the mutation threshold is a preset value of the percentage of the mutation, interlayer equipment remotely measures data transmission and actively uploads according to the mutation threshold, and a communication gateway can transmit instructions according to the load condition, modify the automatic uploading data transmission rule of the interlayer equipment and improve the mutation threshold of the telemetering data; if the data fluctuation is lower than the set threshold condition, the communication gateway automatically accounts the transmission time interval of each device, and if the situation that the data is not transmitted in 60 seconds after the remote measurement of the bay level is found, the communication gateway actively telemeters the data to the bay level once.

2. The CAN-bus-based low-latency end-to-end communication method according to claim 1, wherein: the method for calculating the load rate of the CAN bus comprises the following steps:

3. The CAN-bus-based low-latency end-to-end communication method according to claim 1, wherein: the CAN bus adopts a non-destructive bus arbitration technology of carrier sense multiple access/collision detection, when the nodes of the spacer layer equipment simultaneously send information to the bus, the nodes with lower priority CAN actively quit sending, the nodes with higher priority continue to transmit data without being influenced, and the bus arbitration time is saved; after the transmission of the data with high priority is finished, the node with lower priority actively sends the data again; the data transmission priority on the CAN bus is determined according to the ID number, the smaller the ID value on the bus is, the highest priority is obtained, the ID is zero, the priority is highest, all 29 bits are 1, and the priority is lowest;

the end-to-end interconnection and intercommunication of the spacing layer equipment adopts the ID codes of 257-511, namely the spacing layer address + 256; the ID numbers of the uplink communication gateway data of the spacer layer equipment are all larger than 1677216, namely 0x1000000 in hexadecimal, the transmission quantity of the spacer layer data is maximum, the priority of the downlink protocol of the communication gateway is set to be highest, the transmission order of the end-to-end is set to be next to the transmission order, and the priority of the uplink protocol of the spacer layer is set to be lowest; in order to ensure that the nodes with lower priority in the uplink protocol of the spacer layer can transmit to the communication gateway, the spacer layer can automatically change the priority according to the transmission times of the nodes, so that the data with lower priority can be transmitted, and the characteristic that all the nodes have low time delay is achieved.

4. The CAN-bus-based low-latency end-to-end communication method according to claim 1, wherein: using a mask mode and an identifier list mode of the CAN hardware controller, wherein each mode is provided with a receiving cache zone mailbox for receiving interrupts;

5. The CAN-bus-based low-latency end-to-end communication method according to claim 1, wherein: the spacer layer receives the ID code of the communication gateway data as follows:

6. The CAN-bus-based low-latency end-to-end communication method according to claim 1, wherein: the spacer layer device uplink protocol is as follows:

the interlayer equipment ascends to the communication management gateway and transmits data information by using 29-bit ID codes, wherein the 29-bit ID codes have the following meanings of priority ID29, function codes ID 24-ID 28, address codes ID 16-ID 23 and identification protocol analysis data codes ID 0-ID 15, the range of the function codes is 1-15, and the address codes are 1-255;

7. The CAN-bus-based low-latency end-to-end communication method according to claim 1, wherein: the "end-to-end" communication between bay level devices is as follows:

8. The CAN-bus-based low-latency end-to-end communication method according to claim 1, wherein:

the "end-to-end" communication ID code between spacer devices is as follows:

9. The CAN-bus-based low-latency end-to-end communication method according to claim 1, wherein: the communication gateway receives the ID code of the spacer layer equipment as follows:

the downlink ID is coded by 1-255, 1-255 actually are the address of the bay level equipment, the communication gateway and the bay level equipment, and an identifier list mode is adopted, so that the downlink data of an application layer is ensured to be received by only one equipment, other equipment does not enter interruption, and the efficiency of receiving the data by the bay level is improved.