CN113067761B

CN113067761B - Linear token data bus simulation platform based on OPNET

Info

Publication number: CN113067761B
Application number: CN202110292722.9A
Authority: CN
Inventors: 路辉; 马雨忻
Original assignee: Beihang University
Current assignee: Beihang University
Priority date: 2021-03-18
Filing date: 2021-03-18
Publication date: 2022-03-25
Anticipated expiration: 2041-03-18
Also published as: CN113067761A

Abstract

The invention discloses a linear token data bus simulation platform based on OPNET, which adopts three-layer modeling at a node layer, an application layer generates and sends a data packet according to a settable rate, a medium access control layer executes the core function of a protocol and comprises the functions of initialization, token application, logic ring establishment, token transmission, data message sending controlled by a timer, fault station ring withdrawing and new station ring entering, a physical layer sends data to a bus and receives bus data, and signals of bus collision and message sending completion are transmitted to the medium access control layer. The invention provides an analysis platform for the linear token data bus from the qualitative and quantitative angles, is very visual and clear, has good expandability and provides a more convenient tool platform for the performance research of the data bus serving an avionics system.

Description

Linear token data bus simulation platform based on OPNET

Technical Field

The invention aims at the simulation of the communication of a linear token data bus, and particularly relates to a platform which is built based on OPNET software and is used for simulating the linear token data bus.

Background

With the ever-increasing sophistication of the mission of avionics systems, the integration of avionics equipment requires the ability of the avionics data bus to efficiently provide commands and communications between a large number of subsystems. The efficient and reliable control of the cooperation between the various subsystems of an avionics device is an important basis for the efficient operation of avionics systems, and the essential point of the cooperation of the subsystems is the communication. Taking an aviation aircraft as an example, subsystems of the aircraft such as radar, navigation, external weapons and the like can be mutually connected and reliably communicated through a bus, so that the aircraft can flexibly complete various functions such as navigation, attack, danger avoidance and the like. Unlike civilian communication systems, which focus on speed, bandwidth and cost of communication, military communication systems focus more on reliability and require bus networks to have longer lifetimes in severe military environments.

Currently, the existing medium access technologies are mainly classified into two categories, namely random access technologies and controlled access technologies. Random access techniques have not been widely used on avionic buses due to their reliability limitations; controlled access techniques, however, have been successfully applied to military aviation data buses due to their high level of certainty and reliability.

The controlled access technology can be divided into two types according to the control mode, one is a centralized control method called a command response protocol, and the other is a distributed control method called a token passing protocol. Military standards MIL-STD-1553 and MIL-STD-1773 of the united states department of defense are both command response protocols. The popularity of the command response protocol does make the data bus highly deterministic and allows to prioritize the users, but it has problems with overall communication delays and the bus controller is a weak point of the protocol, which in case of failure can lead to a crash of the whole system, so the command response protocol still has certain disadvantages in terms of stability and lifetime.

The token passing protocol has the characteristics of both system stability and high data rate, so that the token passing protocol is gradually applied to military aviation data buses after the command response protocol is developed, the Society of Automotive Engineers (SAE) firstly makes a contribution in developing the token passing protocol, two protocols of a linear token data bus and a token ring bus can be applied to the aviation data bus, and finally experiments show that the performance of the linear token data bus is slightly superior to that of the token ring. The linear token data bus can realize the distributed processing of the bus data, and can also carry out priority sequencing on messages according to the requirements of the airplane, and the message priority can be realized by setting different token rotation timers, so that the messages with high priority can be ensured to have lower delay.

The bus protocol has very important theoretical value and potential application prospect in the field of aviation electronic buses and communication fields in China, at present, domestic engineering researchers in the field are dedicated to applying a linear token data bus to military aircraft systems in China to improve the communication efficiency of aviation equipment in China, and the performance research of the bus is the premise of practical application.

In China, the linear token data bus is not applied to actual airplane equipment at present, and many researchers research the bus protocol from the aspects of theory and communication performance, try to find the optimal bandwidth allocation scheme of the linear token data bus network, and research the priority mechanism performance of the linear token data bus under the conditions of different service loads and the like. Some researchers have conducted simulation research on the bus through a discrete-time simulation language such as simscript, but the description process through the programming language is very different, and it is difficult to visually display the simulation result. In view of this, the invention provides a linear token data bus simulation platform, which is built in OPNET software and provides a more convenient and intuitive way to understand the working mechanism of the linear token bus.

Disclosure of Invention

The invention builds a set of platform for simulating the linear token data bus based on OPNET software, and processes the delay of the bus protocol under different loads, the influence of the distribution of messages on the bus delay and the like through the simulation platform. The invention selects the animation display function during the operation by means of OPNET software, and can qualitatively simulate the working processes of logic ring initialization, message sending, token passing and the like of the bus; the bus performance can be quantitatively simulated by customizing the event handler and the statistical variable before running the simulation.

A simulation platform applied to the linear token data bus is established in an OPNET software environment, and the functional simulation of the linear token data bus is realized by compiling and establishing the platform through a ProtoC language. The invention is programmed in three layers of a network layer, a node layer and a process layer of OPNET software, selects the bus link with corresponding data rate, can adapt to simulation and research under various conditions, has good expandability and is easy to maintain and modify.

The invention relates to a linear token data bus simulation platform based on OPNET, which at least comprises a computer; the method is characterized in that: the simulation platform is characterized in that a common process collection unit (10) is arranged in an application layer, a queue process collection unit (20) is arranged in an MAC layer, and a bus transmission unit (30) and a bus receiving unit (40) are arranged in a physical layer;

the common process collecting unit (10) is used for enabling the application layer to be as oneCollecting data message packets generated at a fixed rate, and then transmitting the data message packets FL₁₀To a queue process collection unit (20) in the MAC layer;

bus receiving unit (40) for receiving a data stream FL on a linear token data bus_inSecond aspect is to flow data FL_inTransmitting to a queue process collection unit (20), a third aspect of the invention is to detect a conflict instruction MD₄₀Sending to a queue process collection unit (20);

the bus transmission unit (30) is used in the first aspect for receiving the transmission data flow FL output by the queue process collection unit (20)₂₀Second aspect the end of each frame transmission flag BS₃₀Output to a queue process collection unit (20), and a third aspect transmits a data stream FL₂₀Transmitting to a linear token data bus;

the queue process collection unit (20) is at least provided with a token control unit (20A);

queue process collection unit (20) for receiving data message packets FL₁₀Second aspect is the FL₁₀Storing the data into a message queue according to priority, transmitting the message by a token control unit (20A) according to a state transition rule, and receiving the received data flow FL output by a bus receiving unit (40) by a fourth aspect_inAnd conflict detection instruction MD₄₀Fifth aspect, the reception bus transmission unit (30) outputs an end-of-frame transmission flag BS₃₀Sixth aspect is to transmit a data stream FL₂₀To a bus transmission unit (30).

Compared with the prior art, the linear token data bus simulation platform based on the OPNET has the following advantages:

(1) the linear token data bus simulation platform is strong in adaptability based on OPNET software, different initialization parameters and simulation parameters can be set according to the actual requirements of researchers, the research content can include the influence of the sizes of different application layer data packets, the data packet sending rate, the packet sending interval time distribution, the symmetry of data distribution and the like on the end-to-end delay of the bus data packet, the influence on the setting of a timer and the like, the research result can be directly drawn for visual description, and the conditions of a plurality of different independent variables can also be operated at one time, so that the result analysis and comparison of different initialization parameters can be conveniently carried out.

(2) The parameters in the simulation platform are transparent to a user, compared with packaged data, the flexible modification of the simulation parameters is strong, the user can set various parameter values according to research requirements, and the research efficiency is greatly improved.

(3) Due to the layering and modularization simulation characteristics, all parts can be developed independently, if the requirement of more in-depth function modification on each module exists in the research process, modification can be directly carried out in the corresponding module, and the modules are not limited to each other, so that the expandability is high.

(4) The unique animation simulation function of the software can enable researchers to observe various working processes such as token passing and data passing of the linear token data bus very intuitively, so that the platform has certain advantages in both qualitative and quantitative aspects.

Drawings

Fig. 1 is a functional structure block diagram of the OPNET software-based linear token data bus simulation platform of the present invention.

FIG. 2 is a diagram illustrating a queue process structure according to the present invention.

Fig. 3 is a flow chart of the operation of a station of the present invention from start to finish.

FIG. 4 is a flow chart of the operation of a station applying for a token during a start-up phase of the present invention.

Fig. 5 is a flow chart of the operation of the present invention after an unsuccessful application for a token.

Fig. 6 is a flow chart of the operation of the station of the present invention after successfully applying for a token.

Fig. 7 is a flow chart of the operation of the present invention after a station that does not establish a complete logical loop receives a message.

Fig. 8 is a flow chart of the operation of the invention after a station having completed a logical loop receives a message.

Detailed Description

The present invention will be described in further detail and with reference to the accompanying drawings so that those skilled in the art can understand and practice the invention.

The invention designs a linear token data bus simulation platform which is based on OPNET software, completes platform construction in a ProtoC language and state transition diagram mode, and carries out gradual deep construction through a network layer module, a node layer module and a process layer module.

Referring to fig. 1, the key of the simulation platform of the present invention is the programming modeling of the node layer and the process layer. From the node model level, the functions inside a node need to be completed by three layers of architectures, namely an application layer, a Media Access Control (MAC) layer and a physical layer. The application layer is used for generating a data message packet according to a certain rate and transmitting the data message packet to the MAC layer for processing. The MAC layer is a core working layer of a protocol, and functions thereof include a series of non-application layer protocol functions such as receiving and analyzing data, transmitting data, generating a token, and the like. The physical layer is used for sending the data packet to the bus, and meanwhile, the transmitting unit and the receiving unit of the physical layer need to feed back information whether collision exists and whether the sending of the message is finished to the MAC layer, so that the MAC layer finishes corresponding state conversion according to the feedback information.

The invention describes the work function of each workstation by utilizing a three-layer architecture, the function of an application layer is to generate data packets according to a certain rate, and the time for starting to generate the data packets can be set by self. The arrows pointing from the application layer to the MAC layer represent the traffic data flow at the application layer. The application layer is only responsible for generating and sending data packets to the MAC layer and does not store data, so the application layer is a common process node. The queue process is realized as the most core part of the whole protocol, and comprises storing the packet transmitted by the application layer, initializing a logic ring, executing BIT, transmitting a token, transmitting a message according to a priority control mechanism and the like. The specific structure construction of the MAC layer is completed according to the step 2. The physical layer comprises a bus transmitter and a bus receiver and is responsible for transmitting data required to be transmitted by the upper layer of the physical layer to the bus and receiving data on any bus and transmitting the data to the MAC layer. In the figure, the red arrow pointing to the queue process by the transmitter represents the mark of the end of each frame of data transmission, and the medium access control layer judges and executes subsequent operations according to the mark of the end of transmission. The red arrow pointing to the queue process by the receiver represents that the receiver needs to transmit a signal whether a bus link has data collision to an upper layer, the signal has a very important role in the cold start stage of the bus, if collision occurs, each workstation resets a BAT timer and sends out an application token frame according to a protocol standard, and a bus transmitter and the receiver are a connection bridge of a bus protocol working mechanism and an actual bus.

Referring to fig. 1, in the linear token data bus simulation platform based on OPNET software of the present invention, a common process collection unit 10 is disposed in an application layer, a queue process collection unit 20 is disposed in an MAC layer, and a bus transmission unit 30 and a bus reception unit 40 are disposed in a physical layer.

The linear token data bus simulation platform based on the OPNET software is installed in a computer. A computer is a modern intelligent electronic device capable of automatically performing a large number of numerical calculations and various information processing at high speed in accordance with a program stored in advance. The lowest configuration is CPU 2GHz, memory 4GB and hard disk 10 GB; the operating system is windows 7 and above.

General process collecting unit 10

In the present invention, the common process collecting unit 10 is used for collecting the data message packet generated by the application layer according to a certain rate, and then collecting the data message packet FL₁₀To the queue process collecting unit 20 in the MAC layer.

Bus receiving unit 40

In the present invention, the bus receiving unit 40 is used in a first aspect for receiving data on a linear token data busData stream FL_inSecond aspect is to flow data FL_inTransmitted to the queue process collecting unit 20, and the third aspect sends a conflict detection instruction MD₄₀To the queue process collection unit 20.

Bus transmission unit 30

In the present invention, the bus transmission unit 30 is used in the first aspect for receiving the transmission data flow FL output by the queue process collection unit 20₂₀Second aspect the end of each frame transmission flag BS₃₀Output to a queue process collection unit 20, and a third aspect transmits a data stream FL₂₀To the linear token data bus.

Queue process collecting unit 20

In the present invention, the queue process collecting unit 20 is provided with at least a token control unit 20A. Queue process collection unit 20 is for receiving data message packets FL in a first aspect₁₀Second aspect is the FL₁₀Stored in a message queue according to priority, the token control unit 20A of the third aspect performs message transmission according to a state transition rule, and the receiving bus receiving unit 40 of the fourth aspect receives the received data flow FL output_inAnd conflict detection instruction MD₄₀Fifth aspect of the invention receives the end-of-frame transmission flag BS output from the bus transmission unit 30₃₀Sixth aspect is to transmit a data stream FL₂₀To the bus emitter unit 30.

Referring to fig. 2, a data message packet FL₁₀After being received by the queue process collecting unit 20, the messages are stored in the message queue according to the priority, and the number of the message queue is marked with: message queue MP with priority 0₀Message queue MP with priority 1₁Group message queue MP with priority 2₂Group message queue MP with priority 3₃. All the sorted message queues are entered into the token control unit 20A in a first-in first-out manner.

In the present invention, the message queue entering the token control unit 20A completes the transition state according to the state transition rules shown in fig. 3, 4, 5, 6, 7, and 8. In the transition between the respective states in fig. 3 to 8, the above or left side of the line is a transition condition, the below or right side of the line is an operation to be performed while performing the transition, and if there is no condition, the transition is automatically performed.

Referring to fig. 3, in the present invention, the initial state of sending a packet by the application layer is the Sinit state, when software is started (i.e., a start instruction F), the state enters the Swait state from the Init state, and when packet start information (i.e., a start packet instruction H) is received, the state enters the Ssend state, in which the packet is continuously sent to the MAC layer.

State transition from successful application token to waiting token

Referring to fig. 4, in the present invention, when software starts (i.e. start command F), the BIT state is entered from the Init state, the process of bus self-test execution is simulated by delaying for a period of time, then when BIT execution ends (i.e. delay time end command G in software), the application token frame is sent and the Jdg _ cll state is entered, and when bus collision occurs (i.e. collision command C), the application token frame is sent again in the Clm _ tkn state; when there is no bus collision, the state transitions directly to the Tkn _ gt state and a token frame is sent. If there is no conflict on the bus after the station entering Clm _ tkn state transmits the application token frame, the station acquires the token transmission right when the BAT timer times out (i.e., timeout condition a1), and enters Tkn _ gt state. After the token is sent, the state Wt _ tkn is entered.

The timer overtime condition instruction A comprises a BAT overtime condition instruction A1, a THT overtime condition instruction A2, a TPT overtime condition instruction A3, a RAT overtime condition instruction A4 and a TRT overtime condition instruction A5.

Unsuccessful application token to wait token state transition

Referring to fig. 5, in the present invention, for a station which does not obtain bus control during bus contention, that is, a station which does not successfully issue a token applying frame in the token applying phase, after receiving a signal on the bus, its state receives a message condition command B from Clm _ tkn state into Analyze, and analyzes the frame type and DA field address. If a token frame directed to the station is received (i.e., conditional instruction B11 is received), the token is sent and the Wt _ tkn state is entered. If no token frame is received (i.e., a conditional directive B2 or B3 is received) or the token frame is not directed to the station (i.e., a conditional directive B12 is received), the Wft _ pu state is entered.

The received packet condition command B comprises a received token frame condition command B1, a received application token frame condition command B2 and a received message frame condition command B3. The receiving of the token frame conditional instruction B1 further includes receiving a token frame conditional instruction B11 directed to the station, receiving a token frame conditional instruction B12 not directed to the station. B12 further includes token frame conditional instruction B121 sent by the station, and token frame conditional instruction B122 not sent by the station.

The state of the waiting token enters the state transition of continuing waiting or sending the message according to the received frame information

Referring to fig. 6, in the present invention, entering Wt _ tkn state after the token is sent, the TPT timer starts counting. If a message condition instruction B is received in the Wt _ tkn state, entering an Analyze state, firstly analyzing whether the received frame is a token frame, if the condition instruction is B1, entering a Jdg _ pkt _ slf state, judging whether the received frame is the token frame sent by the station in the state, if so, returning to the Wt _ tkn state if the received frame is the token frame which is sent by the station, if not, further judging whether the destination address of the token frame is the physical address of the station, if so, receiving the condition instruction B11, indicating that the frame addressed to the station is received, recording the address of the subsequent station, entering Rcrd _ suc _ addr, judging whether a message queue is empty, if so, receiving a condition instruction D1, sending the token and entering an Wff _ nm state, and if not empty, entering a Pass _ g state if not, receiving a condition instruction D2. And further judging that the destination address field is not the physical address of the station although the token frame is the token frame, namely, after the conditional instruction B122 is received, the subsequent station address is recorded and then the Pwrup _ idle state is entered.

The issue queue info conditional instruction D includes an issue queue empty conditional instruction D1, and includes an issue queue not empty conditional instruction D2.

State transition of non-established logical ring to established logical ring process

Referring to fig. 7, in the present invention, after receiving a message condition command B in a Pwrup _ idle state, an Analyze state is entered, and in this state, it is determined whether the message frame is a token frame, if a B1 condition command is received, a Jdg _ addr state is entered, and if a B2 or a B3 is received, a Pwrup _ idle state is returned. And judging whether the token address is the physical address of the station under the Jdg _ addr state, if so, receiving a conditional instruction B11, judging whether a message queue is empty, and if not, further receiving an instruction condition D2 and entering a Pass _ msg state. The Wff _ nm state is entered if the instruction condition D1 is further received. And (3) entering a Pass _ msg state from a Pwrup _ idle state, receiving a message sending ending instruction E after sending a frame of message, judging whether the THT timer is overtime, returning to the self state if the THT timer is not overtime, continuously sending the message, and entering a Wff _ nm state if the THT timer is overtime, namely receiving a conditional instruction A2 or a message sending queue is empty, namely receiving instruction information D1.

State transition for sending messages after a logical ring is established

Referring to fig. 8, in the present invention, a station entering Wff _ nm state enters Analyze state after receiving message condition instruction B, determines which type of packet belongs to, receives condition instruction B1 if it is a token frame, enters Jdg _ pkt _ slf state, returns to Wff _ nm state if it is not, that is, receives condition instruction B2 or B3, returns to Wff _ nm state if it is a token directed to itself in Jdg _ pkt _ slf state, receives condition instruction B11, enters Cancel _ TPT state, determines whether to enter message sending state according to receiving D1 condition instruction or D2 condition instruction, and returns to Wff _ nm state after entering message sending.

In the invention, the bus serving an avionics system and simulated by applying OPNET software comprises the functions of initializing an application layer packet sending layer and an MAC layer, executing self test, detecting conflict, sending a token, sending a message according to priority, enqueuing the message, analyzing data, exiting a fault station and entering a recovery station.

The packet sending function of the application layer is completed by setting self-interruption at different time points, and different packet sending starting times and packet sending intervals can be set according to research needs.

When the MAC layer is initialized, each Timer includes five kinds of seven timers, i.e., BAT (Bus Activity Timer), TPT (Token Passing Timer), RAT (Ring acceptance Timer), TRT (Token Rotation Timer), and THT (Token Holding Timer), where the TRT Timer includes three timers, i.e., TRT1, TRT2, and TRT 3. Setting some mark information which needs to be used subsequently; setting test time when self-test is executed and describing the end of the test by using self-interruption; the conflict detection is realized by transmitting conflict information to the MAC layer through the physical layer and through 'startwire'; the token sending needs to specify the field and length of each type of frame through a frame format editor, then set each field value through ProtoC language in the MAC layer and send the set field value to a physical layer bus transmitter; the bus sets the transmission according to the priority on the mechanism of data packet transmission, controls the priority by using 3 TRT timers, and controls the time of the token staying on a certain subsystem by the THT timer; setting different message queues for messages with different priorities, enqueuing the messages sent by an application layer through a First Input First Output (FIFO) mechanism, and dequeuing accumulated data at proper time; after the logical ring is established, if a station in the ring fails, the ring establishment operation is transferred from a front station of the failed station, the physical address of a subsequent station is added from the failed station and traverses backwards, if the subsequent station traverses to the station in the original logical ring, the traversal is stopped, otherwise, the next station starts to traverse backwards according to the principle that the physical address of the subsequent station is gradually increased as the physical address of the current station; the recovery station is controlled by a RAT timer and is embodied in software in a mode of setting self-interruption.

The network layer module needs to embody the topological structure of the bus, the parameters of each station on the bus and the data rate of the bus. A bus is the medium of signal transfer. The core construction of the protocol flow is that in a node layer model, the node layer model is further subdivided and divided into an application layer module, an MAC layer module and a physical layer module. Table 1 shows the division of labor of the three-layer modules, and the detailed implementation of the three modules is described in detail after table 1.

Table 1 each module of node layer

The application layer module is responsible for generating a data packet and sending the data packet to the MAC layer module at a certain data rate, and the application layer module in the OPNET software is composed of three state models, which can only be one of the three states at any time, namely, an initial state, a waiting state and a data sending state, that is, an application layer state SYY ═ Sinit, swap, and Ssend }, as shown in fig. 3.

Table 2 application layer states and functional description

Status name	Chinese semantics	Detailed Description
			Sinit	Initialization	State of application layer when software has not started
Swait	Wait for	After software is started, waiting for message sending state
			Ssend	Sending	Message persistent transmission state

The jumping relation among the three states is that when a program is started, a starting interrupt is generated, the state is switched from the Sinit state to the Swait state, in the state, after the time of Tstart seconds, the state enters a send Send state, one frame of data is sent to the MAC layer for packaging every Tgap seconds, when the Tgap time is over, software generates a send message interrupt, the send message is over, and the state returns to the Send state after the send is over.

The MAC layer module is responsible for receiving the data packets of the application layer and storing the data packets into the message queue according to the priority condition of the data packets (as shown in fig. 2). And when the node layer module receives the data packet received by the physical layer receiver and analyzes the data packet to find that the data packet is a token frame, the node layer module sends the data according to a protocol message sending mode. In addition, the MAC layer module also has the functions of establishing a logic ring, generating a token frame, retreating the ring when a fault occurs and entering the logic ring at a proper time. The above functions are achieved by switching between different states at the MAC layer.

Table 3 State description

In the process of executing the linear token data bus protocol, the normal working phase after the bus power-on phase and the logic ring are well established. The process of powering up the bus is called a cold start process, in which each subsequent parameter is initialized first, and the initialized object has the value of each timer and some flag bits. These flag bits are used in subsequent phases of operation of the bus protocol. And after the initialization is finished, each workstation performs built-in self-test, and after the self-test is finished, each workstation initializes a BAT timer. The station whose BAT timer has timed out first will send out the application token frame. At this time, more than one station may send out the application token frame, so the physical layer receiver will send a signal to the MAC layer whether there is a conflict, if there is a conflict, the station with timeout BAT will initialize the BAT timer again, and the station without timeout will enter the quiescent state. Because the time reference of BAT reinitialization is consistent at this moment, the station BAT value with smaller physical address is smaller according to the protocol regulation, and the station BAT value is overtime first, the station BAT sends a token applying frame and obtains a first token, and the operation of initializing the bus logic ring is started.

The method for initializing the logical ring is to search in a mode of traversing each workstation in an incremental way according to the physical address, and if the same workstation is visited twice and no response is obtained within the time of TPT, the workstation is skipped to visit the next workstation. If the accessed workstation sends a token to search for a subsequent station within the time of TPT, the previous station enters a static state. When traversing to the maximum allowed number of stations 128 (physical address 127), the traversal will continue with incrementing starting from physical address 0 until traversing to the station that initiated the initialization of the logical ring, at which point the initialization of the logical ring ends.

The function from cold start to initialization of the logic loop is the process of transmitting a token on the bus for one circle, and starting from the second circle of token transmission, the bus enters a normal working stage, and at the moment, a message is sent according to a priority control mechanism. When the workstation receives the token, the workstation initializes THT, then judges whether the THT is less than 0, if the THT is less than 0, directly initializes TRT1, TRT2 and TRT3 and then passes the token. If THT is greater than 0, judging whether a message with the priority of 0 exists, if yes, sending the message with the priority, and judging whether THT is overtime after sending a frame of message, if overtime, still initializing TRT1, TRT2 and TRT 3. If not, the smaller value of the TRT1 and the THT is given to the THT, and the TRT1 is initialized, if the THT after the assignment is greater than 0, a message with the priority of 1 is sent, similarly, whether the THT is overtime is checked after one frame is sent, and if the THT is overtime, the TRT2 is initialized, and the TRT3 is initialized. If there is no message with priority 1, the smaller of the two values TRT2 and THT is given to THT. Similar to the message transmission control mechanism of priority 1, the messages with priority 2 and priority 3 are controlled by TRT2 and TRT3, respectively. If the THT is not overtime after all the messages are sent and the RAT is overtime, resetting the RAT and starting the ring admission function. The station will gradually increase from the station whose physical address is one plus one and traverse backward its successor station, if the successor station is found, its physical address is stored in the successor station register. And if the RAT is overtime under the condition that the message of the local station is not sent and the THT is overtime, not resetting the RAT.

If a fault station appears in the logic ring, the front station of the fault station sends a token twice to visit the fault station, and the visit fails, and the front station of the fault station sequentially traverses the subsequent work stations from the fault station to the back. If the new successor station is the station on the original logic ring, the successor station does not need to go backwards to continue traversing; otherwise, the successor also needs to continue to search for successors according to the mode that addresses are gradually increased.

The method for simulating the linear token data bus based on the OPNET software comprises the following steps:

step 1, defining the format of a data frame;

in step 1, the data frame involved in the linear token data bus protocol includes three frame structures of an application token frame, a token frame and a message frame. These three frame structures require that the type of fields contained in each frame and the number of bits occupied by each field be first set by the packet format editor. Each of the above frames includes SD (Start Delimiter) and ed (end Delimiter), which occupy 4 bits, respectively. The Token Frame further includes a DA (Destination address) field and a TFCS (Token Frame Check) field, each occupying 8 bits. The application token Frame includes 8 bits of FC (Frame control) field and 8 bits of sa (source addresses) field in addition to SD and ED. The application token frame also contains a padding field because the application token frame is variable in length. Since the length of the application token frame cannot be directly determined and varies according to the physical address of the workstation, the padding field is not defined in the packet format and can be appended when the application token needs to be sent. The message frame contains a data message and a station management code, and these two types of messages can be defined by one frame format, and the corresponding value of the FC field is set when actually transmitting. The FC field may be further subdivided into three fields, an FT (Frame Type) field, a Px (Priority) field, and an SMC (Station Management Code) field. The different FT fields represent which type of frame the frame belongs to, e.g., binary 000 for token frame and binary 001 for application token frame. The Px field is from 00 to 11 in binary, i.e., 0 to 3 in decimal, and the priority 0 is the highest priority, and is decremented one by one. Different SMCs represent different station management commands and perform different station management functions. The data frame also includes 8 bits for the FC field, 8 bits for the SA field, 16 bits for the DA field, and 16 bits for the wc (word count) word count field, in addition to the SD and ED fields. The INFO field is specific to the particular message being sent and therefore is not embodied in the packet format editor. A field MFCS (Message Frame Check Sequence) in the Message Frame is used to Check the correctness of the Message Frame, and occupies 16 bits.

Step 2, establishing a core flow of a protocol in a process model;

in the present invention, the various phases of the bus serving the avionics system are described using various states, as shown in fig. 3-8, which are described with sufficient consideration for the reusability of the various states, all of which are described by the following 8 sub-steps.

Step 201, initializing using non-mandatory state description;

in step 201, the initialized variables are shown in Table 4, the variables are described in a language using non-mandatory states, and the initial variables are

TABLE 4 initialization State variables

Name of variable	Means of
		Suc_is_set	Whether or not the successor station address is determined
Frame_addr	Value of the token frame DA field
		Tkn_reptimes	Number of times token is sent to same workstation
BAT	Bus activity timer
		TPT	Token passing timer
BIT	Time to perform built-in self-test
		THT	Token holding timer
TRTx	Token rotation timer
		RAT	Admission ring timer

The model parameter physical address of the node layer is needed to be read during initialization, and the physical address is set at the node layer, not the process layer, so that the physical address is convenient to modify during later research. The obtaining method is to use an own function of the OPNET to obtain the ID of the model firstly, and then to search the father node of the ID model, thereby obtaining the physical address set from the outer layer. And reading the physical address of the node and storing the physical address into a local variable. The process of initialization is an unstationable process, using a mandatory state representation.

Step 202, setting a queue and a queuing and dequeuing mode;

enqueue dequeue queuing of the queue is performed at the message priority in step 202. Because all messages contain 4 types of priorities, 0, 1, 2 and 3 respectively from high to low, the sub-queue is initialized in the process interface, corresponding to 4 queues, MP₀、MP₁、MP₂、MP₃The queue length can be set according to the research requirement, and can be set to be infinite in the ideal condition of research. Writing an enqueue Function in an FB (Function Block) area, analyzing data packaged from an application layer by the enqueue Function, extracting priority information in a field, and then inserting the priority information into a corresponding queue from the tail of the queue according to the priority.

Step 203, setting the functions of self-test and BAT reset;

in step 203, self-test setting and BAT resetting are states leading from an initialization state to a transition line to execute BIT self-test, and self-test time can be set. Setting an interrupt in the self-test state indicates the end of BIT execution. When the execution of BIT is finished, BAT is reset, the method for resetting BAT is also realized by setting interrupt, the types of the two interrupts are self-interrupts, the interrupts are distinguished by marking code numbers of different interrupts, and the states realized by the two functions are non-mandatory states.

Step 204, sending an application token frame;

in the present invention, the process of sending the application token frame is that, since the frame format specification of the application token frame has been completed in step 201, the value is only required to be filled according to each field when sending, and in addition, the length of the variable field of the application token frame is calculated according to the length formula of the application token frame changing along with the physical address, and the variable field is filled according to 4884 codes and sent to the bus through the bus transmitter. The values of the fields are set according to the protocol standard, FC is set to 128, and SA is the physical address of the station. If the application token frame is received before the BAT of the local station is timed out, the interruption of the BAT is cancelled and the non-mandatory state of the static waiting is entered. And the station with BAT overtime can send out the application token frame, if no conflict occurs on the bus in the process of sending, the station can obtain the right of initializing the logic ring and start to send the token frame. The station entering the dormant wait state needs to parse the received frame. If the analysis result shows that the frame is a token frame, whether the DA field of the token frame is the same as the physical address of the workstation is judged, if so, the token is received, the workstation generates a new token, sets TPT and sends the token. And if the received token frame is not the token frame or the received token is not the token for accessing the local station, continuing to enter a waiting static state. However, if the station that has timed out the BAT sends out an application token frame collision, the station that detects the collision needs to reset the BAT again. The above-described judgment and execution functions are described by a mandatory state, the judgment condition is used as a 'conditional instruction' on the transition line, and the executed statement needs to be written on an 'execution instruction' parameter of the state transition line or an entry code area of the mandatory state according to the execution condition.

Step 205, waiting for the response of the subsequent station;

in the present invention, whether the station that initializes the logical ring sends a token or the station that receives the token to access the station sends a new token, it is finally required to enter a state of waiting for a response from a subsequent station. If the TPT timeout interruption occurs in a state of waiting for the response of the subsequent station, the same token is sent again, if the TPT timeout interruption occurs again, the DA field of the token is updated (the DA field is increased by one), and the token is continuously sent. The same token may be allowed to be sent twice, skipping the physical address if no successor station response has been received in both attempts, and continuing the backward progression one by one in accordance with the DA field. If the token frame is received before the TPT is overtime, firstly judging whether the frame is a token frame sent by the station, if so, ignoring the frame, returning to the original state, namely, waiting for the response state of a subsequent station, if not, judging whether the physical address of the token is the same as the physical address of the station, and if the same proves that only two workstations exist on a logical ring, starting the second round of message sending process; if not, entering into static state. When the token frame sent by the non-local station is received, the subsequent station address is indicated to start sending the token, and the subsequent station address needs to be recorded. The two situations are transferred to two different states by two bar state transfer line connection, the message sending state (forced state) is entered after the token accessing the work station is received, the state is transferred to the static state (non-forced state) when the token pointing to other work stations is received and the token is not sent by the work station, and the state is analyzed and judged whether the token accessing the work station is the token accessing the work station or not when the token pointing to other work stations is received and the token is not sent by the work station, if the token is not received, the message sending state is entered, and if the token is not received, the message sending state is returned to the static state.

Step 206, establishing a state transition diagram of the message sending process;

the station that entered the quiescent state in step 204 also enters a messaging state upon receiving a token addressed to the station. When receiving the token pointing to the local station, the THT needs to be initialized, namely, the word interrupt is set at the THT overtime. Firstly, the queue MP with the number of 0 is judged₀If the queue is empty, if not, the queue MP is sent₀Of messages in, only sending queue MP at a time₀A data message of the header. The sending process needs to detect two flags, one of which is a signal of the end of the frame sending, which is provided by the bus transmitter to the MAC layer, and the other is an interrupt of the THT timeout, which is generated by the process itself of the MAC layer. When the THT interruption arrives, three timers of TRT1, TRT2 and TRT3 need to be reset and tokens are transmitted, and the resetting method is to reset the timersThe timer timeout time is reset. When receiving the frame transmission end mark, continuously judging the queue MP₀If it is empty, continue sending queue MP without THT timeout₀The frontmost data message. When queue MP₀When all the messages in the TRT are sent and the THT is not timed out, the TRT1 is initialized, the THT and the TRT1 are refreshed according to the protocol, and whether the event handle of the THT still exists needs to be judged immediately after the THT is refreshed. Because if the TRT1 has timed out before refreshing the THT, the handle to the THT will no longer be present, and subsequent simulations will experience errors. If a handle exists, enter queue MP with priority 1₁The transmission control state of (1). The control mechanism and priority is queue MP₀The message sending control mechanism is similar, firstly judging the queue MP₁And if the time is not empty, sending a message from the head of the queue, and judging whether the THT timer is overtime or not every time one message is sent. The steps for subsequent queues of priority 2 and 3 are the same. The state transition diagram of the whole message transmission should contain 4 non-mandatory states, which respectively represent the state waiting for the end of transmission after the message of the priority is transmitted, and the rest states should be all mandatory states. The effect of the transition graph embodied on the OPNET software platform is highly similar to the messaging mechanism flow diagrams of fig. 3-8.

Step 207, the RAT timer controls the loop;

the setting of the RAT timer is when queue MP₃If all the messages in the system are sent and the THT timer is not overtime, judging whether the RAT is overtime or not, judging whether a time handle of the RAT exists or not by a judging method in software, if so, representing that the time handle is not overtime, carrying out subsequent operation, and transmitting a token to a subsequent station; if not, it represents a timeout, at which point the operation of admitting a ring will be initiated. The method is to modify the originally determined address of the subsequent station into the physical address of the station plus one, send the token and set the TPT, and after the two times of sending failures, the address of the subsequent station plus one continues in sequence. Until a subsequent workstation responds to the token sent by the station, the address of the subsequent station is refreshed to the address of the responding workstation. Functional premises for enabling admission into the ring after a RAT timeoutOne criterion for low message load on the bus is that the workstation can send out a pile of 4 queues (MP) without the THT having timed out₀、MP₁、MP₂、MP₃) All of the messages in (1).

Step 208, fault ring-out;

when a station on the bus fails, it may happen that the station sends a token twice without receiving a response. At this time, a new non-mandatory state of token loss is added, in this state, token transmission is performed twice to the same workstation, and if no response is received, that is, the situation that a new successor station sends a new token is not received, the workstations with normal functions are searched backwards by gradually increasing the physical addresses of the failed stations one by one. The process of finding a new successor requires the use of a flag bit to determine the number of transmissions to the same station. And when the successor station is found, updating the value of the successor station register variable to be the new successor station physical address. If the new successor station is the station in the initial logical ring, the new successor station does not need to continuously search for the successor station, otherwise, the new successor station traverses backwards to search for the successor station according to the mode of initializing the logical ring.

In the present invention, the above non-mandatory state requires a connection to a state transition line pointing to itself, indicating that when an application layer packet arrives, the packet should be enqueued according to priority. In addition, in order to ensure that each non-mandatory state does not have abnormal conditions, a bar state transfer line is connected again, and the condition is default.

The functions involved in step 2 and their functions are shown in the following table, all defined in the FB area in the process editor.

TABLE 5 custom function name and function

Step 3, simulating the state conversion of the application layer;

the purpose of the application layer is to generate data packets at a certain rate, and the application layer enters a standby non-mandatory state from an initialized mandatory state according to the format of a data frame set in a packet format editor. And setting an interrupt in the waiting state, wherein the specific time for the interrupt to occur can be set according to research requirements. If it is desired to start sending the message as early as possible, the interrupt occurrence time is set as close as possible to the simulation time. And entering a message sending stage after the interruption occurs, continuously sending the message by using a state conversion line pointing to the message, generating the interruption at regular intervals, sending the message, executing state conversion once, returning to the message state and refreshing the interruption time, and sending the message again when the next interruption time comes.

Step 4, simulating the architecture of a node layer;

the simulation node layer is formed by a common process, a queue process, a transmitter and a receiver. And (3) binding the process model formed in the step (3) into a common process, and binding the newcastle model formed in the step (2) into a queue process. And then the node model as shown in figure 1 is formed. The connection relationship between the process and the transmitter is shown in table 5:

TABLE 6 connection types of nodes

Step 5, simulating the link characteristics of the bus;

and constructing a link model according to a protocol of the linear token data bus, and selecting a bus type from the supported link types. "close model", "coll model", "ecc model", "error model", "propdel model", "txdel _ model" among the parameters all select default parameter values for the bus, respectively, "dbu _ close", "dbu _ coll", "dbu _ ecc", "dbu _ error", "dbu _ propdel", and "dbu _ txdel", the data rate is set to 50Mbps, and the remaining parameters use default values. These english words come from the OPNET software functional standard without chinese comments.

Step 6, completing the integral construction of the bus under the engineering editor;

and selecting a bus under the topology option and setting a node and link model, namely establishing the whole bus topology structure, wherein the number of workstations of the bus is required to be set in a range of 0 to 127 (including 0 and 127) according to the protocol. After the bus topology is established, a function of controlling bus Failure and Recovery is required to be added, and Failure Recovery under the 'utilities' packet is selected to control the Failure or Recovery of a node or a link at a certain time.

After the simulation platform is established through the 6 steps, simulation can be started. The parameter set in the simulation is very flexible and a set of parameters is given below as a reference.

TABLE 7 parameter settings of workstations

Name (R)	Parameter(s)	Reference value/constraint
			Number of work stations	5	0-127
Physical address of each workstation	0，2，4，5，9	0-127
			Faulty object	Work station 2	Workstation in a logical ring
Time of failure	0.0002s	/
			Recovery time	0.00025s	/
Application layer start packet sending time Tstart	0.00012s	/
			Application layer packet sending interval time Tgap	0.00002s	/
BAT	0.000015*(PA+1)s	0-0.002047s
			TPT	0.00001s	0-0.0000102s
THT	0.0001s	0-0.065535s
			TRT1	0.00020s	0-0.065535s
TRT2	0.00018s	0-0.065535s
			TRT3	0.00016s	0-0.065535s
RAT	0.00016s	0-6.5535s

The ranges referred to in table 7 all contain boundaries. In the present invention, English from OPNET software is a direct reference and is not translated in Chinese.

Claims

1. An OPNET-based linear token data bus simulation platform at least comprises a computer; the simulation platform is characterized in that a common process collection unit (10) is arranged in an application layer, a queue process collection unit (20) is arranged in an MAC layer, and a bus transmission unit (30) and a bus receiving unit (40) are arranged in a physical layer;

the common process collecting unit (10) is used for collecting the data message packet generated by the application layer according to a certain rate and then collecting the data message packet FL₁₀To a queue process collection unit (20) in the MAC layer;

queue process collection unit (20) for receiving data message packets FL₁₀Second aspect is the FL₁₀Stored in message queues according to priorityThe token control unit (20A) of the third aspect performs message transmission according to the state transition rule, and the token control unit of the fourth aspect receives the received data flow FL output by the bus receiving unit (40)_inAnd conflict detection instruction MD₄₀Fifth aspect, the reception bus transmission unit (30) outputs an end-of-frame transmission flag BS₃₀Sixth aspect is to transmit a data stream FL₂₀To a bus transmission unit (30);

the initial state of the application layer for sending the data packet is a Sinit state, the software enters a Swait state from an Init state when being started, and enters a Send state when receiving the information for starting to send the data packet, the data packet is continuously sent to the MAC layer in the Send state,

the method is characterized in that:

successfully applying for the state transition from the token to the waiting token;

when software starts an instruction F, the state of the software enters a BIT state from an Init state, the process of bus self-test execution is simulated by delaying for a period of time, then an application token frame is sent and the state of Jdg _ cll is entered after the BIT execution is finished, and when a bus conflict instruction C occurs, the state of Clm _ tkn is entered and the application token frame is sent again; when the bus has no conflict, the state is directly converted into Tkn _ gt state, and a token frame is sent; if the station entering Clm _ tkn state has no conflict on the bus after sending the application token frame, the station obtains the token sending right when the BAT timer is overtime, and enters Tkn _ gt state; after the token is sent, entering a Wt _ tkn state;

the timer overtime condition instruction A comprises a BAT overtime condition instruction A1, a THT overtime condition instruction A2, a TPT overtime condition instruction A3, a RAT overtime condition instruction A4 and a TRT overtime condition instruction A5;

unsuccessfully applying for a state transition from token to waiting token;

for the station which does not obtain the bus control right in the process of bus contention, namely the station which does not successfully send out the application token frame in the application token phase, after receiving the signal on the bus, the state of the station receives the message condition instruction B from the state Clm _ tkn to enter Analyze, and the frame type and the DA field address are analyzed; if a token frame conditional instruction B11 directed to the station is received, send the token and enter the Wt _ tkn state; entering Wft _ pu state if the application token frame conditional instruction B2 or the message frame conditional instruction B3 or the token frame is not a token frame conditional instruction B12 directed to the station is received;

the received data packet condition command B comprises a received token frame condition command B1, a received application token frame condition command B2 and a received message frame condition command B3; for the token frame conditional instruction B1 received further includes receiving a token frame conditional instruction B11 directed to the station, receiving a token frame conditional instruction B12 not directed to the station; b12 further includes token frame condition instruction B121 sent by the station, and token frame condition instruction B122 not sent by the station;

the token waiting state enters the state conversion of continuously waiting or sending messages according to the received frame information;

entering a Wt _ tkn state, and after the token is sent, starting timing by a TPT timer; if a message condition instruction B is received in a Wt _ tkn state, entering an Analyze state, firstly analyzing whether a received frame is a token frame, if the condition instruction is B1, entering a Jdg _ pkt _ slf state, judging whether the received frame is the token frame sent by a station in the state, if so, returning to the Wt _ tkn state if the received frame is the token frame which is sent by the station, if not, further judging whether a destination address of the token frame is the physical address of the station, if so, receiving the condition instruction B11, indicating that the frame addressed to the station is received, recording a subsequent station address, entering Rcrd _ suc _ addr, judging whether a message queue is empty, if so, receiving a condition instruction D1, sending the token and entering an Wff _ nm state, and if not, entering a Pass _ g state if not, receiving a condition instruction D2; and further judging that the token frame is a token frame, but the destination address field is not the physical address of the station, namely the conditional instruction B122 is received, and the station enters a Pwrup _ idle state after the address of the subsequent station is recorded;

the issue queue information conditional instruction D includes an issue queue empty conditional instruction D1, including an issue queue not empty conditional instruction D2;

the state conversion from the logic ring not established to the logic ring established process;

entering an Analyze state after receiving the message condition instruction B in a Pwrue _ idle state, judging whether the message frame is a token frame or not in the state, entering a Jdg _ addr state if receiving the condition instruction B1, and returning to the Pwrue _ idle state if receiving B2 or B3; judging whether the token address is the physical address of the station under the Jdg _ addr state, if so, receiving a conditional instruction B11, judging whether a message queue is empty, and if not, further receiving a conditional instruction D2, and entering a Pass _ msg state; enter Wff _ nm state if conditional instruction D1 is further received; the process of entering a Pass _ msg state from a Pwrup _ idle state, receiving a message sending ending instruction E after sending a frame of message, judging whether the THT timer is overtime, returning to the self state if the THT timer is not overtime, continuously sending the message, and entering a Wff _ nm state if the THT timer is overtime, namely a conditional instruction A2 is received or a message sending queue is empty, namely a conditional instruction D1 is received;

after the logic ring is established, the state of the message is switched;

the station entering Wff _ nm state, after receiving the message condition instruction B, enters the Analyze state, determines which type of packet it belongs to, if it is a token frame, it will receive the condition instruction B1, enter the Jdg _ pkt _ slf state, if it is not, that is, it receives the condition instruction B2 or B3, it returns to Wff _ nm state, if it is a token directed to itself under the Jdg _ pkt _ slf state, it receives the condition instruction B11, it enters the Cancel _ TPT state, and it determines whether it enters the message sending state according to receiving the condition instruction D1 or the condition instruction D2, after entering the message sending, it returns to the Wff _ nm state.