CN109962858B

CN109962858B - CAN bus data transmission method and control system

Info

Publication number: CN109962858B
Application number: CN201711424469.8A
Authority: CN
Inventors: 胡钱洋; 苏常军; 杨学青; 刘振楠; 王辉; 吴光耀
Original assignee: Yutong Bus Co Ltd
Current assignee: Yutong Bus Co Ltd
Priority date: 2017-12-25
Filing date: 2017-12-25
Publication date: 2023-03-31
Anticipated expiration: 2037-12-25
Also published as: CN109962858A

Abstract

The invention relates to a CAN bus data transmission method and a control system, which are characterized in that when CAN bus data are transmitted, CAN message data are stored in a secondary cache queue, and then the CAN message data are transmitted to a CAN bus from the secondary cache queue according to a set sending period and a set sequence. The method unifies different transmission moments, and no matter what the transmission moment of the traditional CAN message data transmitted to the CAN bus is, the CAN message data is firstly stored in the second-level cache queue and then transmitted to the CAN bus according to a corresponding principle, so that the sending moment of the CAN message data output to the CAN bus is unified, the idle and busy of the CAN bus are avoided, the blockage and delay of the CAN bus and the idle of the CAN bus are further avoided, and the transmission efficiency, the utilization rate and the reliability of the CAN bus are improved.

Description

CAN bus data transmission method and control system

Technical Field

The invention relates to a CAN bus data transmission method and a control system.

Background

The maximum transmission rate of the CAN bus CAN reach 1Mbit/s, at present, two CAN buses are needed to be adopted in a network connection mode on an automobile, one high-speed CAN bus is used for driving a system, and the rate reaches 500kbit/s; the other low-speed CAN bus used for the vehicle body system has the speed of 100-250kbit/s generally. The high-speed CAN bus is mainly connected with systems with high requirements on communication real-time performance, such as an engine, an automatic transmission, ABS/ASR, ESP and the like. The low-speed CAN bus is mainly connected with lamplight, electric vehicle windows, an automatic air conditioner, an information display system and the like, is mostly a low-speed motor and a switching value device, and has low real-time requirement and a large number of devices. CAN networks with different speeds are connected through a gateway. With the increasing maturity and wide application of artificial intelligence technology, higher requirements are put forward on a vehicle-mounted network. Linux systems are also increasingly widely used in vehicle-mounted systems.

Along with the improvement of the automobile intelligent degree, a large number of sensing system devices need to be accessed, meanwhile, the terminal loads on the CAN bus are more and more, on the premise of keeping the number of the original CAN channels, the increase of the CAN terminal loads inevitably brings great pressure to the CAN communication network, and thus, the requirements on the real-time performance and the reliability of the CAN bus under the embedded system are continuously improved. In the CAN system, there are two main real-time influencing factors of the system: network latency and bus communication rate. Therefore, both factors must be considered together. The reliability of CAN communication is mainly prevented from being blocked by a CAN network. The conventional CAN data transmission method is only to transmit data to the CAN bus directly, because the CAN bus has different operating conditions at different times, sometimes idle, sometimes busy jam, that is to say, when a lot of data are transmitted to the CAN bus at the same time just, CAN cause the CAN bus busy, and then CAN lead to the CAN bus to block, reduce transmission efficiency and reliability, when there is no data transmission to the CAN bus just in a period of time, CAN cause the CAN bus idle, reduce the utilization ratio of the CAN bus, correspondingly, its transmission efficiency also reduces. Then, when data transmission is performed by adopting a conventional transmission mode, if data is directly output to the CAN bus without any processing, the CAN bus sometimes has idle data transmission and low transmission efficiency, and sometimes has busy data transmission, which is easy to cause blockage.

Disclosure of Invention

The invention aims to provide a CAN bus data transmission method, which is used for solving the problem that the CAN bus is free and busy sometimes caused by the existing CAN data transmission method. The invention also provides a CAN bus data transmission control system.

In order to achieve the above object, the present invention includes the following technical solutions.

The first method scheme is as follows: the CAN message data are stored in a set secondary cache queue in real time, and the CAN message data in the secondary cache queue are output and sent to a CAN bus according to a set sending period and a set sequence.

When CAN bus data transmission is carried out, CAN message data are stored in a secondary cache queue, and then the CAN message data are transmitted to the CAN bus from the secondary cache queue according to a set sending period and a set sequence. A second-level buffer queue is added to unify different transmission moments, and the CAN message data are stored in the second-level buffer queue firstly no matter what the transmission moments of the CAN message data transmitted to a CAN bus are, and then are transmitted to the CAN bus according to a corresponding principle, so that the transmission moments of the CAN message data output to the CAN bus are unified, namely, under a normal condition, for example, under the condition that the average load of the bus is not overloaded, the CAN message is transmitted to have the functions of peak clipping and valley filling, the idle and busy of the CAN bus are avoided, the instantaneous load of the bus is avoided being too small or too large, the blockage and delay of the CAN bus and the idle of the CAN bus are avoided, and the transmission efficiency, the utilization rate and the reliability of the CAN bus are improved.

The second method scheme comprises the following steps: on the basis of the first method scheme, the data transmission method runs under a Linux system, a CAN data processing thread is added under the Linux system, and the CAN data processing thread outputs and sends CAN message data in the secondary cache queue to a CAN bus according to a set sending cycle and a set sequence.

The third method scheme comprises the following steps: on the basis of the first or second method scheme, the setting sequence is based on a first-in first-out principle, and the CAN message data are sequentially output to the CAN bus from the second-level cache queue according to the first-in first-out principle.

The method scheme is as follows: on the basis of the first method scheme or the second method scheme, the bus data transmission method further implements the following load rate control process: and detecting the actual load rate condition of the CAN bus in real time, comparing the actual load rate with a set load rate threshold, and controlling and increasing the sending period of the CAN message data stored in the secondary cache queue when the actual load rate is greater than the set load rate threshold so as to adjust the actual load rate to be below the set load rate threshold.

The CAN message data is stored in the sending period of the second-level cache queue, namely the storage period is closely related to the load rate of the CAN bus, therefore, when the actual load rate is greater than the set load rate threshold value, the sending period of the CAN message data stored in the second-level cache queue is increased by controlling, the bus load rate is automatically and dynamically adjusted to match the target load rate, the normal and reliable operation of the CAN bus is ensured, the influence of high load rate on the data transmission of the CAN bus is prevented, and the probability of data delay and even frame loss caused by overhigh bus load rate is reduced. Moreover, the current CAN network analysis tools such as CANOE are used to analyze the bus load rate, and then the CAN message sending period is statically set by the control program under the Linux system to match the target load rate, if the peripheral CAN terminal is added, the CAN message sending period needs to be readjusted, and the bus load rate is monitored by the CANOE tool to match the target load rate, so as to prevent the bus from blocking and frame dropping.

The method scheme five: on the basis of the fourth method scheme, when the sending period of the CAN message data stored in the second-level cache queue is adjusted to the maximum value allowed, the actual load rate cannot be smaller than or equal to the set load rate threshold value, and then a corresponding alarm signal is output.

The method comprises the following steps: on the basis of the fourth method scheme, the load rate control process runs under a Linux system, a CAN message monitoring thread is added under the Linux system, and the CAN message monitoring thread realizes the load rate control process.

The first scheme of the system is as follows: the scheme provides a CAN bus data transmission control system, which comprises a CAN bus data transmission control module, wherein the control module comprises a memory, a processor and a computer program which is stored in the memory and CAN run on the processor, and the processor executes the program to realize the following control processes: and storing the CAN message data in a set second-level cache queue in real time, and outputting and sending the CAN message data in the second-level cache queue to a CAN bus according to a set sending period and a set sequence.

And a second system scheme: on the basis of the first system scheme, the data transmission method operates under a Linux system, a CAN data processing thread is added under the Linux system, and the CAN data processing thread outputs and sends CAN message data in the secondary cache queue to a CAN bus according to a set sending period and a set sequence.

And a third system scheme: on the basis of the first or second system scheme, the set sequence is based on a first-in first-out principle, and the CAN message data are sequentially output to the CAN bus from the second-level cache queue according to the first-in first-out principle.

The system scheme is as follows: on the basis of the first system scheme or the second system scheme, the processor executes the program to realize the following load rate control process: and detecting the actual load rate condition of the CAN bus in real time, comparing the actual load rate with a set load rate threshold, and controlling and increasing the sending period of the CAN message data stored in the secondary cache queue when the actual load rate is greater than the set load rate threshold so as to adjust the actual load rate to be below the set load rate threshold.

And a fifth system scheme: on the basis of the fourth system scheme, when the sending period of the CAN message data stored in the second-level cache queue is adjusted to the maximum value allowed, the actual load rate cannot be smaller than or equal to the set load rate threshold value, and then a corresponding alarm signal is output.

And a sixth system scheme: on the basis of the system scheme IV, the load rate control process runs under a Linux system, a CAN message monitoring thread is added under the Linux system, and the CAN message monitoring thread realizes the load rate control process.

Drawings

FIG. 1 is a block diagram of an intelligent controller CAN bus access architecture;

FIG. 2 is a flow diagram of CAN bus supervisory thread one-shot logic;

fig. 3 is a CAN bus monitor thread loop logic flow diagram.

Detailed Description

The invention provides a CAN bus data transmission method, which comprises the following basic processes: and storing the CAN message data in a set second-level cache queue in real time, and outputting and sending the CAN message data in the second-level cache queue to a CAN bus according to a set sending period and a set sequence.

Based on the above basic technical solution, the present invention will be further described in detail with reference to the accompanying drawings.

In this embodiment, the above-mentioned CAN bus data transmission method is applied to an intelligent controller of an unmanned vehicle, the intelligent controller runs a Linux embedded system, and a simple structure diagram of a CAN bus access terminal thereof is shown in fig. 1.

The sending control of CAN message data is added under a Linux system, namely the CAN bus data transmission method provided by the invention. The intelligent controller is loaded with a main control program PA, and the running period of the main control program PA is Tm. In this embodiment, the main control program PA is loaded on the application control program side in the intelligent controller Linux system. The main control program PA is a software program corresponding to the CAN bus data transmission method provided by the present invention. And specially setting a second-level buffer queue, for example, adding the second-level buffer queue to the transmission end processing of the CAN message. A main control program PA in the intelligent controller continuously acquires data from external equipment such as radar and GPS (global positioning system) peripherals through a CAN (controller area network) channel within the running period Tm of a main program, simultaneously performs corresponding operation analysis, and then packs an analysis result or a decision command into CAN message data to be transmitted to the whole vehicle controller in real time. When data is transmitted, the packed CAN message data is stored in the second-level cache queue according to a corresponding sending period, wherein the sending period is the sending period (also called the storage period) for storing the CAN message data in the second-level cache queue. The main control program PA operates one cycle to store the primary CAN message data in the secondary cache queue correspondingly, or the main control program PA operates a plurality of cycles to store the primary CAN message data in the secondary cache queue correspondingly, therefore, the sending cycle of the CAN message data stored in the secondary cache queue may be the operating cycle Tm of the main control program PA, or an integral multiple of the operating cycle Tm of the main control program PA. Under a Linux system, a CAN data processing Thread Thread1 is developed by using a Linux control program, the CAN data processing Thread Thread1 automatically reads CAN message data from a secondary cache queue, and outputs and sends the CAN message data in the secondary cache queue to a CAN bus according to a set sending period and a set sequence, namely, the data in the secondary cache queue is automatically and uniformly taken out and sent to the CAN bus. The set sending period is set according to actual requirements, the set sequence is based on a first-in first-out principle, and CAN message data entering the second-level cache queue first is sent to a CAN bus. Of course, as other embodiments, the transmission may also be performed according to other sequence principles, such as: data may be sent in order of priority, if available. The speed of data sent to the CAN bus by the application layer CAN be balanced by the storage and sequential sending modes, the condition that the CAN bus is idle or busy is avoided, the blockage and delay of the CAN bus and the idle of the CAN bus are further avoided, the condition that data is delayed or even lost is prevented, and the transmission efficiency, the utilization rate and the reliability of the CAN bus are improved.

Furthermore, during the process of storing the CAN message data in the secondary buffer queue, the load rate of the CAN bus CAN be monitored, and then the current load rate is dynamically adjusted according to the current load rate condition, that is, the storage rate of the corresponding CAN message data stored in the secondary buffer queue (that is, the sending period of the CAN message data stored in the secondary buffer queue) is adjusted to stabilize the bus load rate.

To explain the dynamic adjustment process of the load factor, the calculation process of the load factor is first explained below.

Under the condition that the external equipment is stable, the CAN bus load rate is guaranteed to be stable in a constant range in real time, the current vehicle-mounted CAN bus load rate is generally maintained at about 30%, but with more and more external access terminals of the intelligent vehicle, the processing logic is increasingly complex, the control threshold value of the CAN bus load rate is gradually improved in the test, and even the control threshold is expanded to 60% -70% by Feitian research and development engineers. The load rate is the actual data transfer rate on the bus compared to the theoretical maximum data transfer rate. For example, the CAN bus baud rate is 500Kbit/s, the bus message transmission time interval is 50ms, and the single frame message is the longest data frame (the maximum 128 bits of the extended frame) of 8-byte data, then the number of data frames that CAN be supported and transmitted by 50ms under the condition of full bus load is about 39, and the following calculation formula is referred to in detail:

(500000bit/s)*(50ms)/(128bit)

at this time, if we want to maintain the load rate of the CAN bus at about 40%, the number of CAN messages sent in 50ms is not more than about 15 (39 × 0.4).

In order to facilitate subsequent cycle adjustment, a sending cycle interval in which CAN message data is stored in a secondary buffer queue CAN be preset, then, upper and lower limit values of the sending cycle, namely, a minimum allowable value and a maximum allowable value of the cycle, are set first, and the cycle interval is determined according to the upper and lower limit values. And determining the CAN bus load rate F _ load to be controlled, wherein the F _ load is a set CAN bus load rate threshold value, namely a target CAN bus load rate.

The actual CAN bus load rate is then calculated, one calculation is given as follows: according to relevant parameters such as the baud rate of the CAN bus, the maximum CAN message number Num _ total allowed to be received and transmitted in the running period Tm of the main program is calculated according to the calculation formula provided above, a CAN message monitoring Thread Thread2 is additionally arranged in the application program in the intelligent controller, the triggering period of the CAN message monitoring Thread Thread2 is set to be the same as the running period of the main control program, in the Tm period, the monitoring Thread Thread2 monitors the actual CAN message number Num _ CAN read and transmitted on the CAN bus by the main control program PA in real time, and then the bus load rate F _ t = Num _ CAN/Num _ total is calculated.

When F _ t is greater than F _ load, namely the actual load rate is greater than the set target load rate, the sending period of the CAN message data stored in the secondary cache queue is adjusted to the large end within a preset period interval, namely the sending period is increased. Fig. 2 shows a single adjustment flow chart. Further, CAN classify the CAN message data stored in the second-level buffer queue according to the priority, the monitoring Thread2 needs to compare and adjust once to implement the above control process once, preferentially increase the message sending period of low priority according to the classification of the message priority, and then increase the message sending period of higher priority. Therefore, F _ t can be reduced to below the target F _ load value by increasing the period, eventually satisfying: the actual load rate is less than or equal to the set target load rate.

As shown in fig. 3, in the continuous loop operation of the monitoring Thread2, since there is a maximum limit to the sending period of the CAN message data stored in the secondary buffer queue, when the period is adjusted to the maximum value allowed, if the CAN message data is classified according to the priority level, it is: when the sending periods of the messages classified by all the priorities are adjusted to the maximum value of the preset period interval, the F _ t cannot be guaranteed to fall below the target F _ load value, at the moment, the adjustment is stopped, and the main control program PA is informed to send a warning CAN message to remind that the current bus exceeds the preset load rate, and the number of the bus access terminals needs to be re-planned.

Therefore, the bus load rate is monitored in real time, the bus load rate is dynamically adjusted and optimized on the premise of ensuring the real-time requirement of data, and the probability of data delay and even frame loss caused by overhigh bus load rate is reduced. Moreover, through the control, the load rate of the CAN channel CAN be dynamically controlled within a certain range under the condition that the increase of the CAN peripheral channel or the message volume is less, the universality of program operation CAN be improved, and the maintenance workload CAN be reduced. And when the number of external CAN channels or messages increases to exceed the load of the CAN network, the output warning CAN messages remind that the load of the network becomes huge and exceeds the load capacity of the bus, and the CAN network needs to be re-planned.

The specific embodiments are given above, but the present invention is not limited to the described embodiments. The basic idea of the present invention lies in the above basic scheme, and it is obvious to those skilled in the art that no creative effort is needed to design various modified models, formulas and parameters according to the teaching of the present invention. Variations, modifications, substitutions and changes may be made to the embodiments without departing from the principles and spirit of the invention.

The method CAN be used as a computer program, is stored in a memory in a CAN bus data transmission control module in the CAN bus data transmission control system and CAN be operated on a processor in the CAN bus data transmission control module.

Claims

1. A CAN bus data transmission method is characterized in that CAN message data are stored in a set secondary cache queue in real time according to a set sending period, and the CAN message data in the secondary cache queue are output and sent to a CAN bus according to the set sending period and a set sequence; the bus data transmission method also implements the following load rate control process: detecting the actual load rate condition of the CAN bus in real time, wherein the actual load rate is F _ t = Num _ CAN/Num _ total, the Num _ CAN is the number of actual CAN messages read and sent by a main control program PA on the CAN bus, and the Num _ total is the maximum number of CAN messages allowed to be received and sent in an operation period Tm; comparing the actual load rate with a set load rate threshold, and controlling to increase the sending period when the actual load rate is greater than the set load rate threshold, wherein the sending period is equal to the running period Tm of a main control program PA, and the main control program PA is a software program of a CAN bus data transmission method; when the sending period is increased, the Num _ total is increased, and then the actual load rate is decreased so as to adjust the actual load rate to be lower than the set load rate threshold value.

2. The CAN bus data transmission method according to claim 1, wherein the data transmission method is operated under a Linux system, a CAN data processing thread is added under the Linux system, and the CAN data processing thread outputs CAN message data in the secondary cache queue to a CAN bus according to a set transmission cycle and a set sequence.

3. The CAN bus data transmission method according to claim 1 or 2, wherein the setting order is based on a first-in first-out principle, and the CAN message data are sequentially output from the secondary buffer queue to the CAN bus according to the first-in first-out principle.

4. The CAN bus data transmission method according to claim 1, wherein when a transmission cycle of CAN message data stored in the secondary buffer queue is adjusted to a maximum allowable value, and an actual load rate is not greater than or equal to a set load rate threshold, a corresponding alarm signal is output.

5. The CAN bus data transmission method according to claim 1, wherein the load rate control process is run under a Linux system, a CAN message monitoring thread is added under the Linux system, and the CAN message monitoring thread implements the load rate control process.

6. A CAN bus data transmission control system comprising a CAN bus data transmission control module including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the following control procedures when executing the program: storing the CAN message data in a set secondary cache queue according to a set sending period in real time, and outputting and sending the CAN message data in the secondary cache queue to a CAN bus according to the set sending period and a set sequence;

the processor, when executing the program, also implements the following load rate control process: detecting the actual load rate condition of the CAN bus in real time, wherein the actual load rate is F _ t = Num _ CAN/Num _ total, the Num _ CAN is the number of actual CAN messages read and sent by a main control program PA on the CAN bus, and the Num _ total is the maximum number of CAN messages allowed to be received and sent in an operation period Tm; comparing the actual load rate with a set load rate threshold, and controlling to increase the sending period when the actual load rate is greater than the set load rate threshold, wherein the sending period is equal to the running period Tm of a main control program PA, and the main control program PA is a software program of a CAN bus data transmission method; when the sending period is increased, the Num _ total is increased, and then the actual load rate is decreased so as to adjust the actual load rate to be lower than the set load rate threshold value.

7. The CAN bus data transmission control system according to claim 6, wherein the data transmission method operates under a Linux system, a CAN data processing thread is added under the Linux system, and the CAN data processing thread outputs CAN message data in the secondary cache queue to a CAN bus according to a set transmission cycle and a set sequence.

8. The CAN bus data transmission control system according to claim 6 or 7, wherein the setting order is based on a first-in first-out principle, and the CAN message data are sequentially output from the secondary buffer queue to the CAN bus according to the first-in first-out principle.

9. The CAN bus data transmission control system of claim 6, wherein when the transmission period is adjusted to the maximum value allowed, the actual load rate cannot be made smaller than or equal to the set load rate threshold, and a corresponding alarm signal is output.

10. The CAN bus data transmission control system of claim 6, wherein the load rate control process operates under a Linux system, a CAN message monitoring thread is added under the Linux system, and the CAN message monitoring thread implements the load rate control process.