CN114928427A - Clock synchronization method, device, equipment and storage medium of vehicle-mounted sensor - Google Patents

Abstract

The embodiment of the application belongs to the technical field of digital information transmission, and relates to a clock synchronization method, a clock synchronization device, clock synchronization equipment and a clock synchronization storage medium for a vehicle-mounted sensor. Compared with the existing mainstream centralized bus topological structure, the vehicle-mounted sensor has the advantages that the distributed mesh topological structure is adopted, the flow is dispersed in the independent subnets, the influence of network jitter on clock synchronization based on PTP can be reduced, the influence of network congestion is effectively reduced, meanwhile, the flexibility of network wiring is increased, the deployment space and the freedom degree of the sensor are expanded, and the robustness of the system is improved; in addition, the clock source of the reference clock can be automatically switched according to the signal intensity, so that the sensors can still normally work, and the stability of the device is improved.

Description

Clock synchronization method, device, equipment and storage medium of vehicle-mounted sensor

Technical Field

The present disclosure relates to the field of digital information transmission technologies, and in particular, to a clock synchronization method, apparatus, device, and storage medium for a vehicle-mounted sensor.

Background

Automatic driving is a technology for realizing unmanned driving through a computer system, improves travel efficiency and driving experience, and is an important development direction in the automobile industry at present. Automatic driving relies on the cooperation of artificial intelligence, computer vision, GPS and radar etc. can let the computer take over the car, liberates people from boring driving. The automatic driving technology needs various sensors of the vehicle to work cooperatively, but at present, the vehicle sensors mainly adopt an independent working mode, such as distance and speed measurement by a radar and target detection by a camera. The vehicle does not have the capability of deeply fusing data from different sensors, and the vehicle sensing capability is weak due to insufficient information sharing in the vehicle, so that the vehicle sensing capability becomes a bottleneck limiting the development of the automatic driving technology. In order to realize perception fusion in the automatic driving technology, accurate clock synchronization of data of different sensors is required.

A clock synchronization method is known, as shown in fig. 1, that is, a centralized structure is adopted, all sensors are connected through a switch to form a local area network, and a master clock and a plurality of slave clocks are defined. Messages are periodically transmitted between the master clock and the slave clock, and the slave clock calculates the deviation from the master clock and the network delay by recording the time stamps of transmitting and receiving the PTP messages.

However, the applicant finds that the conventional clock synchronization method is generally not intelligent, the clock synchronization based on the PTP protocol has high requirements on the network environment, and the network jitter affects the clock synchronization accuracy. All messages of the network structure are forwarded through the same switch, network congestion is easy to occur, packet loss or PTP message delay is caused, and clock synchronization precision is affected, so that the problem that the traditional clock synchronization method is low in synchronization precision is seen.

Disclosure of Invention

An object of the embodiments of the present application is to provide a clock synchronization method, apparatus, device and storage medium for a vehicle-mounted sensor, so as to solve the problem of low synchronization accuracy in a conventional clock synchronization method.

In order to solve the above technical problem, an embodiment of the present application provides a clock synchronization method for a vehicle-mounted sensor, which adopts the following technical solutions:

after a time synchronization trigger instruction is received, initializing a reference clock to obtain an initialized reference clock;

acquiring signal intensity information of an external clock in real time;

if the signal intensity information meets a preset signal intensity threshold value, performing first synchronous operation on the initialization reference clock according to the external clock to obtain a first synchronous reference clock;

if the signal intensity does not meet the preset signal intensity threshold value, performing second synchronous operation on the initialization reference clock according to a local clock to obtain a second synchronous reference clock;

and performing the second synchronization operation on the vehicle-mounted sensors according to the first synchronization reference clock or the second synchronization reference clock, wherein the vehicle-mounted sensors perform topological connection according to a mesh topology structure.

In order to solve the above technical problem, an embodiment of the present application further provides a clock synchronization device for a vehicle-mounted sensor, which adopts the following technical solutions:

the initialization module is used for initializing the reference clock after receiving the time synchronization triggering instruction to obtain an initialized reference clock;

the signal acquisition module is used for acquiring signal intensity information of an external clock in real time;

the first reference clock synchronization module is used for carrying out first synchronization operation on the initialization reference clock according to the external clock to obtain a first synchronization reference clock if the signal intensity information meets a preset signal intensity threshold;

the second reference clock synchronization module is used for performing second synchronization operation on the initialization reference clock according to a local clock to obtain a second synchronization reference clock if the signal strength does not meet the preset signal strength threshold;

and the sensor synchronization module is used for performing the second synchronization operation on the vehicle-mounted sensor according to the first synchronization reference clock or the second synchronization reference clock, wherein the vehicle-mounted sensor performs topology connection according to a mesh topology structure.

In order to solve the above technical problem, an embodiment of the present application further provides an apparatus, which adopts the following technical solution:

comprising a memory having computer readable instructions stored therein and a processor which when executed implements the steps of the method for clock synchronization of an onboard sensor as described above.

In order to solve the foregoing technical problem, an embodiment of the present application further provides a storage medium, which adopts the following technical solutions:

the storage medium has stored thereon computer readable instructions which, when executed by a processor, implement the steps of the method for clock synchronization of an in-vehicle sensor as described above.

The application provides a clock synchronization method of a vehicle-mounted sensor, which comprises the following steps: after a time synchronization trigger instruction is received, initializing a reference clock to obtain an initialized reference clock; acquiring signal intensity information of an external clock in real time; if the signal intensity information meets a preset signal intensity threshold value, performing first synchronous operation on the initialization reference clock according to the external clock to obtain a first synchronous reference clock; if the signal intensity does not meet the preset signal intensity threshold value, performing second synchronous operation on the initialization reference clock according to a local clock to obtain a second synchronous reference clock; and performing the second synchronization operation on the vehicle-mounted sensors according to the first synchronization reference clock or the second synchronization reference clock, wherein the vehicle-mounted sensors perform topological connection according to a mesh topology structure. Compared with the prior art, the vehicle-mounted sensor adopts a distributed mesh topology structure, and compared with the current mainstream centralized bus topology structure, the vehicle-mounted sensor disperses the flow in sub-networks which are independent one by one, so that the influence of network jitter on clock synchronization based on PTP (precision time protocol) can be reduced, the influence of network congestion is effectively reduced, meanwhile, the flexibility of network wiring is increased, the deployment space and the degree of freedom of the sensor are expanded, and the robustness of a system is improved; in addition, the clock source of the reference clock can be automatically switched according to the signal intensity, so that the sensors can still normally work, and the stability of the device is improved.

Drawings

In order to more clearly illustrate the solution of the present application, the drawings needed for describing the embodiments of the present application will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present application, and that other drawings can be obtained by those skilled in the art without inventive effort.

Fig. 1 is a schematic diagram of a centralized structure of a conventional clock synchronization method provided in an embodiment of the present application;

FIG. 2 is an exemplary system architecture diagram that may be employed in connection with embodiments of the present application;

FIG. 3 is a flowchart of an implementation of a clock synchronization method for a vehicle-mounted sensor according to an embodiment of the present application;

FIG. 4 is a diagram of a multi-sensor topology according to an embodiment of the present disclosure;

FIG. 5 is a flowchart of an embodiment of a method for synchronizing local clocks according to an embodiment of the present application;

FIG. 6 is a timing interaction diagram of a specific implementation of the PTP clock synchronization principle provided by an embodiment of the present application;

FIG. 7 is a block diagram illustrating an embodiment of a multi-node model of a sensor according to an embodiment of the present disclosure;

FIG. 8 is a block diagram illustrating an exemplary implementation of sensor classification with time accuracy according to an embodiment of the present disclosure;

FIG. 9 is a block diagram illustrating an embodiment of a multi-sensor topology when a node fails according to an embodiment of the present application;

FIG. 10 is a block diagram of one embodiment of a multi-sensor topology provided by an embodiment of the present application when a sensor C10 is added;

fig. 11 is a schematic structural diagram of a clock synchronization apparatus of an in-vehicle sensor according to a second embodiment of the present application;

fig. 12 is a schematic structural diagram of an embodiment of a synchronous local clock apparatus according to a second embodiment of the present application;

FIG. 13 is a schematic block diagram of one embodiment of an apparatus according to the present application.

Detailed Description

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the terms "including" and "having," and any variations thereof, in the description and claims of this application and the description of the above figures are intended to cover non-exclusive inclusions. The terms "first," "second," and the like in the description and claims of this application or in the foregoing drawings are used for distinguishing between different objects and not for describing a particular sequential order.

Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is explicitly and implicitly understood by one skilled in the art that the embodiments described herein can be combined with other embodiments.

In order to make the technical solutions better understood by those skilled in the art, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings.

As shown in fig. 2, the clock sources of the clock synchronization system of the present application include two types: the external clock source uses Beidou or GPS signals, the local clock adopts a real-time clock chip, one of the two clock sources can be selected as a reference clock according to needs, and the reference signal is provided for the whole multi-sensor clock synchronization system. The sensors are connected by adopting a latticed network topology structure, and PTP messages are exchanged based on the Ethernet. The sensors calculate the clock deviation and the path delay between the sensors by recording the timestamps of sending and receiving the PTP messages, calibrate the deviation and realize the clock synchronization between the sensors.

Example one

Continuing to refer to fig. 3, a flowchart of an implementation of a clock synchronization method for an on-board sensor provided in an embodiment of the present application is shown, and for convenience of explanation, only the portion related to the present application is shown.

The clock synchronization method of the vehicle-mounted sensor comprises the following steps:

step S301: and after receiving the time synchronization trigger instruction, initializing the reference clock to obtain an initialized reference clock.

Step S302: and acquiring signal strength information of the external clock in real time.

Step S303: and if the signal intensity information meets the preset signal intensity threshold value, performing first synchronous operation on the initialization reference clock according to the external clock to obtain a first synchronous reference clock.

Step S304: and if the signal intensity does not meet the preset signal intensity threshold value, performing second synchronous operation on the initialization reference clock according to the local clock to obtain a second synchronous reference clock.

Step S305: and performing second synchronization operation on the vehicle-mounted sensors according to the first synchronization reference clock or the second synchronization reference clock, wherein the vehicle-mounted sensors are topologically connected according to the mesh topology structure.

In the embodiment of the application, in the driving process of the automobile, the default use is that the Beidou or the GPS is used as the reference of clock synchronization, but due to the complex road condition, in order to ensure that the automobile drives into the area without the GPS or the Beidou signals, each sensor can work normally temporarily, and a local clock is added to be used as a standby clock source of the vehicle-mounted sensor.

In practical application, under normal conditions, an external clock (Beidou or GPS) is used as a clock source of a reference clock to provide a reference signal for the whole vehicle-mounted sensor clock synchronization network, and at the moment, the local clock also uses the external clock as the reference signal to synchronize the clock of the local clock. When the automobile enters a Beidou or GPS signal weak area, even no signal exists, in order to guarantee normal work between the sensors, the clock source of the reference clock is switched to the local clock by an external clock.

In the embodiment of the present application, referring to fig. 4, the synchronization between multiple sensors in the present application adopts a mesh topology. Each sensor can have a plurality of nodes, and the nodes are in three states: m (master), S (slave) and P (passive). The node is in the M state to provide clock signals for other sensor nodes, the node is in the S state to receive signals provided by other clock nodes, and the node is in the P state to indicate that the node is in an inactivated state. Each clock node can have a plurality of nodes in M or P state, but only one node in S state, and the S and P state can be converted to each other. The solid lines in the figure indicate that the network connection is activated and the dashed lines indicate that the network connection is not activated.

In the embodiment of the present application, each sensor node acquires a clock signal from a previous-stage clock node and provides a clock signal for a next-stage clock. The network is only a network segment connected with a plurality of vehicle-mounted sensors, and the network can be expanded in the up-down direction and the left-right direction, so that the flexibility of network deployment is greatly enhanced.

In an embodiment of the present application, a clock synchronization method for a vehicle-mounted sensor is provided, including: after a time synchronization trigger instruction is received, initializing a reference clock to obtain an initialized reference clock; acquiring signal intensity information of an external clock in real time; if the signal intensity information meets a preset signal intensity threshold, performing first synchronous operation on the initialization reference clock according to an external clock to obtain a first synchronous reference clock; if the signal intensity does not meet the preset signal intensity threshold value, performing second synchronous operation on the initialization reference clock according to the local clock to obtain a second synchronous reference clock; and performing second synchronous operation on the vehicle-mounted sensors according to the first synchronous reference clock or the second synchronous reference clock, wherein the vehicle-mounted sensors are topologically connected according to the mesh topology structure. Compared with the prior art, the vehicle-mounted sensor adopts a distributed mesh topology structure, and compared with the current mainstream centralized bus topology structure, the vehicle-mounted sensor disperses the flow in sub-networks which are independent one by one, so that the influence of network jitter on clock synchronization based on PTP (precision time protocol) can be reduced, the influence of network congestion is effectively reduced, meanwhile, the flexibility of network wiring is increased, the deployment space and the degree of freedom of the sensor are expanded, and the robustness of a system is improved; in addition, the clock source of the reference clock can be automatically switched according to the signal intensity, so that the sensors can still normally work, and the stability of the device is improved.

Continuing to refer to fig. 5, a flowchart of a specific implementation of a method for synchronizing local clocks according to an embodiment of the present application is shown, and for convenience of illustration, only the portions relevant to the present application are shown.

In some optional implementations of this embodiment, after step S303, the method further includes:

step S501: and performing second synchronization operation on the local clock according to the first synchronization reference clock.

In the embodiment of the present application, when the reference clock selects the external clock as the clock source, the reference clock is also the master clock of the local clock at the same time, that is, the local clock also needs to implement clock synchronization to the reference clock.

In some optional implementations of this embodiment, the second synchronization operation is implemented based on a PTP clock synchronization principle.

In the embodiment of the present application, the PTP protocol implements clock synchronization between devices based on ethernet, and the principle of PTP clock synchronization is first introduced here. As shown in fig. 6, two clock nodes are included: the master clock (master clock) and the slave clock (slave clock) take the master clock as a reference, and correct the clock deviation of the slave equipment by calculating the master-slave clock offset and the network delay.

In the embodiment of the present application, the PTP clock synchronization principle is implemented as follows:

firstly, a master clock sends a Sync message to a slave clock, and the sending time t1 is recorded; after receiving the message from the clock, the time of reception t2 is recorded.

Secondly, after the master clock sends the Sync message, a Follow _ Up message carrying t1 is sent.

Sending a Delay _ Req message from the slave clock to the master clock, initiating the calculation of reverse transmission Delay, and recording the sending time t 3; after receiving the message, the master clock records the receiving time t 4.

Fourthly, after receiving the Delay _ Req message, the master clock replies a Delay _ Resp message carrying t 4.

At this time, the four timestamps of t 1-t 4 are obtained from the slave clock, so that the total round-trip delay between the master clock and the slave clock is calculated to be [ (t 2-t 1) + (t 4-t 3) ], and the path delay between the master clock and the slave clock is calculated to be [ (t 2-t 1) + (t 4-t 3) ]/2 because the network is symmetrical. The clock skew of the slave clock relative to the master clock is: offset = (t 2-t 1) - [ (t 2-t 1) + (t 4-t 3) ]/2 = [ (t 2-t 1) - (t 4-t 3) ]/2. Therefore, the slave clock can correct the deviation with the master clock, and the clock synchronization between the master node and the slave node is realized.

In the embodiment of the present application, the above description about the time synchronization principle is the clock synchronization between two nodes, and the nodes are divided into a master clock and a slave clock. It is extended here to achieve clock synchronization between more nodes. The vehicle-mounted sensor can comprise a plurality of nodes, and the nodes can work in a slave clock mode and are synchronous with a clock of a node at the upper stage. Or in a master clock mode, providing a clock reference signal for the next-stage node, and realizing clock synchronization between every two connected nodes based on the principle shown in fig. 6.

In some optional implementations of this embodiment, the vehicle-mounted sensor includes a hardware timestamp type and a software timestamp type, and the vehicle-mounted sensor performs the local topology link according to the hardware timestamp type or the software timestamp type.

In the embodiment of the present application, the sensors of the present application use a mesh topology, and each sensor may be connected to multiple other sensors, so that each sensor needs to support a multi-node mode. As shown in fig. 7, which is a multi-node model of a sensor, each node of the sensor includes a network interface for communicating with other nodes, and PTP messages are transmitted and received through the network interface. The time stamp generator is used for generating time stamps when the PTP messages are sent or received, and the time stamps are divided into two types: the hardware timestamp generator is positioned on a driving layer, so that the recorded time is more accurate, corresponding hardware support is required, and the cost is higher. The software timestamp generator is positioned at an application layer, records software system time, has slightly lower precision, does not need hardware support and has lower cost. One of the two timestamps is selected according to actual requirements, and the distinguishing and the control of the hardware timestamp and the software timestamp are realized.

In the embodiment of the application, the vehicle-mounted sensor can support a plurality of clock nodes, and the nodes are in three states: m (master), S (slave) and P (passive), wherein each clock node is independently and interactively communicated with one clock node of other sensors. Only one node in a plurality of nodes of the same sensor can be in an S state, so that synchronization with the previous-stage clock node is realized, and a local clock is updated. And if the node is in the M state, taking the updated local clock as a reference to serve as a master clock of other sensor time nodes connected with the node.

In the embodiment of the application, because the vehicle-mounted sensors are various in types, the requirements of different sensors on the time precision are different, for example, if the precision needs to reach a sub-microsecond level, the time for accessing the network card when the PTP message between the master node and the slave node is sent or received, that is, the hardware timestamp, must be recorded. And if the precision only needs to reach the millisecond level, the system time of corresponding sensor software, namely the software timestamp, is recorded when the PTP message enters and exits the node, and the millisecond clock synchronization can be realized. Hardware timestamps require hardware support, adding additional cost.

In the embodiments of the present application, the present application uses domain management, and the sensors are classified into two types: hardware timestamp enabled sensors and software timestamp only sensors. The precision of the two sensors is sequentially changed from high to low, and the hardware cost is also changed from high to low. By using domain management, all sensors can be divided into two domains according to actual requirements in the same network topology structure, so that the condition that all sensors require to support hardware timestamps is avoided, and the cost is reduced. Separate control of software timestamps and hardware timestamps is achieved through domain management.

In the embodiment of the application, a field timestamp is customized in the PTP message to distinguish the category of the timestamp. When the sensor accesses the network, whether the sensor needs to support hardware time stamp is identified through the field. As shown in fig. 8, sensors are classified into two categories according to whether hardware time stamping is supported: dark colors indicate support for hardware timestamps and light colors indicate support for software timestamps only. When a certain sensor is accessed to the network, the sensor can automatically negotiate with peripheral sensors, and a proper sensor is selected as a previous-stage node of clock synchronization. If a sensor supporting hardware time stamp accesses the network, but the upper level sensor node does not support the hardware time stamp, the sensor is refused to access. Therefore, all the sensors on the same link can be ensured to be in the same type (high clock precision or low time precision), and the influence of the low-precision sensors on the high-precision sensors is avoided.

In some optional implementations of this embodiment, when one sensor fails, how the clock synchronization network performs adaptive adjustment is performed. Assuming that the initial state of the sensor connection is as shown in fig. 4, when the sensor C5 has a fault, since the sensor C8 uses the sensor C5 as a master clock, when the sensor C8 continuously sends no response to the message sent by the sensor C5 three times and the duration exceeds 5S, the sensor C8 determines that the sensor C5 has a fault, closes the node connected to the sensor C5, sets the node state from S to P, and at the same time, the sensor C8 sends a negotiation message to the peripheral sensors, finally selects the sensor C7 as a new master clock by the BMCA algorithm, and sets the node state connected to the sensor C7 to S, with the result as shown in fig. 9.

In some optional implementation manners of this embodiment, it is assumed that an initial state is shown in fig. 4, when a new sensor C10 needs to be added, the sensor sends a multicast message to a peripheral sensor, it is assumed that there are sensors C7, C8, and C9 that can be selected in the periphery, through a BMCA algorithm, the sensor C8 is finally selected as a master clock, a node state connected to C8 is set to S, and a state connected to sensors C7 and C9 is set to P, and as a result, the result is shown in fig. 10.

The application is operational with numerous general purpose or special purpose computing system environments or configurations. For example: personal computers, server computers, hand-held or portable devices, tablet-type devices, multiprocessor systems, microprocessor-based systems, set top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, distributed computing environments that include any of the above systems or devices, and the like. The application may be described in the general context of computer-executable instructions, such as program modules, being executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. The application may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote computer storage media including memory storage devices.

Those skilled in the art will appreciate that all or part of the processes of the methods of the embodiments described above can be implemented by hardware related to computer readable instructions, which can be stored in a computer readable storage medium, and when executed, the computer readable instructions can include the processes of the embodiments of the methods described above. The storage medium may be a non-volatile storage medium such as a magnetic disk, an optical disk, a Read-Only Memory (ROM), or a Random Access Memory (RAM).

It should be understood that, although the steps in the flowcharts of the figures are shown in order as indicated by the arrows, the steps are not necessarily performed in order as indicated by the arrows. The steps are not performed in the exact order shown and may be performed in other orders unless explicitly stated herein. Moreover, at least a portion of the steps in the flow chart of the figure may include multiple sub-steps or multiple stages, which are not necessarily performed at the same time, but may be performed at different times, and the order of execution is not necessarily sequential, but may be performed alternately or alternately with other steps or at least a portion of the sub-steps or stages of other steps.

Example two

With further reference to fig. 11, as an implementation of the method shown in fig. 3, the present application provides an embodiment of a clock synchronization apparatus for an in-vehicle sensor, where the embodiment of the apparatus corresponds to the embodiment of the method shown in fig. 3, and the apparatus may be applied to various electronic devices.

As shown in fig. 11, the clock synchronization device 100 of the in-vehicle sensor according to the present embodiment includes: the initialization module 110, the signal acquisition module 120, the first reference clock synchronization module 130, the second reference clock synchronization module 140, and the sensor synchronization module 150. Wherein:

the initialization module 110 is configured to perform initialization operation on a reference clock after receiving a time synchronization trigger instruction, so as to obtain an initialized reference clock;

a signal collecting module 120, configured to collect signal strength information of an external clock in real time;

the first reference clock synchronization module 130 is configured to, if the signal strength information meets a preset signal strength threshold, perform a first synchronization operation on the initialization reference clock according to an external clock to obtain a first synchronization reference clock;

the second reference clock synchronization module 140 is configured to, if the signal strength does not meet the preset signal strength threshold, perform a second synchronization operation on the initialization reference clock according to the local clock to obtain a second synchronization reference clock;

and a sensor synchronization module 150, configured to perform a second synchronization operation on the vehicle-mounted sensors according to the first synchronization reference clock or the second synchronization reference clock, where the vehicle-mounted sensors perform topological connection according to the mesh topology structure.

In the embodiment of the application, in the driving process of the automobile, the default use is that the Beidou or the GPS is used as the reference of clock synchronization, but due to the complex road condition, in order to ensure that the automobile drives into the area without the GPS or the Beidou signals, each sensor can work normally temporarily, and a local clock is added to be used as a standby clock source of the vehicle-mounted sensor.

In practical application, under normal conditions, an external clock (Beidou or GPS) is used as a clock source of a reference clock to provide a reference signal for the whole vehicle-mounted sensor clock synchronization network, and at the moment, the local clock also uses the external clock as the reference signal to synchronize the clock of the local clock. When the automobile drives into a Beidou or GPS signal weak area, even no signal exists, at the moment, in order to ensure that the sensors can still work normally, the clock source of the reference clock is switched to the local clock by an external clock.

In the embodiment of the present application, referring to fig. 4, the synchronization between multiple sensors in the present application adopts a mesh topology. Each sensor can have a plurality of nodes, and the nodes are in three states: m (master), S (slave) and P (passive). The node is in the M state to provide clock signals for other sensor nodes, the node is in the S state to receive signals provided by other clock nodes, and the node is in the P state to indicate that the node is in an inactivated state. Each clock node can have a plurality of nodes in M or P state, but only one node in S state, and the S and P state can be converted to each other. The solid lines in the figure indicate that the network connection is activated and the dashed lines indicate that the network connection is not activated.

In the embodiment of the present application, each sensor node acquires a clock signal from a previous-stage clock node and provides a clock signal for a next-stage clock. The network is only a network segment connected with a plurality of vehicle-mounted sensors, and the network can be expanded in the up-down direction and the left-right direction, so that the flexibility of network deployment is greatly enhanced.

In an embodiment of the present application, a clock synchronization apparatus 100 for an in-vehicle sensor is provided, including: the initialization module 110 is configured to perform initialization operation on a reference clock after receiving a time synchronization trigger instruction, so as to obtain an initialized reference clock; the signal acquisition module 120 is used for acquiring signal intensity information of an external clock in real time; the first reference clock synchronization module 130 is configured to, if the signal strength information meets a preset signal strength threshold, perform a first synchronization operation on the initialization reference clock according to an external clock to obtain a first synchronization reference clock; the second reference clock synchronization module 140 is configured to, if the signal strength does not meet the preset signal strength threshold, perform a second synchronization operation on the initialized reference clock according to the local clock to obtain a second synchronized reference clock; and a sensor synchronization module 150, configured to perform a second synchronization operation on the vehicle-mounted sensors according to the first synchronization reference clock or the second synchronization reference clock, where the vehicle-mounted sensors perform topological connection according to the mesh topology structure. Compared with the prior art, the vehicle-mounted sensor adopts a distributed mesh topology structure, and compared with the current mainstream centralized bus topology structure, the vehicle-mounted sensor disperses the flow in sub-networks which are independent one by one, so that the influence of network jitter on clock synchronization based on PTP (precision time protocol) can be reduced, the influence of network congestion is effectively reduced, meanwhile, the flexibility of network wiring is increased, the deployment space and the degree of freedom of the sensor are expanded, and the robustness of a system is improved; in addition, the clock source of the reference clock can be automatically switched according to the signal intensity, so that the sensors can still normally work, and the stability of the device is improved.

Continuing to refer to fig. 12, a schematic structural diagram of a specific implementation of the synchronous local clock apparatus provided in the second embodiment of the present application is shown, and for convenience of description, only the portions related to the present application are shown.

In some optional implementations of the present embodiment, the clock synchronization apparatus 100 of the vehicle-mounted sensor further includes: a local clock synchronization module 160, wherein:

and a local clock synchronization module 160, configured to perform a second synchronization operation on the local clock according to the first synchronization reference clock.

In the embodiment of the present application, when the reference clock selects the external clock as the clock source, the reference clock is also the master clock of the local clock at the same time, that is, the local clock also needs to implement clock synchronization to the reference clock.

In some optional implementations of this embodiment, the second synchronization operation is implemented based on a PTP clock synchronization principle.

In the embodiment of the present application, the PTP protocol implements clock synchronization between devices based on ethernet, and the principle of PTP clock synchronization is first introduced here. As shown in fig. 6, two clock nodes are included: the master clock (master clock) and the slave clock (slave clock) take the master clock as a reference, and correct the clock deviation of the slave equipment by calculating the master-slave clock offset and the network delay.

In the embodiment of the present application, the PTP clock synchronization principle is implemented as follows:

firstly, a master clock sends a Sync message to a slave clock, and the sending time t1 is recorded; after receiving the message from the clock, the time of reception t2 is recorded.

Secondly, after the master clock sends the Sync message, a Follow _ Up message carrying t1 is sent.

Sending a Delay _ Req message from the slave clock to the master clock, initiating the calculation of reverse transmission Delay, and recording the sending time t 3; after receiving the message, the master clock records the receiving time t 4.

Fourthly, after receiving the Delay _ Req message, the master clock replies a Delay _ Resp message carrying t 4.

At this time, the four timestamps of t 1-t 4 are obtained from the slave clock, so that the total round-trip delay between the master clock and the slave clock is calculated to be [ (t 2-t 1) + (t 4-t 3) ], and the path delay between the master clock and the slave clock is calculated to be [ (t 2-t 1) + (t 4-t 3) ]/2 because the network is symmetrical. The clock skew of the slave clock relative to the master clock is: offset = (t 2-t 1) - [ (t 2-t 1) + (t 4-t 3) ]/2 = [ (t 2-t 1) - (t 4-t 3) ]/2. Therefore, the slave clock can correct the deviation with the master clock, and the clock synchronization between the master node and the slave node is realized.

In the embodiment of the present application, the above-mentioned description about the time synchronization principle is the clock synchronization between two nodes, and the nodes are divided into a master clock and a slave clock. Here it is extended to achieve clock synchronization between more nodes. The vehicle-mounted sensor can comprise a plurality of nodes, and the nodes can work in a slave clock mode and are synchronous with the clock of the node at the previous stage. And the clock synchronization module can also work in a master clock mode to provide a clock reference signal for the next-stage node, and the clock synchronization between every two connected nodes is realized based on the principle shown in fig. 6.

In some optional implementation manners of this embodiment, the vehicle-mounted sensor includes a hardware timestamp type and a software timestamp type, and the vehicle-mounted sensor performs the local topology link according to the hardware timestamp type or the software timestamp type.

In the embodiment of the present application, the sensors of the present application use a mesh topology, and each sensor may be connected to multiple other sensors, so that each sensor needs to support a multi-node mode. As shown in fig. 7, which is a multi-node model of a sensor, each node of the sensor includes a network interface for communicating with other nodes, and PTP messages are transmitted and received through the network interface. The time stamp generator is used for generating time stamps when the PTP messages are sent or received, and the time stamps are divided into two types: the hardware timestamp generator is positioned on a driving layer, so that the recorded time is more accurate, corresponding hardware support is required, and the cost is higher. The software timestamp generator is positioned at an application layer, records software system time, has slightly lower precision, does not need hardware support and has lower cost. One of the two timestamps is selected according to actual requirements, and the distinguishing and the control of the hardware timestamp and the software timestamp are realized.

In the embodiment of the application, the vehicle-mounted sensor can support a plurality of clock nodes, and the nodes are in three states: m (master), S (slave) and P (passive), wherein each clock node is independently and interactively communicated with one clock node of other sensors. Only one node in a plurality of nodes of the same sensor can be in an S state, so that synchronization with a previous-stage clock node is realized, and a local clock is updated. And if the node is in the M state, taking the updated local clock as a reference to serve as the master clock of other sensor time nodes connected with the node.

In the embodiment of the application, because the vehicle-mounted sensors are various in types, the requirements of different sensors on the time precision are different, for example, if the precision needs to reach a sub-microsecond level, the time for accessing the network card when the PTP message between the master node and the slave node is sent or received, that is, the hardware timestamp, must be recorded. And if the precision only needs to reach the millisecond level, the system time of corresponding sensor software, namely the software timestamp, is recorded when the PTP message enters and exits the node, and the millisecond clock synchronization can be realized. Hardware timestamps require hardware support, adding additional cost.

In the embodiments of the present application, the present application uses domain management, and the sensors are classified into two types: hardware timestamp enabled sensors and software timestamp only sensors. The precision of the two sensors is sequentially changed from high to low, and the hardware cost is also changed from high to low. By using domain management, all sensors can be divided into two domains according to actual requirements in the same network topology structure, so that the condition that all sensors require to support hardware timestamps is avoided, and the cost is reduced. Separate control of software timestamps and hardware timestamps is achieved through domain management.

In the embodiment of the application, a field timestamp is customized in a PTP message to distinguish the category of the timestamp. When the sensor accesses the network, whether the sensor needs to support hardware time stamping is identified through the field. As shown in fig. 8, sensors are classified into two categories according to whether hardware time stamping is supported: dark colors indicate hardware timestamps are supported and light colors indicate software timestamps only. When a certain sensor is accessed to the network, the sensor can automatically negotiate with peripheral sensors, and a proper sensor is selected as a previous-stage node of clock synchronization. If a sensor supporting hardware time stamp accesses the network, but the upper level sensor node does not support the hardware time stamp, the sensor is refused to access. Therefore, all the sensors on the same link can be ensured to be in the same type (high clock precision or low time precision), and the influence of the low-precision sensors on the high-precision sensors is avoided.

In some optional implementations of this embodiment, when one sensor fails, how the clock synchronization network implements adaptive adjustment. Assuming that the initial state of the sensor connection is as shown in fig. 4, when the sensor C5 has a fault, since the sensor C8 uses the sensor C5 as a master clock, when the sensor C8 continuously sends no response to the message sent by the sensor C5 three times and the duration exceeds 5S, the sensor C8 determines that the sensor C5 has a fault, closes the node connected to the sensor C5, sets the node state from S to P, and at the same time, the sensor C8 sends a negotiation message to the peripheral sensors, finally selects the sensor C7 as a new master clock by the BMCA algorithm, sets the node state connected to the sensor C7 to S, and the result is as shown in fig. 9.

In some optional implementations of this embodiment, it is assumed that an initial state is shown in fig. 4, when a new sensor C10 needs to be added, the sensor sends a multicast message to a peripheral sensor, it is assumed that there are sensors C7, C8, and C9 that can be selected in the periphery, through a BMCA algorithm, the sensor C8 is finally selected as a master clock, a node state connected to C8 is set to S, and a state connected to the sensors C7 and C9 is set to P, and as a result, the result is shown in fig. 10.

In order to solve the technical problem, the embodiment of the application further provides equipment. Referring to fig. 13, fig. 13 is a block diagram of a basic structure of the device according to the present embodiment.

The device 300 is a computer device that includes a memory 310, a processor 320, and a network interface 330 communicatively coupled to each other via a system bus. It is noted that only device 300 having components 310 and 330 is shown, but it is understood that not all of the illustrated components are required and that more or fewer components may alternatively be implemented. As will be understood by those skilled in the art, the computer device is a device capable of automatically performing numerical calculation and/or information processing according to a preset or stored instruction, and the hardware includes, but is not limited to, a microprocessor, an Application Specific Integrated Circuit (ASIC), a Programmable Gate Array (FPGA), a Digital Signal Processor (DSP), an embedded device, and the like.

The computer device can be a desktop computer, a notebook, a palm computer, a cloud server and other computing devices. The computer equipment can carry out man-machine interaction with a user in a keyboard mode, a mouse mode, a remote controller mode, a touch panel mode or a voice control equipment mode.

The memory 310 includes at least one type of readable storage medium including a flash memory, a hard disk, a multimedia card, a card type memory (e.g., SD or DX memory, etc.), a Random Access Memory (RAM), a Static Random Access Memory (SRAM), a Read Only Memory (ROM), an Electrically Erasable Programmable Read Only Memory (EEPROM), a Programmable Read Only Memory (PROM), a magnetic memory, a magnetic disk, an optical disk, etc. In some embodiments, the storage 310 may be an internal storage unit of the device 300, such as a hard disk or a memory of the device 300. In other embodiments, the memory 310 may also be an external storage device of the device 300, such as a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) Card, a Flash memory Card (Flash Card), or the like, provided on the device 300. Of course, the memory 310 may also include both internal and external memory units of the device 300. In this embodiment, the memory 310 is generally used for storing computer readable instructions of an operating system and various types of application software installed in the device 300, such as a clock synchronization method of an in-vehicle sensor. In addition, the memory 310 may also be used to temporarily store various types of data that have been output or are to be output.

The processor 320 may be a Central Processing Unit (CPU), controller, microcontroller, microprocessor, or other data Processing chip in some embodiments. The processor 320 is generally operative to control overall operation of the device 300. In this embodiment, the processor 320 is configured to execute computer readable instructions stored in the memory 310 or process data, such as computer readable instructions for executing a clock synchronization method of the vehicle-mounted sensor.

The network interface 330 may include a wireless network interface or a wired network interface, and the network interface 330 is generally used to establish a communication connection between the device 300 and other electronic devices.

According to the equipment provided by the application, the vehicle-mounted sensor adopts a distributed mesh topology structure, compared with the existing mainstream centralized bus topology structure, the flow is dispersed in independent subnets, the influence of network jitter on synchronization based on a PTP clock can be reduced, the influence of network congestion is effectively reduced, meanwhile, the flexibility of network wiring is increased, the deployment space and the degree of freedom of the sensor are expanded, and the robustness of a system is improved; in addition, the clock source of the reference clock can be automatically switched according to the signal intensity, so that the sensors can still normally work, and the stability of the device is improved.

The present application provides yet another embodiment, which is to provide a storage medium storing computer readable instructions executable by at least one processor to cause the at least one processor to perform the steps of the method for clock synchronization of an in-vehicle sensor as described above.

According to the storage medium, the vehicle-mounted sensor adopts a distributed mesh topology structure, compared with a current mainstream centralized bus topology structure, the storage medium disperses flow in independent subnets, can reduce the influence of network jitter on clock synchronization based on PTP (precision time protocol), effectively reduces the influence of network congestion, increases the flexibility of network wiring, expands the deployment space and the degree of freedom of the sensor, and improves the robustness of a system; in addition, the clock source of the reference clock can be automatically switched according to the signal intensity, so that the sensors can still normally work, and the stability of the device is improved.

Through the above description of the embodiments, those skilled in the art will clearly understand that the method of the above embodiments can be implemented by software plus a necessary general hardware platform, and certainly can also be implemented by hardware, but in many cases, the former is a better implementation manner. Based on such understanding, the technical solutions of the present application or portions thereof that contribute to the prior art may be embodied in the form of a software product, where the computer software product is stored in a storage medium (such as a ROM/RAM, a magnetic disk, and an optical disk), and includes several instructions for enabling a terminal device (which may be a mobile phone, a computer, a server, an air conditioner, or a network device) to execute the method according to the embodiments of the present application.

It is to be understood that the above-described embodiments are merely illustrative of some, but not restrictive, of the broad invention, and that the appended drawings illustrate preferred embodiments of the invention and do not limit the scope of the invention. This application is capable of embodiments in many different forms and is provided for the purpose of enabling a thorough understanding of the disclosure of the application. Although the present application has been described in detail with reference to the foregoing embodiments, it will be apparent to one skilled in the art that the present application may be practiced without modification or with equivalents of some of the features described in the foregoing embodiments. All equivalent structures made by using the contents of the specification and the drawings of the present application are directly or indirectly applied to other related technical fields and are within the protection scope of the present application.

Claims (10)

1. A method for clock synchronization of a vehicle-mounted sensor, comprising the steps of:

after receiving a time synchronization trigger instruction, carrying out initialization operation on a reference clock to obtain an initialized reference clock;

acquiring signal intensity information of an external clock in real time;

if the signal intensity information meets a preset signal intensity threshold value, performing first synchronous operation on the initialization reference clock according to the external clock to obtain a first synchronous reference clock;

if the signal intensity does not meet the preset signal intensity threshold value, performing second synchronous operation on the initialization reference clock according to a local clock to obtain a second synchronous reference clock;

and performing the second synchronization operation on the vehicle-mounted sensors according to the first synchronization reference clock or the second synchronization reference clock, wherein the vehicle-mounted sensors are topologically connected according to a mesh topology structure.

2. The clock synchronization method of the vehicle-mounted sensor according to claim 1, wherein if the signal strength information satisfies a preset signal strength threshold, the method further comprises, after the step of obtaining a first synchronization reference clock, performing a first synchronization operation on the initialization reference clock according to the external clock:

and performing the second synchronization operation on the local clock according to the first synchronization reference clock.

3. The clock synchronization method for the vehicle-mounted sensor according to any one of claims 1 or 2, characterized in that the second synchronization operation is realized based on a PTP clock synchronization principle.

4. The clock synchronization method of the vehicle-mounted sensor according to claim 1, wherein the vehicle-mounted sensor comprises a hardware timestamp type and a software timestamp type, and the vehicle-mounted sensor is topologically linked with the same region according to the hardware timestamp type or the software timestamp type.

5. A clock synchronization apparatus of a vehicle-mounted sensor, comprising:

the initialization module is used for initializing the reference clock after receiving the time synchronization triggering instruction to obtain an initialized reference clock;

the signal acquisition module is used for acquiring signal intensity information of an external clock in real time;

the first reference clock synchronization module is used for carrying out first synchronization operation on the initialization reference clock according to the external clock to obtain a first synchronization reference clock if the signal intensity information meets a preset signal intensity threshold;

the second reference clock synchronization module is used for performing second synchronization operation on the initialization reference clock according to a local clock to obtain a second synchronization reference clock if the signal strength does not meet the preset signal strength threshold;

and the sensor synchronization module is used for performing the second synchronization operation on the vehicle-mounted sensor according to the first synchronization reference clock or the second synchronization reference clock, wherein the vehicle-mounted sensor performs topology connection according to a mesh topology structure.

6. The clock synchronization apparatus of an in-vehicle sensor according to claim 5, further comprising:

and the local clock synchronization module is used for carrying out the second synchronization operation on the local clock according to the first synchronization reference clock.

7. The clock synchronization device for the in-vehicle sensor according to claim 5, wherein the second synchronization operation is realized based on a PTP clock synchronization principle.

8. The clock synchronization device for the vehicle-mounted sensor according to claim 5, wherein the vehicle-mounted sensor comprises a hardware timestamp type and a software timestamp type, and the vehicle-mounted sensor performs the local topology linking according to the hardware timestamp type or the software timestamp type.

9. An apparatus comprising a memory having computer readable instructions stored therein and a processor which when executed implements the steps of the method of clock synchronization of an in-vehicle sensor according to any of claims 1 to 4.

10. A storage medium, characterized in that it has stored thereon computer-readable instructions which, when executed by a processor, implement the steps of a method for clock synchronization of a vehicle-mounted sensor according to any one of claims 1 to 4.

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