JP2021106328A - Synchronization control device and method - Google Patents

Abstract

To maintain highly accurate synchronization in a time synchronization system.SOLUTION: A synchronization control device performs a synchronization process with a plurality of time sources, obtains a plurality of first times synchronized by the synchronization process, determines whether the state of synchronization with each of the plurality of time sources satisfies a predetermined condition, selects one of the first times whose state of synchronization is determined to satisfy the predetermined condition, and corrects the second time delivered to a slave device based on the selected first times.SELECTED DRAWING: Figure 6

Description

The present invention relates to a synchronization control device and a method for synchronizing a plurality of devices.

Recently, a technique of installing a plurality of cameras at different positions to perform synchronous shooting from multiple viewpoints and generating virtual viewpoint contents using the multiple viewpoint images obtained by the shooting has attracted attention. By using the virtual viewpoint content, for example, the highlight scenes of soccer and basketball can be viewed from various angles, so that the user can be given a high sense of presence as compared with a normal image. In order to generate such virtual viewpoint contents, a time synchronization system for realizing highly accurate synchronized shooting by a plurality of cameras is required. In addition, time synchronization within the network is one of the important technologies even in networks that require accurate timing such as financial transactions and mobile phones.

Patent Document 1 describes a method of selecting which master device to synchronize with in a time synchronization system including a plurality of synchronization master devices. Patent Document 1 proposes to extend BMCA (Best Master Clock Algorism) described in IEEE1588. Specifically, Patent Document 1 describes a method of selecting an optimum master device by incorporating the quality of the network between the master device and the device that synchronizes with the master device into the BMCA.

Japanese Unexamined Patent Publication No. 2016-152489

In a synchronous network system using a boundary clock (hereinafter referred to as BC) corresponding to PTP (Precision Time Protocol), BC performs the following two synchronous processes. The first is the synchronization process between the BC and the time server (synchronization master). BC operates as a slave to the time server in the time synchronization process, and performs the synchronization process for synchronizing with the time of the time server. The second is the synchronization process between the BC and the slave device. In this case, the BC operates as a master for the slave device, and specifically, performs a PTP Sync / Delay Request transmission process.

In a system having a plurality of time servers, BC selects an appropriate time server, performs synchronization processing with the time server, and synchronizes subordinate slave devices based on the synchronization process. In a BC that is already in operation, if the time server cannot be synchronized with the selected time server and the time server is switched immediately, the following problems will occur. That is, when the time correction amount applied on the BC side is not converged by the synchronous processing between the time server and BC, the Sync / Delay Request frame having highly accurate time information is transmitted to the slave device group. You will not be able to. This can be a deterioration factor regarding the synchronization accuracy of the slave device group.

The present invention provides a technique for maintaining highly accurate synchronization in a time synchronization system.

The synchronous control device according to one aspect of the present invention has the following configuration. That is,
An acquisition means that performs synchronization processing with a plurality of time sources and acquires a plurality of first times synchronized by the synchronization processing.
A determination means for determining whether or not the state of synchronization with each of the plurality of time sources by the synchronization process satisfies a predetermined condition.
A selection means for selecting one from the first time when the synchronization state is determined by the determination means to satisfy the predetermined condition.
A correction means for correcting a second time delivered to the slave device based on the first time selected by the selection means is provided.

According to the present invention, a time synchronization system that maintains highly accurate time synchronization is provided.

The figure which shows the configuration example of the image processing system which performs synchronous shooting by a plurality of cameras. The block diagram which shows the functional configuration example of the synchronous control device. The figure explaining the correction process of Real Time Clock. A sequence diagram showing transmission / reception of PTP packets. A sequence diagram showing transmission / reception of PTP packets. A sequence diagram showing transmission / reception of PTP packets. A flowchart showing a synchronization process with a time server by a synchronization control device. A flowchart showing a time server selection process by a synchronous control device. The flowchart which shows the determination process of the synchronization state by a synchronization control device. The flowchart which shows the correction processing of the time information for distribution in a synchronous control device. A flowchart showing the synchronization process with the camera adapter by the synchronization control device.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiment, not all of the plurality of features are essential to the invention, and the plurality of features may be arbitrarily combined. Further, in the attached drawings, the same or similar configurations are designated by the same reference numbers, and duplicate explanations are omitted.

FIG. 1 is a block diagram showing a configuration example of a time synchronization system according to the embodiment. In this embodiment, an image processing system 100 that generates a virtual viewpoint image in a stadium or a concert hall is illustrated. In the image processing system 100, highly accurate time synchronization is required in order to realize synchronized shooting by a plurality of cameras. The image processing system 100 includes a synchronization control device 101, a time server 102a, a time server 102b, a hub 103, a user terminal 104, a control terminal 105, an image computing server 106, and a sensor system (110a-z).

The control terminal 105 manages the operating state and controls the parameter setting for each block constituting the image processing system 100 through the network. Here, the network may be GbE (Gigabit Ethernet) or 10 GbE conforming to the IEEE standard (registered trademark, hereinafter omitted), or may be configured by combining an interconnect Infiniband, an industrial Ethernet, or the like. Further, the network is not limited to these, and may be another type of network.

First, an operation of transmitting image pickup data from the 26 sets of sensor systems 110az to the image computing server 106 will be described. In the present embodiment, unless otherwise specified, the 26 sets of systems from the sensor system 110a to the sensor system 110z are referred to as the sensor system 110 without distinction. Similarly, the devices in each sensor system 110 will be referred to as a camera 112 and a camera adapter 111 without distinction unless otherwise specified. Although the number of sensor systems is described as 26 sets, this is just an example, and the number is not limited to this. Further, the plurality of sensor systems 110 do not have to have the same configuration, and may be configured by, for example, different types of devices. In the present embodiment, unless otherwise specified, the word "image" will be described as including the concepts of moving images and still images. That is, it is assumed that the image processing system 100 of the present embodiment can process both still images and moving images.

The sensor system 110 has one camera 112 each. That is, the image processing system 100 has a plurality of cameras for photographing the subject 108 from a plurality of directions. Although the cameras 112 will be described as being the same, the performance and the model may be different. The plurality of sensor systems 110 are connected to each other by a daisy chain. It is said that this connection form has the effect of reducing the number of connection cables and labor saving in wiring work in increasing the resolution of captured images to 4K or 8K and increasing the capacity of image data due to the increase in frame rate. I will specify it here. However, the connection is not limited to the daisy chain connection, and as a connection form, each sensor system 110 is connected to the hub 103, and a star-type network configuration is performed in which imaging data is transmitted to the image computing server 106 via the hub 103. May be.

Further, FIG. 1 shows a configuration in which all of the sensor systems 110 are daisy-chained, but the present invention is not limited to this. For example, a plurality of sensor systems 110 may be divided into several groups, and the sensor systems 110 may be daisy-chained in the divided group units. Such a configuration is particularly effective in a stadium. For example, a stadium may be composed of a plurality of floors, and a sensor system 110 may be installed on each floor. In this case, the input to the image computing server 106 can be performed for each floor or every half lap of the stadium, and the installation can be simplified even in a place where wiring for connecting all the sensor systems 110 with one daisy chain is difficult. The system can be made flexible.

In this embodiment, the sensor system 110 has a camera 112 and a camera adapter 111. The configuration is not limited to this, and may include, for example, a voice device such as a microphone, a pan head that controls the orientation of the camera, and the like. Further, for example, the sensor system 110 may be composed of one camera adapter and a plurality of cameras, or may be composed of one camera and a plurality of camera adapters. The imaged data captured by the camera 112 is subjected to image processing described later by the camera adapter 111, then transmitted to the hub 103 via the daisy chain connection, and transmitted to the image computing server 106.

The image computing server 106 processes the data acquired from the sensor system 110. First, the imaging data acquired from the sensor system 110 is reconstructed to convert the data format, and then stored according to the camera identifier, data type, and frame number. Then, the designation of the viewpoint is received from the control terminal 105, the corresponding imaging data is read from the information stored based on the received viewpoint, and the rendering process is performed to generate the virtual viewpoint image. The control terminal 105, the sensor system 110, or the user terminal 104 may have at least a part of the functions of the image computing server 106.

The rendered image is transmitted from the image computing server 106 to the user terminal 104, and the user who operates the user terminal 104 can view the image from the viewpoint according to the designation. That is, the image computing server 106 generates virtual viewpoint contents based on the captured images (multi-viewpoint images) captured by the plurality of cameras 112 and the viewpoint information. In the present embodiment, the virtual viewpoint content is generated by the image computing server 106, but the present invention is not limited to this. That is, it may be generated by the control terminal 105 or the user terminal 104.

The time server 102a and the time server 102b as the time source have a function of distributing the time, and distribute the time synchronized with the GPS 107 to the synchronization control device 101. Two time servers are arranged in the system in case an unexpected situation such as a failure occurs in one time server. Hereinafter, when these time servers are generically referred to, they are referred to as time server 102. The synchronization control device 101 transmits a synchronization packet to the sensor system 110 using the time synchronized with the time server 102. The camera adapter 111 in the sensor system 110 that has received the synchronization packet Genlocks the camera 112 based on the time information to perform image frame synchronization. That is, the synchronization control device 101 synchronizes the shooting timings of the plurality of cameras 112. As a result, the image processing system 100 can generate a virtual viewpoint image based on a plurality of captured images taken at the same timing, so that deterioration of the quality of the virtual viewpoint image due to a deviation in the shooting timing can be suppressed.

Next, the functional block of the synchronous control device 101 will be described with reference to FIG. The synchronous control device 101 includes a main control unit 210, a memory 201, a system bus 202, and a communication control unit 220.

The main control unit 210 controls the entire synchronization control device 101. The synchronization processing unit 211a performs synchronization processing using the time server 102a and the Precision Time Protocol (hereinafter, PTP), and obtains the synchronized time (time information 223a). Specifically, it receives an Announce frame, a Sync frame, a Follow Up frame, and a Delay Response frame in the PTP packet transmitted by the time server 102a. In addition, a Delay Request frame is transmitted to the time server 102a. The transmission / reception of these PTP packets between the synchronization control device 101 and the time server 102a is performed using the memory 201 via the port 221a, the packet transfer unit 225, and the packet interface 203. The synchronization processing unit 211a transmits and receives a PTP packet between the time server 102a and the delay amount in the network between the time server 102a and the synchronization control device 101, and an offset amount between the time held by the time server 102a and the time information 223a described later. Is calculated. Then, the synchronization processing unit 211a performs the correction processing of the time information 223a and the correction of the control value of the advance amount of the time information 223a based on the calculation result. These are done via the control interface 204.

The timer 212a is used for the purpose of detecting the timeout of the Sync frame periodically transmitted by the time server 102a. By receiving the Sync frame before the timeout value preset in the timer 212a elapses, it is possible to confirm the existence of the time server 102a. What kind of value is set in the timer 212a is preferably set by referring to the information indicating the transmission frequency information of the Sync frame included in the PTP packet transmitted from the time server 102a. Specifically, the logSyncInterval field included in the Sync frame is available. The synchronization processing unit 211b and the timer 212b have the same functions with respect to the time server 102b.

The time correction unit 213 is responsible for correcting the time information 224 delivered to the slave device based on the time information (time information 223a or time information 223b) selected by the selection unit 216. The operation of this correction process will be described later with reference to FIG. It is desirable that the frequency of correction is the same as the frequency of Sync frames transmitted from the time server 102. As a result, the accuracy of the time information 224 can be expected to be improved according to the frequency of Sync frames of the time server 102. Further, the correction process is executed by accessing the time information 224 using the control interface 204.

The synchronization processing unit 214 is responsible for processing the sensor system 110 as a master of PTP. Specifically, the Unknown frame, the Sync frame, and the Follow Up frame are transmitted to the sensor system 110. Further, when the Delay Request frame is sent from the sensor system 110, the Delay Response frame is transmitted to the corresponding sensor system 110.

The timer 215 is used by the synchronization control device 101 to control the transmission interval of the Unknown / Sync frame to be transmitted to the sensor system 110. The value to be set in the timer 215 may be determined in advance by the system designer. For example, there is a method of logging in to the synchronization control device 101 using Telnet / SSH via a network and setting a value in the timer 215. Further, the synchronization control device 101 may be provided with a user interface for setting, specifically, a keyboard or a monitor, and the user may use the user interface to set the timer 215. In addition to the method of setting the value of the timer 215 from the outside, the synchronization control device 101 may automatically set the value based on the value of the logSyncinterval field included in the Sync frame of the time server 102. The above is the detailed operation of the main control unit 210.

Next, the communication control unit 220 will be described. The communication control unit 220 includes a port 221a, a port 221b, a port 222, a time information generation unit 2230a, a time information generation unit 2230b, a time information generation unit 2240, and a packet transfer unit 225. Port 221a is a connection port with the time server 102a. The packet from the time server 102a is received on the port 221a, and the packet from the synchronization control device 101 to the time server 102a is transmitted from the port 221a. The port 221b is a connection port with the time server 102b, and provides the time server 102b with the same functions as the port 221a. Port 222 is a connection port with the sensor system 110a. The packet from the sensor system 110a is received at port 222, and the packet from the synchronization control device 101 to the sensor system 110a is transmitted from port 222. The time information 223a and the time information 223b are time information possessed by the communication control unit 220.

The time information generation unit 2230a includes a lead amount controller 2231a and an RTC2232a, and generates time information 223a under the control of the synchronization processing unit 211a. The RTC2232a is a real-time clock unit, and generates time information 223a based on, for example, a predetermined reference clock pulse. When the packet received from the time server 102a is a PTP packet, the synchronization processing unit 211a can obtain the time information 223a generated by the RTC2232a as the reception time of the PTP packet. Further, when the packet transmitted from the packet transfer unit 225 to the time server 102a is a PTP packet, the synchronization processing unit 211a can obtain the time information 223a generated by the RTC2232a as the transmission time of the PTP packet. Further, the advance amount controller 2231a has a function of adjusting the gain of the advance amount of the time information 223a generated by the RTC2232a. This function is also used by the synchronization processing unit 211a. For example, the synchronization processing unit 211a can adjust the gain (advance amount) of the advance amount controller 2231a in the synchronization processing based on the correction amount described later. By adjusting the advance amount, the synchronized time information 223a can be obtained from the time information generation unit 2230a (from RTC2232a). The time information generation unit 2230b, the advance amount controller 2231b, and the RTC2232b have the same configuration as the time information generation unit 2230a, the advance amount controller 2231a, and the RTC2232a. Hereinafter, when the subscripts a and b are omitted (time information generation unit 2230, advance amount controller 2231, RTC2322, time information 223), they are collectively referred to.

Here, the operation of the RTC2232 and the lead amount controller 2231 will be described with reference to FIG. In the graph of FIG. 3, the horizontal axis shows the elapsed time from the time, and the vertical axis shows the time actually indicated by each device / element. The time server 102 is illustrated as running ideally. That is, it is assumed that the actual elapsed time and the elapsed time 301 of the time server 102 are in a proportional relationship with the slope "1". The elapsed time 302 of the time information 223 generated by the RTC 2232 elapses with a slope 303 based on the controlled variable of the advance variable controller 2231. The time difference between the time server 102 and the RTC2232, that is, the offset value 305 between the elapsed time 301 and the elapsed time 302 is calculated at the timing when the synchronization processing unit 211 executes the time synchronization processing based on the PTP. The RTC2232 immediately corrects the time information 223 by using the calculated value as a correction value. Further, as described above, the synchronization processing unit 211 corrects the parameter (advance amount gain) of the advance amount controller 2231 based on the calculated value (correction value). As a result, the slope 303 approaches that of the time server according to the number of synchronization processes. The above is the operation of the RTC2232 and the lead amount controller 2231.

Returning to the description of FIG. The time information generation unit 2240 is another time information generation unit possessed by the communication control unit 220, and has the same configuration as the time information generation units 2230a and 2230b. For example, when the packet received from the sensor system 110a is a PTP packet, the synchronization processing unit 214 acquires the time information 223 generated by the RTC 2242 as the reception time of the PTP packet. Further, when the packet transmitted from the packet transfer unit 225 to the sensor system 110a is a PTP packet, the synchronization processing unit 214 acquires the time (time information 224) generated by the RTC 2242 as the transmission time of the PTP packet. The advance amount controller 2241 has a function of adjusting the gain of the advance amount of the time information 224 generated by the RTC 2242, and this function is used by the time correction unit 213.

The packet transfer unit 225 has a function of transmitting a packet created in the memory 201 by the main control unit 210 to the outside via the ports 221a and 221b or the port 222 under the instruction of the main control unit 210. It also has a function of transferring the packet received from the ports 221a and 221b or the port 222 to the memory 201. The above is the configuration of the communication control unit 220 and the synchronization control device 101.

Next, the sequence of synchronization processing of each device will be described with reference to FIG. 4A. The time server 102a and the synchronization control device 101 perform synchronous control communication 410 using PTP packets in a predetermined cycle 420. This cycle 420 is determined based on the information set in the time server 102a. Further, the synchronization control device 101 performs synchronous control communication 470 using the PTP packet with the time server 102b at a predetermined cycle 490. This cycle 490 is determined based on the information set in the time server 102b.

Here, the details of the PTP packets exchanged in the synchronous control communication 410 and the synchronous control communication 470 will be described with reference to FIG. 4B. In the synchronous control communication, the time server 102 first transmits the Sync frame 411. Further, when the synchronization process of the time server 102 is operating in 2steps, the time server 102 transmits the Follow Up frame 412. The synchronization control device 101 that has received the Sync / Follow Up frame transmits the Delay Request frame 413 to the time server 102 when executing the synchronization process. The time server 102 that has received the Delay Request frame 413 transmits the Delay Response frame 414 to the synchronization control device 101.

By transmitting and receiving the above series of PTP packets, the synchronization control device 101 can obtain the times T1 and T4 managed on the time server 102 side and the times T2 and T3 indicated by the time information 223 of the synchronization control device 101. can. From these four time information, the average transmission line delay between the time server 102 and the synchronization control device 101 and the time difference between the time server 102 and the synchronization control device 101, that is, the time correction amount can be obtained as follows. can.
Average transmission line delay = ((T4-T1)-(T3-T2)) / 2
Time correction amount = ((T2-T1)-(T4-T3)) / 2
The above is the exchange of PTP packets between the time server 102 and the synchronization control device 101 in the synchronization control communication 410 and 470.

Returning to the description of FIG. 4A. After executing the synchronous control communication 410 and 470 with the time server 102, the synchronous control device 101 performs the correction processes 415 and 471 of the time information 223, respectively. When the selection unit 216 selects the time server 102a, after the correction process 415 of the time information 223a, the correction process 416 of the time information 224 used for the time synchronization of the slave device (camera adapter 111) is performed by the time correction unit 213. Will be executed.

Next, the processing between the synchronization control device 101 and each camera adapter 111 will be described. The exchange of PTP packets occurs between the synchronization control device 101 and each camera adapter 111 at a cycle of 460 managed by the timer 215. The synchronization processing unit 214, which has detected the passage of a predetermined time from the timer 215, transmits a Sync frame to each camera adapter 111. With this as a trigger, transmission / reception of PTP packets 430 to 450 starts. The PTP packets transmitted and received between the synchronous control device 101 and the camera adapter 111a are the same as those in FIG. 4B. However, in the transmission / reception of PTP packets 430 to 450, the synchronization control device 101 transmits a Sync / Follow Up / Delay Response, and the camera adapter 111a transmits a Delay Request.

Next, the exchange of PTP packets between the synchronization control device 101 and the camera adapter 111b will be described with reference to FIG. 4C. The synchronization control device 101 transmits the Sync frame 441, the Follow Up frame 443, and the Delay Response frame 447 to the camera adapter 111a, which is the same as in FIG. 4B.

The camera adapter 111a transmits the Sync frame 441 received from the synchronization control device 101 to the camera adapter 111b as the Sync frame 442. The camera adapter 111a adds the residence time S1 generated in the camera adapter 111a with respect to the received Sync frame 441 to the Direction field of the Follow Up frame 443 and transmits it to the camera adapter 111b as the Follow Up frame 444. Further, when transmitting the Delay Request frame 445 received from the camera adapter 111b to the synchronization control device 101, the camera adapter 111a adds the residence time S2 in the camera adapter 111a to the Direction field of the Delay Request frame 446 and transmits the delay request frame 445.

As a result, the average transmission line delay between the synchronization control device 101 and the camera adapter 111b and the time correction amount (time difference) can be obtained as follows.
Average transmission line delay = ((T2-T3) + (T4-T1) -S1-S2) / 2
Time correction amount = (T2-T1) -Average transmission line delay-S1

The above is an example in which the camera adapter 111a operates in the End to End (E2E) mode of the transparent clock in the synchronization processing between the synchronization control device 101 and the camera adapter 111b. Although the description is omitted, even if the camera adapter 111a operates in the transparent clock Peer to Peer (P2P) mode, the synchronization processing between the synchronization control device 101 and the camera adapter 111b can be realized. However, it is necessary to unify the mode to E2E or P2P for all camera adapters 111. As a result, even for the camera adapters 111c to z, the relay camera adapters 111b to y operate with the transparent clock, so that the synchronization processing with the synchronization control device 101 can be realized. The above is a description of the exchange of PTP packets in each device.

Next, the synchronization process with the time server 102 by the synchronization control device 101 will be described with reference to FIG. Since the synchronization processing of the synchronization control device 101 is the same for both the time server 102a and the time server 102b, the synchronization processing with the time server 102 will be described here. The synchronization processing unit 211 is responsible for these processes.

First, when the synchronization processing unit 211 receives the Sync frame and the Follow Up frame from the time server 102 (YES in S501), the synchronization processing unit 211 transmits the Delay Request frame to the time server 102 (S502). Then, the synchronization processing unit 211 waits until the Delay Response frame is received from the time server 102 (S503). If the Delay Response frame is not received even after a certain period of time has elapsed (YES in 504), the synchronization processing unit 211 again waits for the reception of the Sync frame from the time server 102 (returns to S501).

Upon receiving the Delay Response frame from the time server 102 (YES in S503), the synchronization processing unit 211 calculates the average transmission line delay and the time correction amount between the time server 102 and the synchronization control device 101 (S505). Then, the synchronization processing unit 211 performs the correction processing of the time information 223 based on the time correction amount (S506). Here, the synchronization processing unit 211 not only corrects the time information 223, but also appropriately corrects the control value of the advance amount controller 2231 to reduce the time correction amount generated each time the synchronization processing is executed. be able to. If this time correction amount can be made sufficiently small, there is a merit when a state (holdover state) in which the PTP packet from the time server 102 to the synchronization control device 101 is temporarily interrupted occurs. This is because the advance amount of the time information 223 of the synchronization control device 101 is close to the advance amount of the time server 102, so that the time information 223 can hold a time close to that of the time server 102 even without time synchronization. ..

After correcting the time information 223, the synchronization processing unit 211 transmits a correction completion notification to the time correction unit 213 and the selection unit 216 (S507). Further, the synchronization processing unit 211 transmits the correction result at that time to the selection unit 216 (S508). As long as the system is operating (YES in S509), the time information 223 is periodically corrected (returns to S501). The above is a description of the synchronization process for the time server 102 of the synchronization control device 101.

Next, the selection method of the time server 102 of the selection unit 216 will be described. Prior to that, the evaluation method regarding whether the synchronization processing between the synchronization control device 101 and the time server 102 is stable / not stable will be described with reference to FIG. explain.

First, the selection unit 216 sets a threshold value of the time correction amount for determining that the synchronization process is stable with respect to the synchronization process with the time server 102 (S701). For example, if it is desired to determine that the synchronization process is stable when the time correction amount of the time information in each synchronization process becomes 200 ns or less, the threshold value is set to 200 ns. This set value may be set according to the synchronization accuracy required for the system. Further, the setting method may be set by the user when the synchronization control device 101 is started, or may be statically incorporated as a design value. Further, this value may be the same value for all time servers, may be changed for each time server, or may be changed according to the time server.

At the timing (YES in S702) when the completion notification of the synchronization processing between the time server X (102a or 102b) and the synchronization control device 101 is received from the synchronization processing unit X (211a or 211b), the process proceeds to the next processing. After receiving the completion notification, the selection unit 216 confirms the time correction amount (S703). Then, the processing branches depending on the magnitude relationship between the time correction amount and the threshold value set in S701. When the time correction amount is smaller than the threshold value, the selection unit 216 determines that the synchronization accuracy is good (YES in S704), and continuously determines that the synchronization process is good for the time server X (hereinafter, the number of determinations). ) Is incremented (S705). Then, when the number of determinations of the synchronization process in the time server X reaches a predetermined number (YES in S706), the selection unit 216 determines that the synchronization with the time server X is stable (707). If the number of determinations has not reached the predetermined number (NO in S706), the selection unit 216 does not determine that the synchronization with the time server X is stable at this point (S708). The predetermined number of times used here may be set by the user or incorporated as a design value of the synchronization control device 101, similarly to the threshold value of the time correction amount (S701).

On the other hand, when the time correction amount is larger than the threshold value, the selection unit 216 determines that the synchronization accuracy with the time server X is poor (NO in S704), and clears the determination number of synchronization processes in the time server X to 0 (NO). S709). Then, at this point, the selection unit 216 determines that the synchronization process with the time server X is "not stable" regardless of the determination results so far (S708). When the system operation is continued (YES in 710), the process returns to S702. The above is the evaluation method regarding "stable / not stable" in the synchronization process between the synchronization control device 101 and the time server 102 according to the present embodiment.

In addition to this, a method of counting the synchronization processing between the synchronization control device 101 and the time server 102 and evaluating that the synchronization is stable when the count value reaches a predetermined number of times may be used. Further, a method may be used in which the synchronization control device 101 and the time server 102 first perform the synchronization processing and then evaluate that the synchronization processing is stable after a lapse of a predetermined time. These methods are inferior in rigor to the evaluation method described with reference to FIG. 7, but have the advantages of simple implementation and light processing. Further, the determination method may be switched according to the synchronization accuracy required for the system. Further, when a certain time elapses when the time server is not selected, the threshold value for determination may be lowered so that the time server can be easily selected. According to such a configuration, it is possible to prevent the time of the synchronization control device 101 and the time of the time server from being endlessly deviated from each other.

The selection unit 216 makes a selection based on the evaluation result of "stable / not stable" in the synchronization process between the time server X and the synchronization control device 101, and the selection procedure is described with reference to FIG. explain.

First, the selection unit 216 does not select any time server (S602) when the synchronization process with the synchronization control device 101 is not stable with any time server (YES in S601). On the other hand, when synchronization is stable with any of the time servers, the time server whose synchronization is stable is selected first (S603). When the time server is selected, the process proceeds to S604 or later.

The selection unit 216 determines whether or not a situation has occurred in which a specific frame cannot be received for a predetermined period from the selected time server for some reason. More specifically, the selection unit 216 determines whether or not a situation has occurred in which the Announce frame or the Sync frame cannot be continuously received a predetermined number of times. When such a situation occurs (YES in S604), the process proceeds to S613. Such a situation occurs, for example, when the link of the line is disconnected, the time server fails, or the power is turned off. It also occurs when PTP packet loss occurs frequently due to an increase in the amount of traffic other than the PTP packet between the time server and the synchronization control device 101, a deterioration in line quality, and the like.

If the Answer frame or Sync frame can be received (NO in S604), the process proceeds to S605. The selection unit 216 determines whether or not the determination result regarding the stability of synchronization with the selected time server has become unstable. If it is determined that the synchronization has become unstable (YES in S605), the process proceeds to S613. For example, it may occur for the same reason as above, when an asymmetric change occurs in the Up / DownLink of the line delay, or when there is a change in the GPS acquisition status of the time server.

In S613 to S616, the selection unit 216 switches from the selected time server to another time server that satisfies a predetermined condition. That is, one is selected from the time information corresponding to the time server whose synchronization state is determined to satisfy a predetermined condition, and the time information delivered to the slave device is corrected based on the selected time information. Will be done. Here, if there is no other time server that satisfies the predetermined condition, none of the time servers is selected. Specifically, when the selection unit 216 has received the Announce frame of the non-selected time server (YES in S613) and the synchronization with the time server is stable (YES in S614), the relevant unit 216 is concerned. A non-selected time server is selected (S615). In this way, the selection unit 216 selects and switches the time information (time server) to be used from the time information (time server) that satisfies the predetermined conditions. In cases other than the above (NO in S613 or NO in S614), it is determined that neither time server is selected (S616). In this case, the synchronization processing unit 214 corrects the time information 224 by continuing to use the time information corresponding to the time server selected until immediately before. Since the selected time server does not exist, the process returns to S601 when the system is continued (YES in S617).

On the other hand, when it is determined that the synchronization with the selected time server is stable (NO in S605), the process proceeds to S606. In S606 to S611, when there are a plurality of selectable time servers, time synchronization is executed with higher accuracy by selecting an appropriate time server from those time servers. First, the selection unit 216 determines whether or not the Announce is received from another time server that is not being selected (S606). When receiving Announcement from another time server (YES in S606), the selection unit 216 determines whether or not the synchronization with the other time server is stable (S607).

When it is determined in S607 that the synchronization with another time server is stable (YES in 607), the selection unit 216 executes the BMCA process (S608) and selects the time server according to the result (S608). S609, S610, S611). The time correction unit 213 corrects the time information 224 using the time information corresponding to the other selected time server. On the other hand, if Announcement from another time server is not received (NO in S606) or synchronization with another time server is not stable (N0 in S607), the selection unit 216 is currently selecting. The time server is continuously selected (S611).

Since BMCA is an existing technology, the explanation is omitted. When the system is continued with any of the time servers selected (YES in S612), the process returns to S604. If the system is continued without selecting any time server (YES in S617), the process returns to S601. The above is the time server selection process by the selection unit 216.

Next, the correction process of the time information 224 in the time correction unit 213 will be described with reference to FIG. The time correction process by the time correction unit 213 indicates that the selection unit 216 has selected the time server (YES in S801) and has received the synchronization completion notification with the selected time server (YES in S802). Executed as a trigger. That is, the time correction unit 213 corrects the time information 224 to be delivered to the slave device based on the time information X (X = 223a or 223b) synchronized by synchronization with the selected time server (S803). When the system operation is continued (YES in S804), the process returns to S801. The above is the processing of the time correction unit 213.

Next, the process required for the synchronization control device 101 to synchronize each camera adapter 111 will be described with reference to FIG. First, the synchronization control device 101 waits until it is time to transmit a Sync frame. The transmission cycle of the Sync frame is managed by the timer 215. When the transmission timing comes (YES in S901), the synchronization control device 101 transmits the Sync frame to each camera adapter 111 (S902). Subsequently, the synchronization control device 101 transmits the follow Up frame to the camera adapter 111 (S903).

After that, the synchronization control device 101 waits for a response from the camera adapter 111 (S904, S905) until the transmission timing of the next Sync frame occurs. When a Delay Request frame is received from the camera adapter 111 (YES in S905), the synchronization control device 101 transmits a Delay Response frame to the corresponding camera adapter 111 (S906). After that, when the transmission timing of the next Sync frame occurs (YES in S904), the process is continued (returns to S902) as long as the event for stopping the system operation does not occur (YES in S907). All the processes up to this point are executed by the synchronous processing unit 214. The above is a description of the processing required for the synchronization control device 101 to synchronize each camera adapter 111.

In the above embodiment, the number of time servers has been described as two, but there may be three or more time servers. In this case, the synchronization control device 101 may provide time information and synchronization processing units for the number of time servers. In addition, as many ports as the number of time servers may be prepared, or a HUB corresponding to a transparent clock may be inserted between the time servers and the synchronization control device to consolidate the ports with the time servers into one port. good. Further, in the above embodiment, the synchronous control device that realizes the synchronous shooting by a plurality of cameras has been described, but the present invention is not limited to this. The synchronous control described in the embodiment can be applied to other networks that require accurate timing, such as financial transactions and mobile phones.

As described above, according to the above embodiment, when the time server 102 needs to be switched in the synchronization control device 101, the accuracy of time synchronization that can occur in the slave device synchronized with the synchronization control device 101. Switching can be performed with reduced deterioration.

The present invention supplies a program that realizes one or more functions of the above-described embodiment to a system or device via a network or storage medium, and one or more processors in the computer of the system or device reads and executes the program. It can also be realized by the processing to be performed. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

The invention is not limited to the above embodiments, and various modifications and modifications can be made without departing from the spirit and scope of the invention. Therefore, a claim is attached to make the scope of the invention public.

101: Synchronous control device, 210: Main control unit, 211a, 211b, 214: Synchronous processing unit, 212a, 212b, 215: Timer, 213: Time correction unit, 216: Selection unit

Claims (15)

An acquisition means that performs synchronization processing with a plurality of time sources and acquires a plurality of first times synchronized by the synchronization processing.
A determination means for determining whether or not the state of synchronization with each of the plurality of time sources by the synchronization process satisfies a predetermined condition.
A selection means for selecting one from the first time when the synchronization state is determined by the determination means to satisfy the predetermined condition.
A synchronous control device comprising: a correction means for correcting a second time delivered to a slave device based on the first time selected by the selection means. The synchronization control device according to claim 1, wherein the acquisition means periodically synchronizes the plurality of first times by the synchronization process. The synchronization control device according to claim 1 or 2, wherein the predetermined condition includes that the first time is synchronized a predetermined number of times by the synchronization process. The synchronization control according to claim 1 or 2, wherein the predetermined condition includes that the first time is after a predetermined time has elapsed since the first synchronization was performed by the synchronization process. Device. The predetermined condition is characterized in that the time difference between the first time and the time of the time source or the time correction amount calculated when synchronizing with the time source is smaller than the threshold value. The synchronous control device according to claim 1 or 2. The synchronous control device according to claim 5, wherein the predetermined condition includes the number of times that the time difference or the time correction amount is determined to be smaller than the threshold value occurs continuously over a predetermined number of times. When a predetermined frame is not received for a predetermined period from the time source corresponding to the first time being selected, the selection means is in the first time when the synchronization state is determined to satisfy the predetermined condition. The synchronous control device according to any one of claims 1 to 6, wherein another first time is selected from the above. The synchronization control device according to claim 7, wherein the predetermined frame is an Announce frame or a Sync frame of the Precision Time Protocol. When the selection means determines that the synchronization state of the first time being selected does not satisfy the predetermined condition, the selection means determines that the synchronization state satisfies the predetermined condition. The synchronous control device according to any one of claims 1 to 6, wherein another first time is selected from the time of the above. When there are a plurality of first times in which the synchronization state is determined to satisfy the predetermined condition, the selection means selects one of the first times determined to satisfy the predetermined condition by BMCA. The synchronous control device according to any one of claims 1 to 9, wherein the synchronous control device is selected according to the above. Any of claims 1 to 10, wherein the selection means does not select any of the first times when the first time determined that the synchronization state satisfies the predetermined condition does not exist. The synchronous control device according to item 1. Any one of claims 1 to 10, wherein the selection means does not select any time source when there is no first time when the synchronization state is determined to satisfy the predetermined condition. Synchronous control device as described in the section. The synchronous control according to claim 12, wherein the correction means corrects the second time based on the first time selected until immediately before, in a state where no time source is selected. Device. An acquisition process in which synchronization processing is performed with a plurality of time sources and a plurality of first times synchronized by the synchronization processing are acquired.
A determination step of determining whether or not the state of synchronization with each of the plurality of time sources by the synchronization process satisfies a predetermined condition.
A selection step of selecting one from the first time determined by the determination step that the synchronization state satisfies the predetermined condition, and
A synchronous control method comprising: a correction step of correcting a second time delivered to a slave device based on the first time selected by the selection step. A program for operating a computer as each means of the synchronization control device according to any one of claims 1 to 13.

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