JP2010085325A - Time synchronizer, program for performing computer as time synchronizer, and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a time synchronizer maintaining accuracy of an internal clock by selecting a time information server for synchronizing depending on a time difference between the internal clock and the time information server. <P>SOLUTION: A control part 101 takes a first current time T1 from a time information source 200 and a second current time T2 from a time information source 300 respectively, corrects the time of the internal clock based on the current time T1 in cases where the time difference between a time T0 of the internal clock and the current time T1 is equal or higher than a predetermined threshold, and corrects the time of the internal clock based on the current time T2 in other cases. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a time synchronization apparatus, an electronic apparatus using the same, a program for causing a computer to function as a time synchronization apparatus (hereinafter referred to as “time synchronization program”), and a computer-readable record storing the time synchronization program. In particular, the present invention relates to a time synchronization apparatus that acquires the current time from different time information sources and corrects the time of the internal clock, a time synchronization program, and a recording medium.

  Currently, many devices are used that hold a clock (internal clock) inside, acquire time information from an external time information source, and correct the time.

  For example, in a digital broadcast receiver, data called TOT (Time Offset Table) including information on the current time is multiplexed in a digital broadcast wave, and the digital broadcast is received by acquiring this data when the broadcast wave is received. The internal clock in the machine can be corrected. The synchronization of the internal clock when a plurality of TOTs can be acquired by receiving a plurality of digital broadcasts is disclosed, for example, in Patent Document 1 below. Using the method described in Patent Document 1, it is possible to select one TOT from a plurality of TOTs and synchronize the internal clock with the current time of the selected TOT. In addition, in a device connected to the network, for example, by implementing SNTP (Simple Network Time Protocol) defined in RFC2030, the time information server packet transmission time, the device packet reception time, etc. The internal clock can be corrected.

JP 2007-116321 A

  The technique disclosed in Patent Document 1 described above is accurate (defined as close to a true value) and precision (small variation) as TOT transmitted multiplexed with a digital broadcast wave. However, it is assumed that any digital broadcast wave is within a certain range.

  However, if there is a device that does not have a means for acquiring time information with high accuracy and precision, such as Japan Standard Time transmitted by TOT or standard radio waves, or in a place where the device cannot be acquired, for example, a network Although there is a method of acquiring the current time from the time information server via the time information server, the accuracy and precision are the same for all time information servers due to differences in the configuration of the time information server and the protocol for acquiring the time information. May not be guaranteed. In such a case, there is a possibility that the accuracy cannot be maintained if the internal clock is synchronized with a time information server that has high accuracy but is not guaranteed to have high accuracy. In addition, if the internal clock is synchronized with a time information server with low accuracy but guaranteed accuracy, there is a problem that it is difficult to maintain accuracy.

  The present invention has been made to solve the above-described problems and the like, and one of the objects of the present invention is to provide a time synchronization device that maintains at least the accuracy of the internal clock.

  In order to solve the above problem, a time information server to be synchronized is selected according to a time difference between the internal clock and the time information server.

  According to one aspect of the present invention, in a time synchronization apparatus that corrects the time of an internal clock based on current times acquired from a plurality of time information sources, the time synchronization apparatus includes a control unit, and the control unit includes: A first current time from the first time information source, a second current time from a second time information source different from the first current time, and the time of the internal clock and the first time If the time difference from the current time is equal to or greater than a predetermined first threshold, the time of the internal clock is corrected based on the first current time, and the time of the internal clock and the first current Provided is a time synchronizer that corrects the time of the internal clock based on the second current time when the time difference from the time is not greater than or equal to the predetermined first threshold. . The second time information source is higher in accuracy than the first time information source, but is not guaranteed to be always high in accuracy, and the first time information source is the second time information source. Compared to the time information source of, the accuracy is low, but it is guaranteed that the accuracy is high.

  The second time information source, which is more accurate than the first time information source but is not guaranteed to be always highly accurate, and the second time information source, which is less accurate but more accurate than the second time information source. If there is a first time information source that is guaranteed to be high, and the time difference between the first time information source and the second time information source is equal to or less than a threshold value, the second time information source As the internal clock synchronizes with each other, the precision and accuracy can be maintained.

  In addition, after it is determined that the time difference between the time of the internal clock and the first current time exceeds the predetermined first threshold, the control unit determines the time of the internal clock and the time of the internal clock. The time of the internal clock may be corrected based on the first current time until a time difference from the second current time is predetermined and equal to or less than a second threshold different from the first threshold. preferable.

  The communication unit further includes a communication unit that transmits and receives data via a network, and the communication unit receives a packet including a current time transmitted from a time information server including a time information source on the network. Preferably, the current time is acquired from the time information source by extracting the current time from the received packet including the current time.

  According to another aspect of the present invention, there is provided a time synchronization method for correcting the time of an internal clock based on current times acquired from a plurality of time information sources, wherein the first current time is determined from a first time information source. Obtaining a second current time from a second time information source different from the first current time, and a time difference between the time of the internal clock and the first current time is determined in advance. If it is equal to or greater than the first threshold, the time of the internal clock is corrected based on the first current time, and the time difference between the time of the internal clock and the first current time is predetermined. If the time is not equal to or greater than the first threshold value, a time synchronization method is provided that includes a step of correcting the time of the internal clock based on the second current time. After it is determined that the time difference between the time of the internal clock and the first current time exceeds the predetermined first threshold, the time of the internal clock and the second current time are It is preferable that the method further includes a step of correcting the time of the internal clock based on the first current time until the time difference is equal to or less than a second threshold that is predetermined and different from the first threshold.

  The present invention may be a program for causing a computer to execute the above method, or a computer-readable recording medium on which the program is recorded. The program may be in a form that can be acquired by a transmission medium such as the Internet.

  According to the time synchronization apparatus of the present invention, the first current time is obtained from the first time information source, the second current time is obtained from the second time information source, and the time of the internal clock and the first time are obtained. If the time difference from the current time is greater than or equal to a predetermined threshold, the internal clock time is corrected based on the first current time, otherwise the internal clock time is corrected based on the second current time. To do.

  Therefore, the second time information source, which is more accurate than the first time information source but is not guaranteed to be always highly accurate, is less accurate but more accurate than the second time information source. If there is a first time information source that is guaranteed to be high, if the time difference between the first time information source and the second time information source is less than or equal to a threshold value, the second time The accuracy and accuracy can be maintained by synchronizing the internal clock with the information source.

  Further, if the time difference is equal to or greater than the threshold value, at least accuracy can be maintained by synchronizing the internal clock with the first time information source.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

<First Embodiment>
FIG. 1 is a functional block diagram showing an internal configuration example of the time synchronization apparatus 100 according to the first embodiment of the present invention. FIG. 2 is a flowchart showing the flow of processing in the control unit 101 of the time synchronization apparatus 100 according to this embodiment.

  This embodiment will be described with reference to FIG. 1 and FIG. The time synchronization apparatus 100 can be applied to any apparatus having an internal clock, such as a television receiver, STB, DVR (Digital Video Recorder), PC (Personal Computer), etc. .

  In FIG. 1, a time synchronization apparatus 100 includes a control unit 101 that controls the operation of the time synchronization apparatus 100, a storage unit 102 that stores a control program 180, a timer unit 103 that generates the time of an internal clock, And a communication unit 104 that is a communication interface having a function of transmitting and receiving data via a network.

  The control unit 101 includes a microprocessor, an FPGA (Field Programmable Gate Array), which is a programmable LSI (Large Scale Integration), and an ASIC (Application, which is an integrated circuit designed and manufactured for a specific application. Specific Integrated Circuit), a circuit having other arithmetic functions, or the like may be used.

  The storage unit 102 may be any medium or circuit that can hold data, such as a hard disk or a flash memory. The storage unit 102 also stores a control program 180 for causing the control unit 101 to perform predetermined processing. The control unit 101 can perform various types of processing, arithmetic processing, and the like for each component within the time synchronization apparatus 100 according to the control program 180.

  The timer unit 103 performs time management based on a clock included in the time synchronization apparatus 100. For example, when the value of the current time is set from the control unit 101, the current time is then incremented from time to time based on a clock output from a clock generator such as a crystal oscillator. Can be held.

  Communication methods used in the communication unit 104 include short-range wireless communication technologies such as Bluetooth (registered trademark of Bluetooth SIG), IEEE802.11a, IEEE802.11b, IEEE802.11g, and other UWB standards for wireless LAN. Either a wireless communication technology or a communication interface for performing data communication using a wired LAN standard such as Ethernet (registered trademark of Xerox), IEEE 1394, HDMI, PLC, or the like may be used.

  Hereinafter, the time synchronization process performed between the time synchronization apparatus 100 and the external first and second time information sources 200 and 300 will be specifically described with reference to FIGS. 1 and 2. The first time information source 200 is lower in accuracy than the time information source 300 (for example, the time information is in units of minutes) but high in accuracy (for example, transmitted by a standard radio wave or a radio wave from a GPS satellite). The second time information source 300 is higher in precision than the first time information source 200 (for example, the time information). Although the information is in seconds, it is not guaranteed that the accuracy is always high (for example, in the case of an NTP server, the accuracy is due to overload due to concentration of time queries from NTP clients, communication interruption with the upper NTP server, etc.) ) It shall be a time information source.

  Alternatively, the present invention is applied to the case where synchronization to the first time information source 200 is indispensable in the operational specifications of the time synchronization apparatus 100, and synchronization to the second time information source 300 is optional. Is possible. When the second time information source 300 has higher precision than the first time information source 200, the first time information source 200, the second time information source 300, and the like are applied by applying the present invention. If the time difference is equal to or smaller than the threshold value, the internal clock is synchronized with the second time information source 300, so that the synchronization with the first time information source 200 can be maintained while maintaining the precision. .

  Further, the process of the time synchronization apparatus 100 described below is executed by the control unit 101 operating according to the control program 180 stored in the storage unit 102. This will be described with reference to FIGS.

  When the process is started, as shown in FIG. 2 (step S1), the control unit 101 of the time synchronization apparatus 100 initializes the time synchronization process (sets the flag to FALSE) when the apparatus is activated. Perform the following processing.

  The control unit 101 acquires the current time (first current time) T1 from the external first time information source 200 (step S2). When the first time information source 200 exists on the network, the communication unit 104 receives a data packet including the first current time T1 transmitted by the first time information source 200, and the control unit 101 The first current time T1 is extracted from the data packet received by the communication unit 104. When the first time information source 200 transmits a data packet by unicast, the communication unit 104 transmits a data packet transmission request to the first time information source 200 in advance. Note that the timing for acquiring the first current time T1 may be acquired at predetermined intervals, for example, or any request from the user to the time synchronization apparatus 100 (for example, the television receiver). In such a case, it may be acquired when a program guide display request, a content reproduction request, or the like) occurs.

  If the flag is TRUE in step S3 (Y in step S3: That is, the time difference between the current time T0 of the internal clock and the first current time T1 acquired from the first time information source 200 is equal to or greater than the first threshold Th1. Since the time difference between the current time T0 of the internal clock and the second current time T2 acquired from the second time information source 300 exceeds the second threshold Th2), the first time information source Based on the first current time T1 acquired from 200, the time of the internal clock is corrected (step S6).

  If the flag is not TRUE in step S3 (N in step S3), the control unit 101 acquires the current time T0 of the internal clock from the timer unit 103, and the current time T0 of the internal clock and the first time information source 200. The time difference from the first current time T1 acquired from the above is obtained, and it is determined whether or not the time difference is equal to or greater than a predetermined first threshold Th1 (step S4). As the value of the threshold Th1, for example, if it is set to be 2 to 3 times the maximum rounding error of the time information acquired from the first time information source 200, before it deviates significantly from the time of the first time information source 200, It is possible to synchronize the internal clock with the first time information source 200.

  If the time difference is greater than or equal to the first threshold Th1 in (Step S4), the control unit 101 thereafter uses the first current time T1 acquired from the first time information source 200 to The time is corrected (step S6). Therefore, if the time difference between the current time T0 of the internal clock and the first current time T1 acquired from the first time information source 200 is greater than or equal to the first threshold Th1 in step S4, a flag is set in step S5. Change to TRUE.

  As a time correction method, in addition to the method of simply setting the first current time T1 as the current time T0 of the internal clock, the time synchronization is completed after n minutes (T1-T0) / (n × 60). There is a method of mitigating the time change of the internal clock by adding to the time of the internal clock every second. If the time difference between the current time T0 of the internal clock and the first current time T1 acquired from the first time information source 200 is less than or equal to the maximum rounding error of the time information acquired from the first time information source 200, There is also a method of not performing time correction in order to prevent the influence of the rounding error from reaching the time of the internal clock.

  Therefore, the accuracy is higher than that of the first time information source 200, but the accuracy is higher than that of the second time information source 300 and the second time information source 300, which are not guaranteed to be always high. A state in which the time difference between the first time information source 200 and the second time information source 300 is equal to or greater than a threshold when there is a first time information source 200 that is low but guaranteed to have high accuracy. If so, the time difference between the internal clock synchronized with the second time information source 300 and the second time information source 200 is also equal to or greater than the threshold value, so the internal clock is synchronized with the second time information source 200. By doing so, it is possible to maintain at least accuracy.

  After step S6 or when the time difference is not greater than or equal to the first threshold Th1 in step S4 (N), the control unit 101 obtains the second current time T2 from the external second time information source 300. Obtain (step S7).

  When the time information source 300 exists on the network, the second current time T2 can be extracted using the communication unit 104 as in (Step S2). The timing for acquiring the second current time T2 may be acquired at predetermined intervals, for example, or any request from the user to the time synchronization apparatus 100 (for example, a program table display request in the case of a television). Or a content playback request, etc.), or at the same time as the acquisition of the first current time T1.

  When the flag is FALSE in step S8 (N in step S8, that is, the time difference between the current time T0 of the internal clock and the first current time T1 acquired from the first time information source 200 is the first time difference. The time of the internal clock is corrected based on the second current time T2 acquired from the second time information source 300 (step S11). If the flag is TRUE in step S8 (Y in step S8), a time difference between the current time T0 of the internal clock and the second current time T2 acquired from the second time information source 300 is obtained, and this time difference is determined in advance. It is determined whether it is less than or equal to the second threshold value Th2 (step S9). As for the time difference, when the timings for obtaining the first current time T1 and the second current time T2 are the same, the time difference between the first current time T1 and the second current time T2 is obtained. It may be. As the value of the threshold Th2, for example, when the maximum rounding error + α of time information acquired from the second time information source 200 is set, the time difference between the first time information source 200 and the second time information source 300 is set. After the time becomes sufficiently small, the internal clock can be synchronized with the second time information source 300. When the time difference is equal to or smaller than the second threshold value Th2 in step S9, the control unit 101 changes the flag to FALSE in step S10. Thereafter, the time of the internal clock is corrected based on the second current time T2 acquired from the second time information source 300 (step S11). In the case of N in step S9, or after the internal clock is corrected in step S11, the process returns to step S2.

  Therefore, the accuracy is higher than that of the first time information source 200, but the accuracy is higher than that of the second time information source 300 and the second time information source 300, which are not guaranteed to be always high. If there is a first time information source 200 that is low but guaranteed to have high accuracy, the time difference between the first time information source 200 and the second time information source 300 is less than a threshold value. Since the time difference between the internal clock synchronized with the first time information source 200 and the second time information source 300 is also less than the threshold value, the internal clock is synchronized with the second time information source 300. Precision and accuracy can be maintained.

  Hereinafter, more specific examples will be described. If the time difference between the internal clock and the first time information source is equal to or greater than α (eg, t × 3), the time difference between the internal clock and the second time information source is equal to or smaller than β (eg, t × 2). The internal clock is synchronized with the first time information source until. Otherwise, the internal clock is synchronized with the second time information source. Here, t is the maximum rounding error of the first time information source. Thus, in a state where there is no time difference between the first time information source and the second time information source, the precision and accuracy can be maintained by synchronizing the internal clock with the second time information source. it can. In a state where a time difference between the first time information source and the second time information source is generated, at least accuracy can be maintained by synchronizing the internal clock with the first time information source.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. In the present embodiment, an example is shown in which the time synchronization function in the first embodiment is applied to an electronic device, here a personal computer (hereinafter referred to as a PC). In that case, the program may be read from the recording medium on which the control program 180 for exhibiting the time synchronization function shown in FIG. 1 is recorded, installed in the PC, and the PC or the like is operated based on the program. Detailed description will be given below.

  FIG. 3 is a functional block diagram showing an internal configuration example of a PC 500 having a time synchronization function according to the second embodiment of the present invention.

  FIG. 3 also shows a recording medium 555 for explanation, but this is not an essential requirement. FIG. 3 shows a configuration example when the control program 180 is installed in the PC 500. In this case, the PC 500 also operates as the time synchronization apparatus 100.

  In FIG. 3, a PC 500 includes a control unit 510 having a function of performing various processes and arithmetic processes for each device inside the PC 500, a storage unit 520 such as an HDD or an EPROM in which a control program 180 and the like are stored. An input unit 540 for connecting an interface for a user to perform an input operation on the PC 500, a communication unit 560 for exchanging external time information sources and data, and a timer unit for generating the time of an internal clock 570. The PC 500 is configured to operate according to the control program 180 stored in the storage unit 520.

  Further, the PC 500 controls data access by the control unit 510 and generates a data temporary storage unit 522 used as a work memory for temporarily storing data and an image for displaying font data, graphic data, and the like. A CGROM (Character Graphic Read Only Memory) 534 in which image data used for the image data is stored, and a VDP (Video Display Processor) that reads out necessary image data from the CGROM 534 according to a drawing instruction from the control unit 510 and generates an image. ) 532, a VRAM (Video Random Access Memory) 536 having a function of temporarily storing an image generated by the VDP 532, and a recording medium access having a function of reading the control program 180 from the recording medium 555 in which the control program 180 is recorded. Part 550. The VDP 532 uses the VRAM 536 to generate an image.

  The PC 500 includes a display unit 530 that displays an image based on image data output from the PC 500, a mouse 542 that is an interface for the user to operate the PC 500, and a keyboard that is an interface for the user to operate the PC 500. 544 is connected via the input unit 540. The display unit 530 may be any of display devices that employ other image display methods such as a liquid crystal display, a CRT (Cathode Ray Tube), and a dot matrix.

  The storage unit 520 is accessed by the control unit 510. Note that the storage unit 520 is the same device as the storage unit 102 of the first embodiment.

  The control unit 510 has the same function as that of the control unit 101 of the first embodiment. Therefore, detailed description will not be repeated. The control unit 510 also instructs the VDP 532 to generate an image and display the image on the display unit 530 according to the control program 180 stored in the storage unit 520 (hereinafter, this instruction is referred to as a “drawing instruction”). ).

  The VDP 532 is connected to the display unit 530. The VDP 532 reads out the image data stored in the VRAM 536 and causes the display unit 530 to display an image based on the image data.

  The data temporary storage unit 522 is a high-speed RAM (Random Access Memory), SRAM (Static Random Access Memory), DRAM (Dynamic Random Access Memory), SDRAM (Synchronous DRAM), or double data rate mode capable of temporarily storing data. DDR-SDRAM (Double Data Rate SDRAM), which is an SDRAM having a flexible data transfer function, RDRAM (Rambus Dynamic Random Access Memory: a registered trademark of Rambus), which adopts a high-speed interface technology developed by Rambus, and Direct -RDRAM (Direct Rambus Dynamic Random Access Memory) or any other circuit having a configuration capable of storing and holding data in a volatile manner may be used.

  The control program 180 stored in the recording medium 555 is read from the recording medium access unit 550 and stored in the storage unit 520 by the operation (installation process) of the control unit 510. The recording medium 555 includes a DVD-ROM (Digital Versatile Disk Read Only Memory), a CD-ROM (Compact Disk Read Only Memory), a CF (Compact Flash) card, an SD (Secure Digital) memory card, and a Memory Stick (registered trademark). And a USB memory, a hard disk, a magnetic tape, other volatile recording media, and non-volatile recording media.

  The device in which the control program 180 is recorded is not limited to a PC, and the program can be installed, operates based on the program, and has a function of synchronizing the time of another time information source and the internal clock. Any time synchronization device may be used. For example, the time synchronization device may be a DVR, a television, a mobile phone, or the like.

  The control program 180 may be a program stored on a server device (not shown) that is downloaded via the communication unit 560 and then stored in the storage unit 520.

  An input instruction from the mouse 542 or the keyboard 544 is transmitted to the control unit 510 via the input unit 540. Control unit 510 performs predetermined processing based on an input instruction from input unit 540.

  The communication unit 560 has a function of exchanging data with a network such as the Internet in a wired or wireless manner, and has the same interface as the communication unit 104 described above. The timer unit 570 performs time management based on the clock of the PC 500 and has the same function as the timer unit 103 described above. Detailed description will not be repeated.

  As described above, by using a PC in which the control program 180 is installed, the present invention can be applied even when the time synchronization apparatus 100 described in the first embodiment is realized by a PC. .

  Therefore, also in this embodiment, the same effect as that of the first embodiment can be obtained.

  In addition, it should be thought that embodiment described above is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims. For example, although a case where a PC is used as an application example according to the second embodiment has been described, AV equipment such as a digital broadcast receiving device and a portable music player, home appliances, and a mobile phone because it includes a communication function. It is suitable for use in portable electronic devices.

  FIG. 4 is a diagram illustrating a configuration example of a system according to the present embodiment. In the example illustrated in FIG. 4, a digital broadcast receiving device 100 a including the time synchronization device 100 and the internal clock 103 in the time synchronization device 100 performs time synchronization between the time information source A and the time information source B. . The time information source A is, for example, an SNTP server, and provides the first current time in units of seconds, for example. The time information source B is, for example, a license server, and the second current time is, for example, the first current time. Provide in minutes with less precision. When the digital broadcast is being received, the internal clock 103 is synchronized with the current time included in the TOT in the digital broadcast wave. When the digital broadcast is not received, the time information source A and the time information source are synchronized. The current time may be received from B.

  The present invention can be used for a time synchronization device and an electronic device using the time synchronization device.

It is a functional block diagram which shows the example of an internal structure of the time synchronizer 100 in the 1st Embodiment of this invention. It is a flowchart figure which shows the flow of a process of the time synchronizer 100 in this Embodiment. It is a functional block diagram which shows the example of an internal structure of PC500 in the 2nd Embodiment of this invention. It is a figure which shows the example of 1 structure of the time synchronization system by this Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Time synchronization apparatus, 101, 510 ... Control part, 102,520 ... Memory | storage part, 103,570 ... Timer part, 104,560 ... Communication part, 530 ... Display part, 540 ... Input part, 180 ... Control program, 500 ... PC, 522 ... Temporary data storage unit, 532 ... VDP, 534 ... CGROM, 536 ... VRAM, 542 ... Mouse, 544 ... Keyboard, 550 ... Storage medium access unit, 555 ... Recording medium.

Claims (9)

In the time synchronization device that corrects the time of the internal clock based on the current time acquired from a plurality of time information sources,
The time synchronization apparatus has a control unit,
The control unit
Obtaining a first current time from a first time information source and a second current time from a second time information source different from the first current time,
If the time difference between the time of the internal clock and the first current time is greater than or equal to a predetermined first threshold, the time of the internal clock is corrected based on the first current time,
When the time difference between the time of the internal clock and the first current time is not equal to or more than the predetermined first threshold, the time of the internal clock is corrected based on the second current time. A time synchronizer characterized by the above.   The second time information source is higher in accuracy than the first time information source, but is not guaranteed to be always high in accuracy, and the first time information source is the second time information source. The time synchronizer according to claim 1, wherein the time synchronizer is low in precision but high in accuracy as compared with the time information source. The controller is
After determining that the time difference between the time of the internal clock and the first current time exceeds the predetermined first threshold, the time of the internal clock and the second current time are The time of the internal clock is corrected based on the first current time until the time difference is predetermined and equal to or less than a second threshold different from the first threshold. 2. The time synchronizer according to 2. Furthermore, it has a communication unit that transmits and receives data via the network,
The communication unit receives a packet including a current time transmitted from a time information server including a time information source on a network,
4. The time according to claim 1, wherein the control unit acquires the current time from the time information source by extracting the current time from the received packet including the current time. 5. Synchronizer.   The apparatus provided with the time synchronizer of any one of Claim 1. A time synchronization method for correcting the time of the internal clock based on the current time acquired from a plurality of time information sources,
Obtaining a first current time from a first time information source and a second current time from a second time information source different from the first current time;
If the time difference between the time of the internal clock and the first current time is equal to or greater than a predetermined first threshold, the time of the internal clock is corrected based on the first current time, A step of correcting the time of the internal clock based on the second current time when the time difference between the time of the clock and the first current time is not equal to or greater than the predetermined first threshold; A time synchronization method characterized by the above.   After it is determined that the time difference between the time of the internal clock and the first current time exceeds the predetermined first threshold, the time of the internal clock and the second current time are The method further comprises a step of correcting the time of the internal clock based on the first current time until the time difference is equal to or less than a second threshold that is predetermined and different from the first threshold. Item 7. The time synchronization method according to item 6.   A program for causing a computer to execute the method according to claim 6 or 7.   A computer-readable recording medium on which the program according to claim 8 is recorded.

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