JP2012211881A - Network apparatus and time synchronizing method in the same apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To periodically synchronize a time without depending on a communication delay or communication states between a master system and a slave system.SOLUTION: Aside from a communication path 23, a transmission path 24 is independently provided for transmitting a synchronization signal from a master system 21A to a slave system 22A such that the master system 21A, after notifying time information via the communication path 23, periodically transmits the synchronization signal for resetting time information of a unit time or later via the transmission path 24 at notified times. The slave system 22A, at a time point of receiving the synchronization signal, resets a time clocked in the interior to the notified time information and restarts the clocking.

Description

  The present invention performs highly accurate time synchronization between a master system that communicates with a time information distribution source to acquire time information, and a slave system that receives time information from the master system and performs time synchronization. The present invention relates to a network device and a time synchronization method in the device.

  FIG. 7A shows a configuration example of a conventional star network system. According to FIG. 7A, this star network system includes wireless devices a1, a2, and a3, an access point A that connects the wireless devices a1, a2, and a3 to an upper network, and a wireless device b1. , B2 and b3 and an access point B which connects the wireless devices b1, b2 and b3 to a higher-level network.

  According to this configuration, each wireless device a1, a2,. a3, b1, b2, and b3 communicate only with one specific access point A (or B). For example, when using a TDMA (Time Division Multiple Access) communication method, each of the access point A (B) and the wireless devices a1, a2, a3 (b1, b2, b3) connected to the access point A (B) Timing control is performed using time information and the like possessed by.

  However, as shown in FIG. 7B, the wireless devices a1, a2, a3, b1, b2, b3 are connected to a plurality of access points A, B for the purpose of improving communication reliability. In the case of a network that can constitute an alternative route, in the case of a network having a so-called communication route redundancy, it is necessary to control the communication timing in the entire network. For example, while the wireless device al is communicating with the access point A, not only the wireless devices a2 and a3 but also the wireless devices b1, b2 and b3 cannot communicate with the access point A. Further, in a frequency hopping network, it is necessary that both wireless devices be set to use the same frequency at the timing of communication. In order to realize this, it is necessary for the access points and wireless devices constituting the network to have common time information, and to control the communication timing and the use frequency according to this time information.

  In addition, even in the simple network configuration without an alternative route shown in FIG. 7A, time synchronization of the entire network is necessary when wireless communication interference is considered. Specifically, in the network configuration shown in FIG. 7A, between access points (for example, between access point A and access point B), between a wireless device and an adjacent access point (for example, wireless device b1 and access point) A) In a situation where communication interference may occur between wireless devices connected to different access points (for example, wireless device a3 and wireless device b1), the communication timing of the entire network may be reduced to avoid interference. Control is required.

  For this reason, in many cases, the conventional time synchronization system installs a time server as a time reference in an upper network to which the access point is connected, and the access point synchronizes time required for communication timing control from the time server. Receive information and relay it to the wireless device. In this way, by synchronizing the time of all the devices constituting the network, it is possible to control the communication timing over the entire network, and it is possible to realize communication interference resolution and power saving control.

  8 and 9 show system configuration examples of a conventional time synchronization system. According to the system configuration shown in FIG. 8, the time synchronization system includes three entities, a time server 400, a master system 301, and a slave system 302, and time synchronization is performed among these entities. Both the master system 301 and the slave system 302 are included in the access point 300. The master system 301 is a part that exchanges time information between the time server 400 and the access point 300. The slave system 302 is a master system. This is a part that receives time information from 301 and notifies this to the wireless network.

  The master system 301 is connected to the time server 400 via the network 401 or the like, and receives time information from the time server 400 using a communication protocol for time synchronization such as NTP (Network Time Protocol) (FIG. 8). A). Next, the master system 301 notifies the slave system 303 of time information synchronized with the time server 400 via the serial communication path 303 (b in FIG. 8), so that the master system 301 and the slave system 302 Time synchronization with the time server 400 is performed.

An example of a format format of a communication frame that propagates between the master system 301 and the slave system 302 at this time is shown in FIG. According to FIG. 10, a command identifier (CMD) for notifying time information is added to time information for synchronization (2010/01/01 /
12: 34: 56: 789) is added. When the slave system 302 receives this communication frame, the slave system 302 updates the internal time information.

  The time synchronization system described above is based on the premise that the slave system 302 cannot acquire time information directly from the time server 400 and must always pass through the master system 301. For example, the time server 400 and the master system 301 are systems having an NTP client function, and the slave system 302 operates in cooperation with the master system 301 and requires time information synchronized with the time server 400 and the master system 301. It is a device. Specifically, the slave system 302 is a sensor module, a wireless module, or the like.

  For example, when the slave system 302 is a sensor module, an operation of sensing by the slave system 302 itself at a certain fixed timing or period, accumulating the result, or notifying the master system 301 can be considered. At this time, in an application that needs to record the sensing time with high accuracy, the slave system 302 needs to maintain time information with high accuracy. When the slave system 302 is a wireless module, the wireless modules that transmit and receive data must be time-synchronized to determine the data transmission / reception timing. In particular, in the TDMA communication method, time synchronization between wireless devices is extremely important, and the accuracy depends on the communication method. As a general usage, a wireless communication timing is determined in synchronization with a reference such as a time server and time information that each wireless module serves as a reference.

  Both the master system 301 and the slave system 302 maintain time information synchronized within the system. Specifically, the quartz resonator or the like built in each system is used as a clock source, and the time information after synchronization is maintained by counting this internally. Generally, an allowable error is defined for a device serving as a clock source, and time information is maintained while including an error depending on the accuracy. As a specific example, a device equipped with a clock having an allowable error of ± 100 ppm may be shifted in time by (60 sec) * (± 100 ppm) = ± 6 ms in one minute. Therefore, in order to maintain the time accuracy required by the system, it is necessary to resynchronize the time information with a frequency corresponding to the accuracy of the clock source as well as one time synchronization.

  Many patent applications have been filed for time synchronization systems that eliminate time lag by resynchronizing time information between devices and perform accurate information processing. For example, Patent Document 1 discloses a technique for performing time adjustment by calculating a delay time generated when a signal is transmitted between a master station and a slave station from a signal transmission time and a signal reception time. . Patent Document 2 discloses a technique for determining the time for data transfer to the other party based on the data transfer time measured in advance and notifying the other party of the time in order to synchronize the time between the computer and the terminal. It is disclosed. In Patent Document 3, the main electronic control unit transmits a set value for time synchronization to another electronic control unit, and when the other electronic control unit receives the set value, the interrupt function is enabled, In particular, there is disclosed a technique for executing an interrupt process for performing time synchronization by receiving a signal transmitted from a main apparatus via the same communication path.

JP-A-5-161181 JP-A-5-216837 Japanese Patent Laid-Open No. 2004-234098

  By the way, in the situation where the slave system requires highly accurate time synchronization with the time server, there are some problems that affect the synchronization accuracy when the conventional time synchronization method is applied. One is that when the time information notification takes a long time due to the specifications of the communication bus connected to the master system and the slave system, or the time required for the notification is not constant, the master system displays the time information shown in FIG. The time information data has already shifted when it arrives at the slave system due to the delay caused by passing through the communication bus while generating the communication frame to notify the slave system and sending it to the slave system. That is.

  Specifically, in a system that requires time synchronization of 1 ms, consider a case where a master system and a slave system are connected with a specification of 38.4 kbps, and a command of 16 octets is required for notification of time information. In this case, it takes time to notify the time information by 16 (octets) × 8 (bit / octet) ÷ 115.2 (bps) = 3.3 (ms). In actual communication, various overheads related to software processing and communication protocols are added to this time. When the time information notified in this situation is set in the slave system as it is, the time synchronization with the accuracy required between the master system and the slave system cannot be established.

  In addition, the same problem occurs when a system that stores time information, such as a real-time clock that maintains time information, is connected separately from the master system 301 and the slave system 302 shown in FIG. . That is, when transmitting and receiving time information directly via a communication bus, a problem can always arise from the viewpoint of time synchronization accuracy.

  On the other hand, when it is guaranteed that the delay is always constant, the synchronization accuracy can be maintained by subtracting this delay when setting the time information in the slave system, but the delay time is not constant Cannot use this method. Specifically, as an example in which the communication delay between the master system and the slave system cannot be estimated in advance, the synchronization information notification data and its application data such as sensor data and wireless data are transmitted and received on the same communication path It is conceivable that time information cannot be notified from the master system side to the slave system at a desired timing because application data is being transmitted / received. As a result, the time required for notification of time information is affected by other communication conditions, and the accuracy of synchronization decreases.

  Further, there may be a case where communication for notification of synchronization information cannot be executed with priority over other communication. This can be avoided by temporarily stopping application communication for notification of time synchronization information. However, in general, time synchronization information is positioned as an auxiliary in communication between the master system and the slave system, that is, communication with a lower priority than sensor data or wireless data originally intended to be communicated between the master systems. It is. For this reason, sending the synchronization information in preference to the application data to be originally communicated may affect the system and application aspects.

  The present invention has been made to solve the above-described problems, and is a network device capable of performing periodic time synchronization without depending on communication delay or communication status between a master system and a slave system, and An object is to provide a time synchronization method in the same device.

  In order to solve the above-described problems, the present invention comprises a master system that communicates with a time information distribution source to acquire time information, and a slave system that receives time information from the master system and performs time synchronization. A network device, wherein a transmission path for transmitting a synchronization signal from the master system to the slave system is provided separately from a communication path for performing communication between the master system and the slave system. A time information transmitter for notifying the slave system of the time information with a unit time accuracy determined in advance via the communication path, and the transmission path at the notified time after notifying the time information. A synchronization signal transmitter for transmitting the synchronization signal for resetting time information of the unit time or less via The slave system, the at the time of reception of the synchronization signal, characterized in that it comprises a time synchronization control unit restarts the timing with the time instant being clocked again set the notification time information internally.

  According to the present invention, apart from the communication path, by providing an independent transmission path for transmitting a synchronization signal from the master system to the slave system, in the master system, after notifying the time information via the communication path, At the notified time, a synchronization signal for resetting time information equal to or less than the unit time is periodically transmitted via the transmission path. In the slave system, when the synchronization signal is received, the time measured internally is reset to the notified time information, and the time measurement is resumed. For this reason, it is possible to avoid a time synchronization shift caused by a delay for notifying time information between the master system and the slave system, and the processing status of the master system or the slave system or the master system and the slave system is determined by the synchronization signal. It is possible to provide a network device capable of exchanging synchronization signals independent of the communication status between the two.

  In the present invention, the accuracy of the unit time is characterized in that the influence of the communication delay can be ignored. According to the present invention, it is possible to avoid a time synchronization shift caused by a delay for notifying time information between the master system and the slave system by using a relatively rough time notification without depending on the accuracy required by the application. be able to.

  In the present invention, the slave system, in the time synchronization control unit, when the time of the slave system is delayed compared to the time of the master system, rounding up the time information below the unit time, When the time of the slave system is advanced compared to the master system, the time information below the unit time is rounded down. According to the present invention, since the time setting is performed by rounding up or down the time information below the unit time, the time setting on the slave system side is facilitated.

  In the present invention, the master system transmits an alignment value not more than the unit time to be set in the slave system after transmitting the next synchronization signal through the transmission path in the synchronization signal transmission unit. When the slave system receives the alignment signal at the time synchronization control unit, the slave system resets the time measured internally, resets the alignment value, and restarts the time measurement. To do. According to the present invention, the synchronization signal can be exchanged at an arbitrary timing by notifying the slave system in advance of the timing for transmitting the alignment signal. For this reason, even if it is difficult to transmit the synchronization signal in the master system or it is difficult to transmit the synchronization signal periodically, time synchronization on the slave system side becomes possible.

  The present invention is a network device comprising a master system that communicates with a time information distribution source to acquire time information, and a slave system that receives time information from the master system and performs time synchronization. The slave system includes a timing generator that transmits a timing signal at a predetermined interval asynchronously with the master system, and the master system provides the slave system with a unit of the time information in addition to the time information. A synchronization information transmitting unit that transmits a synchronization signal that resets a time that is less than or equal to a time and an alignment signal that indicates an alignment value that is less than or equal to the unit time, and when the slave system receives the synchronization signal from the master system, Time information notified from the master system To the alignment value indicated by the alignment signal received from the master system, after the timing signal transmitted from the timing generator has arrived, And a time synchronization control unit to be set.

  According to the present invention, a timing generator that transmits a timing signal to a slave system at a predetermined interval asynchronously with the master system is provided, and the master system resets the time below the unit time of the time information in addition to the time information. A synchronization signal to be transmitted and an alignment value are transmitted. In response, the slave system resets the internally timed time to the received time information, restarts timekeeping, and waits for the arrival of a timing signal transmitted at a predetermined interval from the timing generator. Set the alignment value. For this reason, even if the master system is processing a high-priority interrupt, such as when an alignment signal is sent, the timing generator does not send the alignment signal at a fixed timing regardless of the processing status of the master system. Since transmission becomes possible, it is possible to provide a network device capable of processing with priority given to time synchronization.

  In the present invention, the master system sets the transmission interval of the timing signal to the timing generator before transmitting the time information to the slave system. According to the present invention, the master system can transmit an alignment-related signal at an arbitrary timing to the slave system by controlling the timing signal transmission interval of the timing generator.

  The present invention also provides a time synchronization method in a network device comprising a master system that communicates with a time information distribution source to acquire time information, and a slave system that receives time information from the master system and performs time synchronization. The master system notifies the slave system of the time information with a unit time accuracy that can ignore the influence of the communication delay through a communication path connecting the master system and the slave system. And after the master system notifies the time information, the transmission time provided independently of the communication path connecting the master system and the slave system at the notified time. Resetting time information below unit time, and the slave system, Upon receiving the period signal, and having a a step restarts the timing reconfigure the time instant being clocked by the internal to the notified time information.

  According to the present invention, in the master system, after notifying the time information via the communication path, the time information of the unit time or less is reset via the transmission path provided independently of the communication path at the notified time. The slave system periodically transmits a signal, and at the time when the slave system receives the synchronization signal, it resets the internally timed time to the notified time information and restarts timekeeping. For this reason, it is possible to avoid a time synchronization shift caused by a delay in notifying time information between the master system and the slave system, and the processing status of the master system or the slave system or the master system and the slave system is determined by the synchronization signal. Synchronization signals can be exchanged without depending on the communication status between the two.

  The present invention provides a master system that communicates with a time information distribution source to acquire time information, a slave system that receives time information from the master system and performs time synchronization, the slave system, the master system, Is a time synchronization method in a network device including a timing generator that asynchronously transmits a timing signal at a predetermined interval, wherein the master system sends the time information to the slave system in addition to the time information. A synchronization signal that resets a time that is less than or equal to a unit time, an alignment signal that indicates an alignment value that is less than or equal to the unit time, and an internal clock when the slave system receives the synchronization signal from the master system. To the time information sent from the master system. A step of setting and restarting the timing; and when the slave system receives the timing signal transmitted from the timing generator and receives the time measured internally from the master system, And a step of setting the alignment value to be indicated.

  According to the present invention, in addition to the time information, the master system transmits a synchronization signal for resetting a time equal to or lower than the unit time of the time information and an alignment value, and the slave system that receives this signal internally measures the time. The time is restarted by resetting the current time to the received time information, and the alignment value received from the master system is set after the arrival of the timing signal transmitted at a predetermined interval from the timing generator. For this reason, even if the master system is processing a high-priority interrupt, such as when an alignment signal transmission is awaited, the timing generator does not relate to the processing status of the master system. Since the signal can be transmitted, the time synchronization can be processed with priority.

  According to the present invention, it is possible to provide a network device capable of performing periodic time synchronization without depending on communication delay and communication status between the master system and the slave system, and a time synchronization method in the device. .

It is a block diagram which shows the structure of the network device which concerns on Embodiment 1 of this invention. It is a figure which shows the structure of the communication frame produced | generated by the network device which concerns on Embodiment 1 of this invention. It is the figure which showed the operation | movement of the time synchronization by the network device which concerns on Embodiment 1 of this invention on the time axis. It is a block diagram which shows the structure of the network apparatus which concerns on Embodiment 2 of this invention. It is the operation | movement sequence diagram which showed the operation | movement of the network device which concerns on Embodiment 2 of this invention in time series. It is a block diagram which shows the structure of the application example of the network device which concerns on Embodiment 2 of this invention. It is a figure which shows the example of a connection structure of the conventional star type | mold network system. It is the figure quoted in order to demonstrate the time synchronization method of the conventional network device. It is a figure which shows the structure of the access point by which the master system and slave system which are shown in FIG. 8 are mounted. It is a figure which shows the format of the communication frame for the time synchronization transferred with the conventional network device.

  Hereinafter, an embodiment for carrying out the present invention (hereinafter simply referred to as the present embodiment) will be described in detail with reference to the accompanying drawings.

(Configuration of Embodiment 1)
FIG. 1 is a block diagram illustrating a configuration of a network device 20A according to the first embodiment. According to FIG. 1, the network device 20A communicates with the time server 10 that is a time information distribution source to acquire time information, and receives time information from the master system 21A to perform time synchronization. It consists of a slave system 22A. A feature is that a transmission path 24 for transmitting a synchronization signal from the master system 21A to the slave system 22A is provided in addition to the communication path 23 for performing communication between the master system 21A and the slave system 22A.

  The master system 21A notifies the slave system 22A of the time information transmission unit 211 for notifying the time information with unit time accuracy that can ignore the influence of the communication delay via the communication path 23, and after notifying the time information, A synchronization signal transmission unit 212 that periodically transmits a synchronization signal that resets time information equal to or less than the unit time through the transmission path 24 at the notified time. In addition, the slave system 22A includes a time synchronization control unit 221 that resets the time measured internally to the notified time information when the synchronization signal is received, and restarts the time measurement.

  The time server 10 and the network device 20A (master system 21A) are connected by a network 30 or the like, and the master system 21A distributes time information from the time server 10 using a protocol for time synchronization such as NTP. Shall receive.

(Operation of Embodiment 1)
In the network device 20A shown in FIG. 1, first, the time synchronization described above is performed between the time server 10 and the master system 21A using a communication protocol for time synchronization (step S11). Thereafter, in the master system 21A, the time information transmission unit 211 transmits the communication information having the format shown in FIG. 2A, for example, by serial communication using the communication path 23 to the slave system 22A. Is notified (step S12).

  At this time, the time information to be notified is not notified with accuracy required by the application because a communication delay occurs between the master system 21A and the slave system 22A. For example, it is possible to notify a time with rough accuracy to such an extent that the influence of communication delay can be ignored. Specifically, in an application that requires time accuracy of 1 millisecond, as shown in FIG. 2A, the slave system 22A has a unit of seconds such as “2010/01/01, 12:34:56”. The time is notified. In contrast, in the conventional time synchronization method, notification is made in units of milliseconds requested by the application as shown as “2010/01/01, 12: 34: 56: 789” in FIG.

  Subsequently, the time information transmission unit 211 transmits a synchronization signal to the slave system 22A via the transmission path 24 provided independently of the communication path 23 at the timing specified in advance by the time of the master system 21A. (Step S13). Normally, this signal is generally realized as an interrupt signal for the slave system 22A. However, the master system 21A transmits a signal to the slave system 22A at a desired timing, and the slave system 22A can immediately process the signal. If so, it does not have to be an interrupt.

  In the slave system 22A, at the timing when the time synchronization control unit 221 receives the synchronization signal from the synchronization signal transmission unit 212 of the master system 21A, the time measured by the slave system 22A itself is set to a preset time. Start counting. After performing the time information synchronization process in this way, the master system 21A and the slave system 22A maintain the time using a mechanism implemented in each of the systems 21A and 22A. In general, time keeping is realized by counting clocks mounted in the respective systems 21A and 22A. However, the characteristics vary depending on the clock source used, and even if time synchronization is performed once, a time lag occurs between the master system 21A and the slave system 22A after a while. For this reason, it is necessary to periodically execute synchronization processing.

  FIG. 3A is a diagram showing a time synchronization method in a time sequence between the master system 21A and the slave system 22A. In the figure, the numerical value shown in the time axis direction represents time in ms units. That is, “993” indicates the timing at which the time less than a second becomes 993 ms in each of the systems 21A and 22A. As indicated by the time lag (Δt) in FIG. 3A, in the situation where the slave system 22A is delayed by about 0.3 ms from the master system 21A, the master system 21A has its own time in milliseconds. A time reset signal (R) as a synchronization signal is sent at a timing when becomes zero. The time synchronization control unit 221 of the slave system 22A resets the time in milliseconds to 0 in accordance with the timing of this signal, and restarts counting. In this way, the time lag after the time reset signal (R) is transmitted can be corrected.

  As a time setting method on the slave system 22A side, the time synchronization control unit 221 performs round-up processing in milliseconds when the slave system 22A is behind the master system 21A. Conversely, when the slave system 22A is advanced, a truncation process in milliseconds is performed.

  In FIG. 3A, the synchronization signal transmission unit 212 transmits the time reset signal (R) at a timing of 0 in milliseconds, but the time reset signal when the time of the master system 21A is x milliseconds. If (R) is transmitted and this is known in advance by the slave system 22A, it is not necessary to issue a signal when the millisecond unit is 0. FIG. 2B shows the format of the communication frame transmitted from the synchronization signal transmission unit 212 to the slave system 22A in that case. FIG. 3B shows the format between the master system 21A and the slave system 22A in that case. The time synchronization method is shown on the time axis. This is a case where it is difficult to transmit the time reset signal when the millisecond unit of the time of the master system 21A is 0, or it is difficult to transmit the time reset signal at regular intervals. In accordance with the format shown in FIG. 2 (b) in advance for the master system 21A side, a numerical value in milliseconds that should be set on the slave system 22A side when the next alignment signal is input. It is.

  Specifically, in the communication frame shown in FIG. 2B, when the slave system 22A receives the alignment signal, information indicating that the time in milliseconds is reset to “789 ms (alignment value)”. Is the command indicated. As shown in FIG. 3B, the synchronization signal transmission unit 212 of the master system 21A transmits an alignment signal (Ali) at a timing when the time in milliseconds of the master system 21A becomes 789 ms. Receiving this, the slave system 22A resets the time information counted by the slave system 22A itself by the time synchronization control unit 221 and resets the time in milliseconds to the preset “789 ms”. Resume counting.

  In the above example, an example of a millisecond unit has been dealt with. For example, even in a rougher unit time such as a unit of 10 milliseconds or 100 milliseconds, a finer unit such as 10 microseconds or 100 microseconds. It may be a unit time. In any case, this sequence may be executed with the time synchronization accuracy required between the systems 21 and 22.

(Effect of Embodiment 1)
As described above, according to the network device 20A according to the first embodiment, it is possible to avoid a time synchronization shift caused by a communication delay for notifying time information between the master system 21A and the slave system 22A. it can. Further, the master system 21A transmits a synchronization signal (alignment signal) to the slave system 22A via the transmission path 24 provided independently of the communication path 23, whereby the processing status of the master system 21A and the slave system 22A In addition, it is possible to exchange synchronization information independent of the communication status between the two systems 21A and 22A. Further, by notifying the slave system 22A side of the timing for transmitting the alignment signal in advance, the synchronization signal can be transmitted and received at an arbitrary timing.

(Configuration of Embodiment 2)
In the network device 20A according to the first embodiment described above, a time reset signal and an alignment signal (hereinafter collectively referred to as an alignment signal) are issued by a command. As described above, when the alignment signal is generated by software or when the master system 21A is operating in a non-real-time environment, depending on the internal processing status of the master system 21A at the timing of transmitting the alignment signal, the alignment is performed. Signal transmission may be delayed. For example, the master system 21A is executing a high priority interrupt process. In order to avoid this, a method for preferentially processing alignment signal transmission is required. A mechanism for guaranteeing this will be described below as a second embodiment.

  FIG. 4 is a block diagram illustrating a configuration of the network device 20B according to the second embodiment. According to FIG. 4, the network device 20B communicates with the time server 10 that is a time information distribution source to acquire time information, and receives time information from the master system 21B to perform time synchronization. It consists of a slave system 22B. The difference from the first embodiment shown in FIG. 1 is that a timing generator 25 as an alignment signal source that transmits a timing signal at a predetermined interval asynchronously with the master system 21B is added to the slave system 22B in the above configuration. There is. The difference in configuration from the slave system 22 </ b> A side of the first embodiment shown in FIG. 1 is that a timing generator 25 is connected instead of the transmission path 24.

  The master system 21B transmits to the slave system 22B, in addition to the time information, a synchronization signal that resets a time that is less than the unit time of the time information and / or an alignment signal that indicates an alignment value that is less than the unit time. And a timing signal transmission interval setting unit 214 that sets a timing signal transmission interval to the timing generator 25 before transmitting time information to the slave system 22B. When the slave system 22B receives the synchronization signal from the master system 21B, the slave system 22B resets the time measured internally to the time information notified from the master system 21B, restarts the time measurement, and is transmitted from the timing generator 25. A time synchronization control unit 222 that waits for the arrival of the timing signal and sets the time measured internally to the alignment value indicated by the alignment signal received from the master system 21B.

  As an alignment signal source, the timing generator 25 connected to the outside of the master system 21B and the slave system 22B can be a microprocessor as long as it can send a timing signal for setting an alignment value at a predetermined timing. It may be a separate system or an IC (Integrated Circuit) alone. As a specific example of the timing generator 25, an RTC (Real Time Clock) may be adopted. Usually, such an IC has a function of transmitting a signal at regular intervals, for example, at intervals of 1 second, and this function is used as an alignment signal. When time accuracy is required, an RTC equipped with a highly accurate temperature compensated crystal is used.

(Operation of Embodiment 2)
Hereinafter, the operation of the network device 20B according to the second embodiment shown in FIG. 4 will be described in detail with reference to the operation sequence diagram shown in FIG.

  First, in the master system 21B, information for time synchronization is acquired by communicating with the time server 10 via the network 30 (step S101). Next, in the master system 21B, the timing signal transmission interval setting unit 214 sets a transmission interval of timing signals serving as a trigger for setting an alignment value for the timing generator 25 (step S102). Thereafter, in the master system 21B, the synchronization signal transmission unit 213 transmits time information to the slave system 22B (step S103), and then transmits information related to alignment, such as time reset and alignment values (step S104).

  In the slave system 22B that receives this, the time synchronization control unit 222 sets the internal time to the time notified from the master system 21B by the synchronization signal transmission unit 213, and counts the time while the slave system 22B itself counts the time. Waiting for the arrival of a timing signal for starting alignment from the generator 25 (step S105). In the slave system 22B, the time synchronization control unit 222 resets the time counted internally when the timing signal for starting the alignment arrives from the timing generator 25, and transmits the synchronization signal of the master system 21B. Alignment is performed according to the specified alignment value at the time specified by the unit 213 (step S106).

  Note that the timing signal transmission interval, time information setting, and alignment value setting may be switched in order or may be partially omitted depending on the configuration and characteristics of the installed system. In the network device 20B according to the second embodiment, the timing signal transmission interval is set by the master system 21B (timing signal transmission interval setting unit 214). However, the slave system 22B may set the timing signal transmission interval. The value set in may be used. Furthermore, the timing signal generated by the timing generator 25 that triggers the reset or alignment value is supplied only to the slave system 22B, but by supplying the timing signal to the master system 21B as well, alignment related values can be obtained. It can also be used when making decisions.

(Application example of Embodiment 2)
As a specific implementation example of the network device 20B that performs time synchronization using the timing generator 25 described above, a backbone router 100 of an ISA (International Society of Automation) 100 network illustrated in FIG. 6 will be described as an example.

  Here, the backbone router 100 is equipped with two systems: a backbone network system (BNS101) that performs network processing on the backbone side, and a wireless network system (WNS102) that performs processing on the wireless side, each of which is a separate processor. Operate. The time server exists on the backbone side (not shown), and the operation when the BNS 101 performs time synchronization with this time server and further notifies the WNS 102 of the synchronized time will be described.

  In this application example, the time management unit 110 of the BNS 101 and the time management unit 120 of the WNS 102 included in the backbone router maintain time information using the time count clock sources 130 and 140 mounted in each. However, in a general system, the time count clock sources 130 and 140 often do not have sufficient accuracy with respect to application requirements, and in this case, the time count clock sources 130 and 140 cannot keep time with the required accuracy. For this reason, apart from the time sound clock sources 130 and 140 possessed by the systems 101 and 102, a high-accuracy clock source 103 having an accuracy satisfying the application requirements is mounted on the backbone router, and the interval set by the BNS 101 is fixed. The time tick is supplied to each of the systems 101 and 102. This time tick supply is simultaneously notified to the systems 101 and 102 (tick supply).

  The time tick is connected to each of the external clock interrupt management units 112 and 122 included in the time management units 110 and 120 of the systems 101 and 102, and the processors of the systems 191 and 102 have internal time at this tick timing. The time information held by the holding units 111 and 121 is aligned. For example, when time ticks are set at intervals of 1 second, time information is aligned every second. In the following, an operation will be described when time ticks are supplied at 1 second intervals and the WNS 102 synchronizes time with an accuracy of 1 millisecond.

  The BNS 101 synchronized with the time server sets the synchronized time information in the time holding unit 111 of the time management unit 110 and records the time with millisecond accuracy based on the clock supplied from the time count clock source 130. Thereafter, the time information held by the time holding unit 111 is captured in milliseconds at the timing when the tick is input from the high-accuracy clock source 103. Here, it is obtained by hardware using a timer capture function generally installed in a microcomputer or the like.

  Next, the BNS 101 notifies the WNS 102 of the time in milliseconds of the captured time information as “offset information”. For example, when the time when the tick is captured at the BNS 101 side is 12: 34: 56.789, the WNS 102 is notified of 789 ms as offset information. Before or after this operation, it is necessary to separately notify time information in units of seconds, here, 12:34:56 information.

  The WNS 102 that has received this information can synchronize the time with the BNS 101 in milliseconds by realigning the time in milliseconds of the time information held by its time management unit 120 to 789 ms at the timing of receiving the tick. it can. This operation follows the time sequence diagram shown in FIG.

  In the application example described above, the time information is synchronized in milliseconds. However, the accuracy according to the time accuracy that can be stored by the application request and the time management function can be realized by the same mechanism. Although the method of time synchronization related to synchronization between two systems (BNS 101 and WNS 102) has been described here, the same method can be used for time synchronization of three or more systems by increasing the tick signal supply destination from the high-precision clock source 103. It is feasible.

(Effect of Embodiment 2)
As described above, the network device 20B according to the second embodiment includes the timing generator 25 that transmits a timing signal to the slave system 22B at a predetermined interval asynchronously with the master system 21B. In addition to the time information, a synchronization signal for resetting a time equal to or less than the unit time of the time information and an alignment value are transmitted. In response to this, the slave system 22B resets the internally timed time to the received time information, restarts timekeeping, and waits for the arrival of a timing signal transmitted from the timing generator 25 at a predetermined interval. Set the received alignment value.

  For this reason, even when the transmission of the alignment signal is awaited, for example, when the master system 21B is processing a high priority interrupt, the timing generator 25 causes the constant timing regardless of the processing status of the master system 21B. Thus, it is possible to provide the network device 20B capable of processing with priority given to time synchronization.

  In the first and second embodiments, the slave system 22A (22B) that cannot be directly synchronized with the time server 10 is time-synchronized with a desired accuracy via the master system 21A (21B). In such a network where time synchronization is required, for example, an access point as a wireless network device that has received time information from an upper network provides an internal architecture of the access point for distributing the information to the wireless device. To do. Specifically, the focus is on time synchronization between a master system and a slave system constituting the access point, and the presence or absence of the time server 10 is irrelevant. However, in actual applications, there are many cases where a role such as the time server 10 is required, and a configuration in which the function is included in the master system 21A (21B) even if it does not exist is conceivable. In the present embodiment, the existence of the time server 10 is shown in all cases.

  The network devices 20A and 20B according to the present embodiment can be applied to all systems that perform communication in accordance with the TDMA method. For example, the present invention can be applied in a similar manner to a system in which each communication node is synchronized and communicated with a time reference arranged on a network.

(Time synchronization method for network devices)
The time synchronization method in the network device according to the first embodiment of the present invention includes, for example, a master system 21A that acquires time information by communicating with a time information distribution source in FIG. 1, and time information from the master system 21A. Is a time synchronization method in the network device 20A including the slave system 22A that performs time synchronization in response to the provision of. Then, the master system 21A has the unit time accuracy with respect to the slave system 22A with negligible influence of the communication delay through the communication path 23 connecting the master system 21A and the slave system 22A. Informing the information (S12), and after the master system 21A notifies the time information, it is independent of the communication path 23 connecting the master system 21A and the slave system 22A at the notified time. Step (S13) of periodically resetting the time information below the unit time via the transmission path 24 provided, and when the slave system 22A receives the synchronization signal, the time is internally measured. Resetting the time to the notified time information and restarting the timing. Is shall.

  According to the time synchronization method in the network device according to the first embodiment, in the master system 21A, after notifying the time information via the communication path 23, the transmission path provided independently of the communication path 23 at the notified time. 24, a synchronization signal for resetting time information below the unit time is periodically transmitted, and the slave system 22A sets the internally timed time to the notified time information when the synchronization signal is received. Then restart timing. For this reason, it is possible to avoid a time synchronization shift caused by a delay for notifying the time information between the master system 21A and the slave system 22A, and the processing status of the master system 21A and the slave system 22A or the master by the synchronization signal. Synchronization signals can be exchanged without depending on the communication status between the system 21A and the slave system 22A.

  In addition, the time synchronization method in the network device according to the second embodiment includes, for example, a master system 21B that obtains time information by communicating with a time information distribution source in FIG. 4, and provides time information from the master system 21B. Time synchronization method in a network device 20B comprising: a slave system 22B that performs time synchronization in response to the reception, and a timing generator 25 that transmits a timing signal to the slave system 22B at a predetermined interval asynchronously with the master system 21B. It is. For example, in FIG. 5, the master system 21B, with respect to the slave system 22B, in addition to the time information, a synchronization signal that resets a time that is less than the unit time of the time information, and an alignment that is less than the unit time A step of transmitting an alignment signal indicating a value (S103, S104), and when the slave system 22B receives the synchronization signal from the master system 21B, the time measured internally is transmitted from the master system 21A. Resetting the time information to the time information and restarting the time measurement (S105), the slave system 22B waits for the arrival of the timing signal transmitted from the timing generator 25, and sets the time measured internally. The alignment signal received from the master system 21B A step (S106) for setting the alignment values shown, and has a.

  According to the time synchronization method in the network device according to the second embodiment, the master system 21B transmits, in addition to the time information, a synchronization signal that resets a time equal to or less than the unit time of the time information and an alignment value. The received slave system 22B resets the internally timed time to the received time information and restarts the timekeeping. The master system 21B waits for the arrival of a timing signal transmitted from the timing generator 25 at a predetermined interval. Set the alignment value received from. For this reason, even when the transmission of the alignment signal is awaited, such as when the master system 21B is processing a high-priority interrupt, the timing generator 25 does not depend on the processing status of the master system 21A at a constant timing. Since alignment-related signals can be transmitted, time synchronization can be prioritized for processing.

  As described above, according to the network device and the time synchronization method using the device of the present invention, it is possible to perform periodic time synchronization without depending on the communication delay and communication status between the master system and the slave system. To do. According to the present invention, since it can be realized only by minor hardware modification and corresponding software implementation, it can be applied to many network devices adopting the conventional method. The hardware implementation cost is almost the same as the conventional method.

  As mentioned above, although this embodiment was described, it cannot be overemphasized that the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above embodiment. Further, it is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

  10. Time server, 20A (20B) Network equipment, 21A (21B) Master system, 22A (22B) Slave system, 23 Communication path, 24 Transmission path, 25 Timing generator , 30 ··· network, 100 ··· backbone router, 101 ··· backbone network system (BNS), 102 ··· wireless network system (WNS), 103 high precision clock source, 110, 120 ··· time management unit, 111, 121 ..Time holding unit, 112, 122 ..External clock interrupt management unit, 130, 140 ..Time count clock source, 211 ..Time information transmission unit, 212, 213 ..Synchronous signal transmission unit, 214. Sending interval setting unit, 221, 222 ..Time synchronization control unit

Claims (8)

A network device composed of a master system that communicates with a time information distribution source to acquire time information, and a slave system that receives time information from the master system and performs time synchronization,
Apart from a communication path for performing communication between the master system and the slave system, a transmission path for transmitting a synchronization signal from the master system to the slave system is provided,
The master system notifies the slave system of the time information with a unit time accuracy determined in advance via the communication path, and notifies the time after the time information is notified. A synchronization signal transmitting unit that transmits the synchronization signal that resets time information equal to or less than the unit time via the transmission path, and
The slave system is
A network device, comprising: a time synchronization control unit that resets the time measured internally to the notified time information when the synchronization signal is received, and restarts the time measurement. The accuracy of the unit time is
2. The network device according to claim 1, wherein the influence of the communication delay can be ignored. The slave system is
In the time synchronization control unit, when there is a delay in the time of the slave system compared to the time of the master system, the time information of the unit time or less is rounded up, and the slave system is compared with the master system. 2. The network device according to claim 1, wherein when time advances, the time information below the unit time is rounded down. The master system is
In the synchronization signal transmission unit, after transmitting the next synchronization signal through the transmission path, transmits an alignment signal indicating an alignment value of the unit time or less to be set in the slave system,
The slave system is
2. The network device according to claim 1, wherein when the alignment signal is received by the time synchronization control unit, the time currently measured internally is reset, reset to the alignment value, and time measurement is resumed. A network device composed of a master system that communicates with a time information distribution source to acquire time information, and a slave system that receives time information from the master system and performs time synchronization,
A timing generator that transmits a timing signal at a predetermined interval asynchronously with the master system to the slave system,
The master system transmits to the slave system, in addition to the time information, a synchronization signal that resets a time that is less than or equal to the unit time of the time information, or synchronization information that indicates an alignment value that is less than or equal to the unit time. With a transmitter,
When the slave system receives the synchronization signal from the master system, the slave system resets the time measured internally to the time information notified from the master system, and restarts the time measurement, and is transmitted from the timing generator. A network device comprising: a time synchronization control unit that waits for the arrival of the timing signal and sets the time measured internally to an alignment value indicated by the alignment signal received from the master system. The master system is
6. The network device according to claim 5, wherein a transmission interval of the timing signal is set for the timing generator before transmitting the time information to the slave system. A time synchronization method in a network device comprising a master system that communicates with a time information distribution source to acquire time information and a slave system that receives time information from the master system and performs time synchronization,
The master system is
Notifying the slave system of the time information with a unit time accuracy that can ignore the influence of the communication delay through a communication path connecting the master system and the slave system;
The master system is
After notifying the time information, the time information equal to or less than the unit time is reset at the notified time via a transmission path provided independently of the communication path connecting the master system and the slave system. Steps,
The slave system is
At the time of receiving the synchronization signal, resetting the time being measured internally to the notified time information, and restarting the time measurement,
A time synchronization method in a network device, comprising: A master system that communicates with a time information distribution source to acquire time information, a slave system that receives time information from the master system and performs time synchronization, and the slave system is asynchronous with the master system. A timing generator for transmitting a timing signal at intervals of a time synchronization method in a network device comprising:
The master system is
To the slave system, in addition to the time information, transmitting a synchronization signal for resetting a time equal to or less than the unit time of the time information, and an alignment signal indicating an alignment value equal to or less than the unit time;
The slave system is
When receiving the synchronization signal from the master system, resetting the time that is internally timed to time information transmitted from the master system,
The slave system is
Waiting for the arrival of the timing signal transmitted from the timing generator, and setting the time measured internally to an alignment value indicated by the alignment signal received from the master system;
A time synchronization method in a network device, comprising:

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