30 is realized by a wired communication circuit or the like corresponding to a communication standard such as a wired local area network (LAN).

When determiner 40 determines that at least one of the number of incrementation times of the third count value and the number of incrementation times of the fourth count value within the update cycle of the second count value is not normal, slave transmitter 30 transmits a transmission request for the first count value to master device 12.

Slave receiver 32 is a receiver for slave device 14 to receive various types of information from master device 12. For example, slave receiver 32 receives the timing information transmitted from master transmitter 18. For example, slave receiver 32 is realized by a communication circuit or the like. Specifically, for example, slave receiver 32 is realized by a wired communication circuit or the like corresponding to a communication standard such as a wired local area network (LAN).

Slave storage 34 is a storage device that stores information necessary for the information processing, the computer program, and the like. For example, slave storage 34 is realized by a semiconductor memory or the like.

FIG. 4 is a flowchart illustrating an example of an operation of master device 12 of communication system 10 in FIG. 1. An example of the operation of master device 12 of communication system 10 will be described with reference to FIG. 4.

As illustrated in FIG. 4, when wired communication with slave device 14 is established, master device 12 initializes first counter 24 and second counter 26 (step S1). For example, master device 12 initializes first counter 24 by setting the first count value to 0, and initializes second counter 26 by setting the second count value to 0.

Upon initializing first counter 24 and second counter 26, master device 12 transmits a first time stamp command (step S2). For example, the time stamp command is a command in which the first count value is written, and master device 12 transmits the command in which the first count value is written. Here, the first count value is 0. Furthermore, for example, master device 12 also writes the second count value in the first time stamp command. Here, the second count value is 1. That is, the second count value of second counter 26 is updated from 0 to 1 at the timing of transmitting the first time stamp command.

When transmitting the first time stamp command, master device 12 determines whether or not the timing is an update timing to update the first count value (step S3).

For example, master device 12 starts incrementing the first count value from the time at which the first time stamp command is transmitted, and determines that the timing is an update timing of the first count value when the first unit time has elapsed from the time at which the first time stamp command is transmitted. Furthermore, for example, when the first count value has been updated, master device 12 determines that the timing is an update timing of the first count value when the first unit time has elapsed from the time at which the first count value was updated immediately before.

On the other hand, for example, when the first unit time has not elapsed from the time at which the first time stamp command is transmitted, master device 12 determines that the timing is not an update timing of the first count value. Furthermore, for example, when the first count value has been updated, master device 12 determines that the timing is not an update timing of the first count value when the first unit time has not elapsed from the time at which the first count value was updated immediately before.

When the timing is an update timing of the first count value (Yes in step S3), master device 12 increments the first count value (step S4).

When the timing is not an update timing of the first count value (No in step S3) and when the first count value has been incremented (step S4), master device 12 determines whether or not the timing is an update timing of the second count value (step S5).

For example, master device 12 starts updating the second count value from the time at which the first time stamp command is transmitted, and determines that the timing is an update timing of the second count value when the second unit time has elapsed from the time at which the first time stamp command is transmitted. Furthermore, for example, when the second count value has been updated, master device 12 determines that the timing is an update timing of the second count value when the second unit time has elapsed from the time at which the second count value was updated immediately before.

On the other hand, for example, when the second unit time has not elapsed from the time at which the first time stamp command is transmitted, master device 12 determines that the timing is not an update timing of the second count value. Furthermore, for example, when the second count value has been updated, master device 12 determines that the timing is not an update timing of the second count value when the second unit time has not elapsed from the time at which the second count value was updated immediately before.

When the timing is an update timing of the second count value (Yes in step S5), master device 12 updates the second count value (step S6). For example, master device 12 updates the second count value from 0 to 1 when the second count value is 0, and updates the second count value from 1 to 0 when the second count value is 1.

When the timing is not an update timing of the second count value (No in step S5) and when the second count value has been updated (step S6), master device 12 determines whether or not a transmission request for the first count value has been received (step S7). Specifically, for example, master device 12 determines whether or not the transmission request is received from the plurality of slave devices 14.

When the transmission request of the first count value is not received (No in step S7), master device 12 transmits other commands to each of the plurality of slave devices 14 (step S8), and determines again whether or not the timing is an update timing of the first count value (step S3). For example, master device 12 transmits a command in which the second count value is written.

When the transmission request of the first count value is received (Yes in step S7), master device 12 transmits a time stamp command in which the first count value is written (step S9), and determines again whether or not the timing is an update timing of the first count value (step S3). For example, master device 12 transmits the first count value to slave device 14 that is the transmission source of the received transmission request among the plurality of slave devices 14, that is, slave device 14 that has transmitted the transmission request.

FIG. 5 and FIG. 6 are flowcharts illustrating an example of an operation of slave device 14 of communication system 10 in FIG. 1. FIG. 7 and FIG. 8 are views for explaining an example of an operation of slave device 14 of communication system 10 in FIG. 1. An example of the operation of slave device 14 of communication system 10 will be described with reference to FIGS. 5 to 8. Note that, in the following description, an example of the operation of one slave device 14 among the plurality of slave devices 14 will be described, but since the other slave devices 14 also perform similar operations, details of the description of the example of the operation of the other slave device 14 will be omitted.

As illustrated in FIG. 5, when wired communication with master device 12 is established, slave device 14 receives a first time stamp command (step S11). For example, slave device 14 receives a command in which the first count value and the second count value are written. Here, the first count value is 0, and the second count value is 1.

Upon receiving the first time stamp command, slave device 14 initializes third counter 36 and fourth counter 38 (step S12). For example, slave device 14 initializes third counter 36 by setting the third count value to 0, and initializes fourth counter 38 by setting the fourth count value to 0.

After initializing third counter 36 and fourth counter 38, slave device 14 determines whether or not the timing is an update timing to update the fourth count value (step S13).

For example, slave device 14 starts incrementing the fourth count value from the time at which the first time stamp command is received, and determines that the timing is an update timing of the fourth count value when the third unit time has elapsed from the time at which the first time stamp command is received. Furthermore, for example, when the fourth count value has been updated, slave device 14 determines that the timing is an update timing of the fourth count value when the third unit time has elapsed from the time at which the fourth count value was updated immediately before.

On the other hand, for example, when the third unit time has not elapsed from the time at which the first time stamp command is received, slave device 14 determines that the timing is not an update timing of the fourth count value. Furthermore, for example, when the fourth count value has been updated, slave device 14 determines that the timing is not an update timing of the fourth count value when the third unit time has not elapsed from the time at which the fourth count value was updated immediately before.

When the timing is an update timing of the fourth count value (Yes in step S13), slave device 14 updates the fourth count value (step S14). Here, the fourth count value is incremented.

When the timing is not an update timing of the fourth count value (No in step S13) and when the fourth count value has been incremented (step S14), slave device 14 determines whether or not the timing is an update timing of the third count value (step S15).

For example, slave device 14 starts incrementing the third count value from the time at which the first time stamp command is received, and determines that the timing is an update timing of the third count value when the first unit time has elapsed from the time at which the first time stamp command is received. Furthermore, for example, when the third count value has been updated, slave device 14 determines that the timing is an update timing of the third count value when the first unit time has elapsed from the time at which the third count value was updated immediately before.

On the other hand, for example, when the first unit time has not elapsed from the time at which the first time stamp command is received, slave device 14 determines that the timing is not an update timing of the third count value. Furthermore, for example, when the third count value has been updated, slave device 14 determines that the timing is not an update timing of the third count value when the first unit time has not elapsed from the time at which the third count value was updated immediately before.

When the timing is an update timing of the third count value (Yes in step S15), slave device 14 updates the third count value (step S16), and resets the fourth count value (step S17). For example, slave device 14 increments the third count value from 0 to 1, and resets the fourth count value to 0.

When the timing is not an update timing of the third count value (No in step S15) and when the fourth count value is reset (step S17), slave device 14 determines whether a time stamp command has been received (step S18). For example, slave device 14 periodically receives a command from master device 12, determines that the time stamp command has been received when the command received from master device 12 is a time stamp command, and determines that the time stamp command has not been received when the command received from master device 12 is not a time stamp command. Here, the time stamp command is a command in which the first count value is written.

When the time stamp command has not been received (No in step S18), slave device 14 determines whether or not the second count value has been updated (step S19). As described above, for example, slave device 14 receives the timing information from master device 12, and determines whether or not the second count value has been updated based on the timing information.

For example, slave device 14 periodically receives a command from master device 12, and the second count value is written in the command. That is, for example, slave device 14 periodically receives the second count value. When the second count value received this time has not been updated from the second count value received last time, slave device 14 determines that the second count value has not been updated. Meanwhile, when the second count value received this time has been updated from the second count value received last time, slave device 14 determines that the second count value has been updated.

When the second count value has not been updated (No in step S19), slave device 14 determines again whether or not the timing is an update timing of the fourth count value (step S13).

When the second count value is updated (Yes in step S19), slave device 14 determines whether or not the number of incrementation times of the third count value within the update cycle of the second count value is normal (step S20). For example, slave device 14 sets the time from the timing at which the second count value is updated last time to the timing at which the second count value is updated this time as the update cycle of the second count value. Then, slave device 14 determines that the number of incrementation times of the third count value within the update cycle is normal when the number of incrementation times of the third count value within the update cycle is the same as the quotient of (second unit time/first unit time), and determines that the number of incrementation times of the third count value within the update cycle is not normal when the number of incrementation times of the third count value within the update cycle is not the same as the quotient of (second unit time/first unit time).

For example, as illustrated in FIG. 7, when (second unit time/first unit time)=2, slave device 14 determines that the number of incrementation times of the third count value within the update cycle is normal when the number of incrementation times of the third count value is 2, and determines that the number of incrementation times of the third count value within the update cycle is not normal when the number of incrementation times of the third count value is not 2.

When the number of incrementation times of the third count value within the update cycle of the second count value is normal (Yes in step S20), slave device 14 determines again whether or not the timing is an update timing of the fourth count value (step S13).

When the number of incrementation times of the third count value within the update cycle of the second count value is not normal (No in step S20), slave device 14 generates an alarm (step S21), transmits a transmission request of the first count value to master device 12 (step S22), and determines again whether or not the timing is an update timing of the fourth count value (step S13).

Slave device 14 determines whether or not a time stamp command has been received (step S18), and when the time stamp command has been received (Yes in step S18), determines whether or not the third count value is different from the first count value written in the time stamp command (step S23).

When the third count value is not different from the first count value written in the time stamp command (No in step S23), slave device 14 determines whether or not the second count value has been updated (step S19).

When the third count value is different from the first count value written in the time stamp command (Yes in step S23), slave device 14 generates an alarm (step S24) and corrects the third count value (step S25).

For example, as shown in FIG. 8, when the third count value is 2 and the first count value written in the time stamp command is 3, slave device 14 generates an alarm and corrects the third count value from 2 to 3.

Communication system 10 according to the first exemplary embodiment has been described above.

Communication system 10 according to the first exemplary embodiment includes master device 12 and one or more slave devices 14 that communicate with master device 12. Master device 12 includes: first counter 24 that increments the first count value every time the first unit time elapses; second counter 26 that updates the second count value every time the second unit time elapses; and master transmitter 18 that transmits timing information indicating a timing at which the second count value is updated to each of one or more slave devices 14. Each of one or more slave devices 14 includes: third counter 36 that increments the third count value every time the first unit time elapses; fourth counter 38 that increments the fourth count value every time the third unit time shorter than the first unit time elapses, and resets the fourth count value at a timing at which third counter 36 increments the third count value; and slave receiver 32 that receives the timing information transmitted from master transmitter 18.

According to this, by transmitting not the time information but the timing information indicating the timing at which the second count value is updated to each of one or more slave devices 14, it is possible to suppress deviation of the time information of master device 12 and the time information of slave device 14 while curbing increase in the bandwidth used in a network. The reason why the increase in the bandwidth used in a network can be curbed is that the second count value is one-bit information of 0/1 and is smaller than the data amount related to the time information. In particular, in the notification from master device 12 to slave device 14 in units of nanoseconds, the effect of suppressing the bandwidth used in a network becomes remarkable.

Furthermore, in communication system 10 according to the first exemplary embodiment, each of one or more slave devices 14 further includes determiner 40 and slave transmitter 30. Determiner 40 determines whether or not at least one of the number of incrementation times of the third count value and the number of incrementation times of the fourth count value within the update cycle of the second count value is normal based on the timing information received by slave receiver 32 of slave device 14. When determiner 40 determines that at least one of the number of incrementation times of the third count value and the number of incrementation times of the fourth count value within the update cycle is not normal, slave transmitter 30 transmits a transmission request for the first count value to master device 12. Master device 12 further includes master receiver 20 that receives the transmission request transmitted from slave transmitter 30 of each of one or more slave devices 14. Master transmitter 18 transmits the first count value to slave device 14 that is the transmission source of the transmission request received by master receiver 20 among one or more of slave devices 14.

According to this, transmission and reception of the first count value can be performed only when at least one of the number of incrementation times of the third count value and the number of incrementation times of the fourth count value within the update cycle of the second count value is not normal. Therefore, it is possible to suppress deviation of the time information held by master device 12 and the time information held by slave device 14 while curbing increase in the bandwidth used in a network.

Furthermore, in communication system 10 according to the first exemplary embodiment, the second unit time is an integer multiple of the first unit time.

Accordingly, it is possible to easily determine whether or not the number of incrementation times of the third count value within the update cycle of the second count value is normal.

Furthermore, in communication system 10 according to the first exemplary embodiment, the second unit time is an integer multiple of the third unit time.

Accordingly, it is possible to easily determine whether or not the number of incrementation times of the fourth count value within the update cycle of the second count value is normal.

Furthermore, in communication system 10 according to the first exemplary embodiment, the third unit time is 1/integer times the first unit time.

Accordingly, it becomes easy to ascertain the time information based on the third count value and the fourth count value.

Second Exemplary Embodiment

FIG. 9 is a flowchart illustrating an example of an operation of the slave device of the communication system according to a second exemplary embodiment. FIG. 10 is a view for explaining an example of an operation of the slave device of the communication system in FIG. 9. A communication system according to the second exemplary embodiment will be described with reference to