JP2010101793A - Time synchronization system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve accurate time synchronization by using only a signal wire of existing serial communications among a plurality of CPUs. <P>SOLUTION: In a time synchronization system for synchronizing time between a transmission-side CPU and a reception-side CPU, the transmission-side CPU transmits both a report signal for reporting the transmission of time according to a prescribed transmission timing and a report signal transmission time T+n/N, and the reception-side CPU performs a time calibration to the time obtained by adding both the time q required for the transmission of the report signal from the transmission-side CPU to the reception-side CPU and the elapsed time p+m<SB>2</SB>/M-m<SB>1</SB>/M from a report signal reception time T'+m<SB>1</SB>/M to the execution of the time calibration to the report signal transmission time. The transmission-side CPM transmits an interval signal at prescribed intervals. The reception-side CPM receives the interval signal, determines the number of clock pulses per interval, and performs interval calibrations to alter an interval setting value M. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a time synchronization system that synchronizes time among a plurality of CPUs.

  The surveying instrument includes a plurality of slave CPUs such as an angle measuring CPU for performing angle measurement and a distance measuring CPU for performing distance measurement, and a master CPU (main CPU) for managing and controlling these slave CPUs. It has been. (See Non-Patent Document 1 below).

Generally, a CPU has a built-in clock (crystal oscillator), and clock pulses are output from the clock at an accurate cycle. For this reason, the CPU can always know the current time or the elapsed time from a certain time point by always counting the clock pulses (hereinafter referred to as clock count). When a plurality of CPUs are used, there is an error in each clock, so it is necessary to set the time periodically among the plurality of CPUs, that is, to synchronize the time. However, in the case of a surveying instrument, accurate time synchronization has not been achieved among a plurality of CPUs.
Japan Surveying Instruments Manufacturers Association, latest surveying instrument manual, Sankaido, July 29, 2003, p. 128

  However, recently, a surveying instrument that accurately measures the distance and angle to the target while tracking the moving target has been required. In order to accurately measure the distance and angle to the target while tracking the moving target, it is necessary that the time is accurately synchronized between the angle measurement CPU and the distance measurement CPU. This can be easily solved by connecting a signal line for synchronization based on the clock of the master CPU from the master CPU to the CPU for angle measurement and the CPU for distance measurement. However, in this case, when there are many CPUs built in the surveying instrument, there is a problem that the number of signal lines increases and the apparatus becomes large.

  The present invention has been made in view of the above problems, and an object of the present invention is to achieve highly accurate time synchronization among a plurality of CPUs using only existing serial communication signal lines.

In order to solve the above-mentioned problem, in the invention according to claim 1, in the time synchronization system in which the time is synchronized between the transmission side CPU and the reception side CPU,
The transmission-side CPU includes notification signal transmission means for transmitting a notification signal for notification of current time transmission according to a predetermined transmission timing, notification signal transmission time acquisition means for acquiring the transmission time of the notification signal, and notification signal transmission time. A notification signal transmission time transmission means for transmitting,
The receiving CPU includes a notification signal receiving unit that receives a notification signal, a notification signal reception time acquisition unit that acquires a time when the notification signal is received, a notification signal transmission time reception unit that receives a notification signal transmission time, and a notification Time calibrating means for calibrating the time to a time obtained by adding the time required for the notification signal to be transmitted from the transmitting CPU to the receiving CPU at the signal transmission time and the elapsed time from the notification signal receiving time to the time calibration execution is provided. It is characterized by that.

  According to a second aspect of the present invention, in the first aspect of the invention, the transmission timing is initially set to be a short time interval and gradually longer, and after a predetermined time, the transmission timing is a constant time interval. And

  In the invention according to claim 3, in the invention according to claim 1 or 2, when the notification signal is received a plurality of times, or the time for performing the time calibration has passed a predetermined time or more from the reception time of the notification signal. In this case, the time calibration is not performed.

In the invention according to claim 4, in the invention according to claim 1, 2, or 3,
The transmitting CPU includes interval signal transmitting means for transmitting an interval signal at a predetermined interval,
The receiving CPU calculates the number of clock pulses per interval from interval signal reception time acquisition means for acquiring the time at which the interval signal is received, and the current interval signal reception time and the previous interval signal reception time. It is characterized by comprising clock counting means and interval calibration means for calibrating the interval setting value set in the receiving CPU so that the intervals coincide between the transmitting CPU and the receiving CPU.

  In the invention according to claim 5, in the invention according to claim 4, the number of clock pulses per interval is calculated from the time when the previous interval signal was received and the time when the current interval signal was received. However, the interval calibration is performed if it is within ± 1% of the number of clock pulses per interval calculated from the clock frequency.

  The invention according to claim 6 is the invention according to claim 4 or 5, wherein the interval calibration is performed by using an average value of the number of clock pulses per interval in a predetermined number of intervals. .

  In the invention according to claim 7, in the invention according to claim 6, the interval calibration is performed with an average value of the number of clock pulses per interval obtained until the predetermined number of intervals is reached. Then, after reaching the predetermined number of intervals, the interval setting value of the receiving CPU is compared with the average value of the number of clock pulses per interval in the predetermined number of intervals, and the interval setting value is set to +1 or It is characterized by increasing or decreasing by -1.

  According to the first aspect of the present invention, in the time synchronization system in which the time is synchronized between the transmission side CPU and the reception side CPU, the transmission side CPU transmits a notification signal that notifies the current time transmission according to a predetermined transmission timing. A notification signal transmission unit; a notification signal transmission time acquisition unit configured to acquire a transmission time of the notification signal; and a notification signal transmission time transmission unit configured to transmit the notification signal transmission time. The receiving CPU receives the notification signal. Notification signal receiving means, notification signal reception time acquiring means for acquiring the time when the notification signal was received, notification signal transmission time receiving means for receiving the notification signal transmission time, and the notification signal from the transmitting CPU at the notification signal transmission time Time calibration that calibrates the time to the time required for transmission to the receiving CPU and the elapsed time from the notification signal reception time to the time calibration execution Because and a stage, can time calibrated to match the transmitting-side CPU to the reception-side CPU at a predetermined timing, can be maintained in the CPU is always time synchronization. In addition, at the time of time calibration, the time calibration is performed by adding the time required for the notification signal to be transmitted from the transmission CPU to the reception CPU at the notification signal transmission time and the elapsed time from the notification signal reception time to the time calibration execution. Thus, the time synchronization error can be minimized.

  According to the second aspect of the present invention, the transmission timing for performing time calibration is initially set to be gradually longer at short time intervals, so that the receiving CPU is in a short time from a state where time synchronization is not achieved. You can move to a time-synchronized state. Since the transmission timing is set to a constant time interval after a predetermined time, the time synchronization is regularly taken, and the time synchronization of each CPU is less lost.

  According to the third aspect of the invention, when the notification signal is received a plurality of times, or when the time for performing the time calibration has passed a predetermined time or more from the notification signal reception time, the time calibration is not performed. It is possible to avoid erroneous time synchronization and time synchronization with a large error.

  According to the fourth aspect of the present invention, the transmission side CPU includes interval signal transmission means for transmitting an interval signal at a predetermined interval, and the reception side CPU acquires the time at which the interval signal is received. An acquisition means; a clock count means for calculating the number of clock pulses per interval from the current interval signal reception time and the previous interval signal reception time; and an interval set value set in the reception CPU. And the receiving CPU are equipped with interval calibration means for calibrating so that the intervals coincide with each other. Once the time is calibrated, the time progress between the CPUs becomes the same, and the time calibration interval can be extended. Become.

  According to the invention of claim 5, the number of clock pulses per interval is calculated from the time when the previous interval signal is received and the time when the current interval signal is received, and the number of clock pulses is calculated from the frequency of the clock. Since the interval calibration is performed when the calculated number of clock pulses per interval is within ± 1%, the interval signal is not transmitted or the count value of the number of clock pulses that is clearly incorrect is displayed. When obtained, interval calibration can be prevented.

  According to the invention of claim 6, since the interval calibration is performed using the average value of the number of clock pulses per interval in a predetermined number of intervals, the interval calibration can be performed with higher accuracy.

  According to the invention of claim 7, the interval calibration is performed with the average value of the number of clock pulses per interval obtained so far until the predetermined number of intervals is reached, and reaches the predetermined number of intervals. After that, the interval setting value of the receiving CPU is compared with the average value of the number of clock pulses per interval in the predetermined number of intervals, and the interval setting value is increased or decreased by +1 or −1. The time can be synchronized with, and after that, highly accurate interval calibration can be performed.

  The present invention relates to a time synchronization system that synchronizes time between a master CPU (main CPU) provided in a surveying instrument or the like and a slave CPU such as an angle measuring CPU or a distance measuring CPU, or between slave CPUs. .

  As an example of this time synchronization system, consider time synchronization between two slave CPUs for the sake of simplicity. One transmitting CPU is assumed to periodically execute interval (time interval) calibration and time calibration described later. Hereinafter, such a state is described as a good status, and a state where the status is not good is described as a status failure. The other receiving CPU is assumed to have a status failure. When the status of the transmitting CPU is good, interval calibration and time calibration of the receiving CPU are performed. Since the master CPU always treats the status as good, it always transmits the interval and time.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart of the interval calibration program of the present invention. FIG. 2 is a diagram for explaining an interval calibration method. FIG. 3 is a flowchart of the time calibration program of the present invention. FIG. 4 is a diagram for explaining a time calibration method.

  First, interval calibration will be described. When the interval calibration program is started by the two CPUs, as shown in FIG. 1, the transmission side CPU proceeds to step S11 and describes the count value of the clock pulses of the transmission side CPU (hereinafter referred to as clock count value). ) To determine whether a predetermined interval (for example, 1 ms) has elapsed. If the predetermined interval has not been reached, the process returns to step S11. When the predetermined interval is reached, the process proceeds to step S12, an interval signal is transmitted from the transmission side CPU to the reception side CPU, and the process returns to step S11.

Thereafter, the transmitting CPU repeats steps S11 to S12, and counts N clock pulses from the first time T ₁ of an interval, that is, when the clock count value is 0, as shown in FIG. when it is time T _2, it resets the clock count value to 0, by issuing the interval signal and transmits the interval signal at predetermined intervals. Note that the interval signal does not necessarily have to be output when the clock count value is 0, and may be output when the clock count value is a predetermined value other than 0.

  This interval signal is transmitted only when the transmitting CPU has a good status, no signal is transmitted from the transmitting CPU, and the interval signal can be transmitted immediately. When the interval signal cannot be immediately transmitted due to other interrupt processing or the like, the interval signal is not transmitted.

  On the other hand, when starting the interval calibration program, the receiving CPU proceeds to step S21 and checks whether or not an interval signal has been received. If no interval signal has been received, the process returns to step S21. If an interval signal has been received, the process immediately proceeds to step S22, and the current time, that is, the interval signal reception time is obtained from the clock count value of the receiving CPU.

  Next, proceeding to step S23, the number of clock pulses per interval is calculated from the difference between the time when the previous interval signal was received and the time when the current interval signal was received. Next, proceeding to step S24, if the number of clock pulses per interval calculated in step S23 is within ± 1% of the number of clock pulses per interval calculated from the clock frequency, the transmitting CPU And the receiving CPU are calibrated so that the intervals coincide with each other.

The interval calibration of the receiving CPU will be described in more detail based on FIG. The receiving CPU determines a predetermined interval by counting M clock pulses, and stores this M as an interval set value. That is, at the first time T ₁ ′ of a certain interval, the clock count value is counted from 0, and the clock count value is counted when M clock pulses are counted and time T ₂ ′ is reached and one interval is completed. Is reset to 0. If, when the clock count value immediately after receiving the certain interval signal is a m _1, the time at this time is _{T 1 '+ (m 1 /} M). If the clock count value immediately after receiving the next interval signal is m ₂ , the time at this time is T ₂ ′ + (m ₂ / M).

Interval calibration means that the receiving CPU counts the number of clock pulses per interval (for example, 1 ms) from the reception of a certain interval signal to the reception of the next interval signal, and the number of clock pulses Then, the value of the interval set value M is corrected. The number of clock pulses per interval is calculated from the difference between the time when the current and previous interval signals are received {T ₂ '+ (m ₂ / M)}-{T ₁ ' + (m ₁ / M)}. .

  Since the clock frequency mainly changes slowly with temperature change, interval calibration is performed using the average value of the number of clock pulses per interval in a predetermined number of intervals from the time when the interval signal was received a predetermined number of times before. . Specifically, when a predetermined number of intervals cannot be obtained, interval calibration is performed using the average value of the number of clock pulses per interval obtained so far, and when a predetermined number of intervals are obtained. The obtained average value of the number of clock pulses per interval is compared with the interval setting value M set so far, and the interval setting value M is increased or decreased by +1 or -1. Such interval calibration can prevent erroneous interval calibration.

  When the interval calibration is completed, the process returns to step S21. Thereafter, every time an interval signal is received, interval calibration of the receiving CPU is performed so that the intervals coincide between the two CPUs. When interval calibration has not been performed for a predetermined time or more, it is understood that interval calibration has not been performed as a status failure.

  Next, the time calibration program will be described. When the time calibration program is started, as shown in FIG. 3, the transmission side CPU proceeds to step S31, and detects whether or not it is the transmission timing of the notification signal for notifying the current time transmission. The transmission timing is initially set to be a short time interval and gradually longer, and after a predetermined time (after 5 seconds), becomes a constant time interval. For example, the transmission timing is gradually longer, such as 0 ms later, 256 ms later, 512 ms later, 1024 ms later, 2048 ms later, 4096 ms later, and twice the previous time interval, but after 4096 ms, 4096 ms later. At regular intervals. Note that the transmission timing does not necessarily follow an exact rule. If it is not the transmission timing, the process returns to step S31.

  At the transmission timing, the process proceeds to step S32, and a notification signal is transmitted from the transmission CPU to the reception CPU. Then, the process immediately proceeds to step S33, and as shown in FIG. 4, the notification signal transmission time is calculated as T + n / N of the current time from the clock count value n of the transmission side CPU. Next, proceeding to step S34, the notification signal transmission time T + n / N is transmitted from the transmission CPU to the reception CPU. Next, the process proceeds to step S35, the next transmission timing is determined, and the process returns to step S31. Thereafter, steps S31 to S35 are repeated, and the notification signal and the notification signal transmission time are transmitted from the transmission side CPU to the reception side CPU at a predetermined timing.

  By the way, when another receiving CPU is connected in series to the receiving CPU and an interval signal is transmitted from this receiving CPU to another receiving CPU, when the time of the receiving CPU is calibrated, the interval becomes Since it goes out of order, the interval signal is not transmitted to another receiving CPU twice. In such a case, the transmission timing of the transmitting CPU is returned to the initial state with the minimum time interval so that synchronization can be achieved in a short time.

On the other hand, when the time calibration program is started, the receiving CPU proceeds to step S41 and checks whether a notification signal has been received. If the notification signal has not been received, the process returns to step S41. If, if the received broadcast signal, the process proceeds to step S42, as shown in FIG. 4, it acquires the broadcast signal reception time T '+ m 1 _{/ M} clock count value m _1, immediately proceeds to step S43 Then, it waits so that the notification signal transmission time T + n / N transmitted from the transmission side CPU can be received. Upon receiving the report signal transmitting time T + n / N sent from the transmission side CPU, the process proceeds to step S44, acquires the current time _{T '+ p + m 2 /} M, i.e. the time calibration execution time from the clock count value _{m 2.}

Subsequently, the time calibration is performed after the notification signal is received from the difference p + m ₂ / M−m ₁ / M between the time T ′ + m ₁ / M acquired in step S 44 and the time T ′ + p + m ₂ / M acquired in step S 42. Calculate the elapsed time until execution. Next, the process proceeds to step S45, time calibration is performed to match the time of the receiving CPU with the time of the transmitting CPU, and the process returns to step S41. During this time calibration, the time required for the notification signal to be transmitted from the transmission CPU to the reception CPU at the notification signal transmission time T + n / N transmitted from the transmission CPU (serial calculated from the baud rate). (Communication transmission time) q and time T + n / N + p + m ₂ / M-m ₁ / M, which is the sum of elapsed time p + m ₂ / M−m ₁ / M from reception of the notification signal to time calibration The time of the receiving CPU is adjusted. Thereafter, the time of the receiving CPU is calibrated at a predetermined timing.

  In this time calibration, if the processing of the receiving CPU has not caught up and received a plurality of notification signals, or if the time for time calibration has passed a predetermined time or more after receiving the notification signal, an error will occur. Time calibration is not performed. When time calibration is not performed for a predetermined time or more, it is determined that the status is bad and it is understood that time calibration is not performed.

  Thus, the receiving CPU can synchronize time with the transmitting CPU by interval calibration and time calibration.

  According to the present embodiment, the time is calibrated so that the receiving CPU matches the time of the transmitting CPU at a predetermined timing, so that each CPU can always be kept in time synchronization. At this time, the time required for the notification signal to be transmitted from the transmission CPU to the reception CPU at the notification signal transmission time from the transmission CPU, and the time from the reception CPU receiving the notification signal to the time calibration. Since the time is calibrated at the time when the elapsed time is added, the time synchronization error can be minimized. In addition, since the timing for time calibration is initially set to be gradually longer at short time intervals, the receiving CPU can shift from a state where time synchronization is not achieved to a state where time synchronization can be achieved in a short time. Then, after a predetermined time, it is possible to prevent time synchronization from being lost because each CPU periodically synchronizes time at a fixed timing. Furthermore, when the receiving side CPU receives the notification signal a plurality of times, or when the time for performing the time calibration at the receiving side CPU has passed a predetermined time or more from the reception of the notification signal, the time calibration is not performed. Obviously wrong time synchronization and time synchronization with a large error can be avoided.

  Furthermore, in this embodiment, since interval calibration is performed at a predetermined interval, once the time is calibrated, the difference in the time advance between the two CPUs is reduced, and the time calibration interval can be extended. Become. In addition, a clock count value per interval is calculated from the time when the previous interval signal is received and the time when the current interval signal is received, and the clock count value is calculated with respect to the clock count value calculated from the clock frequency. Since the interval calibration is performed within ± 1%, it is possible to prevent interval calibration when a notification signal is not transmitted or when an apparently incorrect clock count value is obtained. The gap can be made even smaller. Further, the interval calibration is performed with the average value of the number of clock pulses per interval obtained until the predetermined number of intervals is reached, and after reaching the predetermined number of intervals, Compare the interval setting value with the average value of the number of clock pulses per interval in the predetermined number of intervals, and increase or decrease the interval setting value by +1 or −1. Highly accurate interval calibration can be maintained.

  By the way, the present invention is not limited to the above embodiment, and various modifications are possible. For example, in the above embodiment, only time synchronization between two CPUs has been described, but a plurality of receiving CPUs can be connected in series or in parallel to the transmitting CPU.

The flowchart of the interval calibration program of this invention. The figure explaining the method of interval calibration. The flowchart of the time calibration program of this invention. Diagram explaining time calibration method

Claims (7)

In the time synchronization system in which the time is synchronized between the sending CPU and the receiving CPU,
The transmission-side CPU includes notification signal transmission means for transmitting a notification signal for notification of current time transmission according to a predetermined transmission timing, notification signal transmission time acquisition means for acquiring the transmission time of the notification signal, and notification signal transmission time. A notification signal transmission time transmission means for transmitting,
The receiving CPU includes a notification signal receiving unit that receives a notification signal, a notification signal reception time acquisition unit that acquires a time when the notification signal is received, a notification signal transmission time reception unit that receives a notification signal transmission time, and a notification Time calibrating means for calibrating the time to a time obtained by adding the time required for the notification signal to be transmitted from the transmitting CPU to the receiving CPU at the signal transmission time and the elapsed time from the notification signal receiving time to the time calibration execution is provided. A time synchronization system characterized by that.   2. The time synchronization system according to claim 1, wherein the transmission timing is initially set to be a short time interval and gradually increases, and becomes a constant time interval after a predetermined time.   The time calibration is not performed when the notification signal is received a plurality of times, or when the time for performing the time calibration has passed a predetermined time or more from the notification signal reception time. 2. The time synchronization system according to 2. The transmitting CPU includes interval signal transmitting means for transmitting an interval signal at a predetermined interval,
The receiving CPU calculates the number of clock pulses per interval from interval signal reception time acquisition means for acquiring the time at which the interval signal is received, and the current interval signal reception time and the previous interval signal reception time. 2. A clock counting means, and interval calibration means for calibrating an interval set value set in a receiving CPU so that the intervals coincide between the transmitting CPU and the receiving CPU. The time synchronization system according to 2 or 3.   The number of clock pulses per interval is calculated from the time when the previous interval signal was received and the time when the current interval signal was received, and the number of clock pulses is calculated based on the clock frequency. 5. The time synchronization system according to claim 4, wherein the interval calibration is performed within ± 1%.   6. The time synchronization system according to claim 4, wherein the interval calibration is performed by using an average value of the number of clock pulses per interval in a predetermined number of intervals.   The interval calibration calibrates with the average value of the number of clock pulses per interval obtained until the predetermined number of intervals is reached, and after reaching the predetermined number of intervals, the receiving CPU The interval setting value is compared with an average value of the number of clock pulses per interval in the predetermined number of intervals, and the interval setting value is increased or decreased by +1 or -1. Time synchronization system.

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