A low-overhead time synchronization method based on wired connection

Abstract

A low-overhead time synchronization method based on wired connection includes a time synchronization method for each subordinate device and a main device, wherein the subordinate device and the main device are connected via a transmission channel, and the time synchronization method for the subordinate device and the main device includes the following steps: determining whether the subordinate device is performing time synchronization for the first time, if yes, performing two-way time synchronization, otherwise performing one-way time synchronization; the one-way time synchronization is to repeat multiple one-way data transmissions, record time data pairs, and use regression calculation to achieve one-way time synchronization. The time synchronization of the present invention adds a method for detecting channels, effectively reducing the single clock synchronization error, reducing the number of time synchronizations, reducing the occupancy of the transmission channel by time synchronization, and improving the utilization rate of the transmission channel.

Description

Technical Field

[0001] The invention belongs to the field of network communication, and in particular relates to a low-overhead time synchronization method based on wired connection. Background Art

[0002] Since the frequency of the local clock of each device has a certain error, the error will continue to accumulate over time, and the difference in time between devices will continue to expand. In the fields of communication, power, positioning, control, etc., devices need to complete specified actions at specified times, so the local time of each device needs to be highly consistent. Devices must be synchronized through continuous communication to ensure that the local clock of each device is maintained within a tolerable error range.

[0003] There are two types of time synchronization methods, one-way time synchronization and two-way time synchronization. Two-way time synchronization is a point-to-point method that sends data in both directions to offset the delay caused by propagation. The more nodes that need to be synchronized, the greater the overhead on time synchronization will be, which is not suitable for low-speed and large-scale networks. The one-way time synchronization method is a broadcast method, and its synchronization overhead is independent of the number of nodes. However, since the time from the sender to the receiver to obtain the timestamp is unknown, it will be affected by factors such as the interruption speed of the sender and the receiver, the transmission channel access delay, and the transmission delay, resulting in errors of several milliseconds to hundreds of milliseconds. Therefore, the estimation of these times will have a great impact on the accuracy of one-way time synchronization. Summary of the invention

[0004] In order to overcome the defects of the prior art, the present invention discloses a low-overhead time synchronization method based on wired connection.

[0005] The low-overhead time synchronization method based on wired connection of the present invention includes a time synchronization method of each subordinate device and a master device, wherein the subordinate device and the master device are connected via a transmission channel, and is characterized in that the time synchronization method of the subordinate device and the master device includes the following steps:

[0006] S0 determines whether the lower-level device is performing time synchronization for the first time, if so, two-way time synchronization is performed, otherwise one-way time synchronization is performed;

[0007] The specific method of the two-way time synchronization is:

[0008] S1. The sending device of the lower-level device submits the leading data;

[0009] S2. Record the time when the lower-level device detects the start of sending the leading data on the transmission channel and define it as T2.

[0010] S3. The lower-level device adds T2 to the data to be sent together;

[0011] S4. The master device detects whether there is a leading data sent by a lower device on the transmission channel, and the detected time is recorded as t1;

[0012] S5. The master device submits the leading data to its own sending device; the submission time is defined as t2

[0013] S6. The master device detects whether there is a leading data sent by the master device itself on the transmission channel, which indicates that the leading data starts to be sent, and the time when the sending starts is defined as t3;

[0014] S7. The master device adds t3 and t1 times to the data to be sent together;

[0015] S8. The lower device B detects whether there is a leading data sent by the master device in the transmission channel, and the detected time is recorded as T3;

[0016] S9. The subordinate device starts to process time synchronization and records the current time as T4, defines the third error Time3=T4-T3, and calculates the second error Time2=(T3-T2-(t3-t1)) / 2, and calculates the current time of the master device A as t4=t3+Time2+Time3. The subordinate device modifies its current time to t4, completing the two-way time synchronization between the subordinate device and the master device.

[0017] Preferably, the specific steps of the one-way time synchronization are:

[0018] S10. Record the sequence number as n, set the initial value of n to 0, and set the number of cycles N;

[0019] S11. The master device submits the leading data to its transmitting device, and the master device detects whether there is the leading data sent by itself on the transmission channel, and the detection time is t (n);

[0020] S12. The master device adds t(n) to the data to be sent;

[0021] S13. The lower-level device detects whether there is data on the transmission channel, and the detection time is recorded as T(n), forming a [t(n), T(n)] data pair;

[0022] S14. n plus 1, repeat steps S11 to S13 until n = N, then proceed to step S15;

[0023] S15. Perform regression calculation on all [(t(n),T(n)] data pairs, n∈[0,N-1];

[0024] The regression calculation formula is as follows:

[0025]

[0026] The subordinate device starts to process time synchronization, and defines the time of the subordinate device at this time as T5. According to the regression equation t=aT+b+Time2 in the first line of the regression calculation formula, let T=T5 and calculate the time corresponding to the master device.

[0027] t5 = a*T5+b+Time2;

[0028] The lower-level device changes the current time to t5, completing the one-way time synchronization of the lower-level device.

[0029] Preferably, the detection of whether there is data on the transmission channel is performed by an external interrupt controller in a device connected to the transmission channel. The detection method is to detect whether a rising edge or a falling edge appears on the transmission channel. If it does, an interrupt is triggered and it is determined that there is data on the transmission channel.

[0030] Preferably, the second error Time2 is approximately zero.

[0031] Preferably, the method further includes step S16, setting a repetition time interval according to the clock accuracy requirement of the lower-level device, and repeating steps S10 to S15.

[0032] Preferably, data transmission and reception between the device and the transmission channel is performed through a UART controller in the device connected to the transmission channel.

[0033] Preferably, the subordinate device communicates with the master device via the ModBus protocol, and the leading data is the address field and function code of the data in the ModBus protocol.

[0034] The present invention has the following technical advantages:

[0035] 1. The present invention effectively reduces the single clock synchronization error, can reduce the number of time synchronizations, reduce the occupancy of the transmission channel by time synchronization, and improve the utilization rate of the transmission channel.

[0036] 2. The present invention utilizes the stable topology of the wired network, and uses bidirectional time synchronization to point-to-point measure the signal propagation time when the device is connected, and is used for subsequent unidirectional time synchronization for a long time;

[0037] 3. The present invention uses a one-way time synchronization method based on broadcasting to maintain time synchronization, which occupies a small bandwidth and is suitable for low-speed but time-sensitive occasions;

[0038] 4. The present invention directly monitors the transmission channel, eliminating the time synchronization error caused by delays such as data encoding and decoding, waiting for clock signals, and system interruptions. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1A system block diagram in an embodiment of the present invention; wherein device A is a master device, and devices B and C are different subordinate devices that need to be synchronized with the clock of device A;

[0040] Figure 2 A schematic diagram of a specific flow chart of the time synchronization method of the present invention;

[0041] Figure 3 Schematic diagram of the time axis and data transmission timing of the master device A and the subordinate device B when performing time synchronization in an embodiment of the present invention,

[0042] In the figure, t represents the different time of device A, and T represents the different time of device B. DETAILED DESCRIPTION

[0043] The specific embodiments of the present invention are described in further detail below.

[0044] The technical solution adopted by the present invention is as follows: device A is defined as a master device, device B is defined as a synchronized subordinate device, and both device A and device B include their own sending device and receiving device for sending and receiving data, and detect whether there is data being sent or received on the transmission channel through a detection module connected to the transmission channel.

[0045] Device A and device B are connected through a transmission channel. The two usually need to be time-consistent as a complete system. The time of device B needs to be synchronized with that of device A. The time of device A is represented by t, and the time of device B is represented by T. In the present invention, time synchronization is performed by combining one-way time synchronization and two-way time synchronization.

[0046] The time error between the devices connected on the data transmission bus can generally be divided into four parts.

[0047] 1. The first error Time1 is caused by the time interval from when the sender prepares the time data to when the data is sent out;

[0048] 2. The second error Time2 caused by the time interval for data to be transmitted from the transmitting end of one device to the receiving end of another device through the transmission channel;

[0049] 3. The third error Time3 caused by the time interval from when the data is received by the receiving end to when it is processed by the receiving end;

[0050] 4. The fourth error Time4 is caused by the accuracy and stability of the clocks on both the sending and receiving ends.

[0051] By estimating the errors of these four parts and taking measures to eliminate them, the accuracy of one-way time synchronization can be improved. By directly detecting the channel data transmission time, the first error can be eliminated.

[0052] In bidirectional time synchronization, due to the principle of bidirectional time synchronization, the fourth error can be offset, and time synchronization can be performed by only calculating the second and third errors.

[0053] The low-overhead time synchronization method based on wired connection of the present invention comprises the following steps:

[0054] S0. Determine if device B is not performing time synchronization for the first time, jump to step S10,

[0055] If it is the first time to synchronize time, two-way time synchronization is performed, including:

[0056] S1. The sending device of device B submits the leading data at time T1;

[0057] S2. Device B detects the time when the leading data starts to be sent on the transmission channel and is defined as T2, then the first error Time1 = T2-T1;

[0058] However, the first error actually no longer exists because the time when the channel transmits data is directly detected in the subsequent steps S4, S6, and S11.

[0059] S3. Device B adds T2 to the data to be sent;

[0060] S4. Device A detects data on the transmission channel, and the time is recorded as t1;

[0061] S5. Device A submits the leading data to the sending device of device A; the submission time is defined as t2

[0062] S6. The time when device A detects the start of transmission of leading data on the transmission channel is defined as t3;

[0063] S7. Device A adds t3 and t1 to the data to be sent;

[0064] S8. Device B detects data on the transmission channel, and the time is recorded as T3;

[0065] S9. Device B starts processing time synchronization and records the current time as T4, then the third error Time3 = T4-T3;

[0066] Since the time required for device A to send data to device B is approximately equal to the time required for device B to send data to device A, the second error Time2=(T3-T2-(t3-t1)) / 2 can be calculated. Therefore, the current time of device A can be estimated to be t4=t3+Time2+Time3. Device B changes the current time to t4, completing two-way time synchronization.

[0067] S10. When performing one-way time synchronization, the sequence number is n, and the initial setting n = 0;

[0068] S11 device A submits the leading data to its own transmitting device, and device A detects the time t (n) when the leading data starts to be sent on the transmission channel;

[0069] S12. Device A adds t(n) to the data to be sent;

[0070] S13. Device B detects whether there is data on the transmission channel, and the detected time is recorded as T (n), forming a [t (n), T (n)] data pair;

[0071] S14. n=n+1, when n=N, jump to S15, otherwise jump to S11; N is the set number of loops;

[0072] S15. Device B starts processing time synchronization at T5, and performs regression calculation on all [(t(n), T(n)] data pairs, n∈[0, N-1], to reduce the impact of the fourth error Time4.

[0073] The regression calculation formula is as follows:

[0074]

[0075] According to the regression equation of t=aT+b+Time2 in the first line of the above formula, substitute the T5 time of device B and set T=T5 to estimate the time corresponding to device A when the time of device B is T5.

[0076] t5 = a*T5+b+Time2

[0077] Device B changes the current time to t5, completing one-way time synchronization;

[0078] The specific process and timing are as follows Figure 2 and Figure 3 shown.

[0079] S16. Set the repetition time interval according to the clock accuracy, stability and clock synchronization accuracy requirements of device B, and repeat steps S10 to S15.

[0080] Among them, the second error Time2 is usually smaller than the other errors. If the wire length is short, or the synchronization accuracy requirement is not extremely high, Time2 is very small and can be ignored. Then some steps can be omitted and the second error Time2 can be directly regarded as 0.

[0081] The leading data may be replaced by other data before the data field. For example, the address field and function code of the ModBus protocol may be used as the leading data.

[0082] Figure 1 In the specific implementation shown, the transmission channel can be detected using an external interrupt controller of a single-chip microcomputer. Whether there is data on the transmission channel is detected by an external interrupt controller connected between the transmission channel and the device. The detection method is to detect whether a rising edge or a falling edge appears on the transmission channel. If it appears, an interrupt is triggered and it is determined that there is data on the transmission channel. Data transmission and reception between the device and the transmission channel is performed by a UART controller connected to the transmission channel and the device.

[0083] When using an external interrupt controller for detection, in order to reduce unnecessary overhead of external interrupts on the device, in steps S2 and S11, the detection of the transmission channel can be enabled after the leading data is submitted. In steps S4 and S13, the detection of the transmission channel can be enabled after device B receives the leading data of the first byte. At this time, the second error Time2 needs to be increased by the time of transmitting the corresponding leading data. Specific embodiments

[0085] The system block diagram used in this embodiment is as follows Figure 1 As shown, the data transmission protocol takes the ModBus protocol based on the RS485 data bus as an example; the RS485 data bus includes a pair of data lines A+ and B-, which are respectively connected to the A port and the B port of all interfaces; the device time axis diagram of the time synchronization method is shown in Figure 2 As shown; the flowchart of the time synchronization method described is as shown Figure 3 As shown, the embodiment only demonstrates the method for time synchronization between device A and device B, and the rest is similar, specifically including the following steps:

[0086] S0. After device B accesses the network, time synchronization is initiated by device A or device B;

[0087] Specifically, if time synchronization is initiated by device A, device A needs to send a synchronization request to device B for a period of time before jumping to S1;

[0088] If it is determined that device B is not performing time synchronization for the first time, the process jumps to step S10; if it is the first time to perform time synchronization, bidirectional time synchronization is performed.

[0089] In this embodiment, Figure 1 As shown, both the sending device and the receiving device are Figure 1 The UART controller in the device and the external interrupt controller serve as a detection module to detect whether there is data being sent and received on the transmission channel, and the transmission channel is the RS485 bus.

[0090] S1 records the submission time T1 of the leading data submitted by the sending device of device B;

[0091] Specifically, S1 includes the following steps:

[0092] S101. If device B is not performing time synchronization for the first time, jump to step S10, otherwise B transmits the ModBus broadcast address and function code as leading data to the buffer of the UART controller;

[0093] S102. Device B turns on external interrupts, and the control port of the external interrupt controller is connected to the A+ line of the RS485 bus and is set to a falling edge trigger; at this time, the external interrupt controller acts as a detection module to detect whether there is data transmission on the transmission channel, and the RS485 bus is the transmission channel.

[0094] The trigger mechanism of the external interrupt controller is set to rising edge or falling edge trigger according to the characteristics of data transmission. When a rising edge is generated at the beginning of data transmission, a rising edge trigger can be used. When a falling edge is generated at the beginning of data transmission, a falling edge trigger can be used.

[0095] S2. Device B detects the moment T2 when the leading data on the channel starts to be sent. After the RS485 bus starts to send, the level on the A+ line changes from high to low, generating a falling edge, triggering the external interrupt of device B. B records the time T2 at this time. The first error Time1=T2-T1. Recording the time T2 can eliminate the error caused by Time1.

[0096] S3. Device B adds T2 to the buffer of the UART controller;

[0097] S4. The external interrupt controller of device A is connected to the A+ data line of the RS485 bus, and continuously detects the data on the A+ data line as the transmission channel. When data is transmitted, the falling edge is triggered, and the time is recorded as t1;

[0098] S5. Device A submits leading data to its own transmitting device, the UART controller, at time t2, and the leading data is sent through the storage buffer of the UART controller;

[0099] S6. Device A detects the transmission channel. After RS485 starts sending, a falling edge appears on A+. The time t3 is recorded.

[0100] S7. Device A adds t3-t1 to the storage buffer in the UART controller and sends it together;

[0101] S8. Device B detects data on the transmission channel, and the time is recorded as T3;

[0102] S9. Device B starts processing time synchronization and records the current time as T4. Then the third error Time3 = T4 - T3. And the second error Time2 = (T3 - T2 - (t3 - t1)) / 2 can be calculated. Therefore, the current time of Device A can be estimated as t4 = t3 + Time2 + Time3. Device B modifies the current time to t4 to complete two-way time synchronization.

[0103] S10. When one-way time synchronization is required, n = 0.

[0104] S11. Device A submits preamble data to its sending device. Device A detects the moment when the preamble data starts to be sent on the channel through an external interrupt, that is, the moment t(n) when the first falling edge appears on A+ of RS485 after Device A submits the preamble data.

[0105] S12. Device A adds t(n) to the data to be sent.

[0106] S13. Device B detects the data on the channel, and the detected moment is recorded as T(n), forming a data pair [t(n), T(n)].

[0107] S14. n = n + 1. When n < N, jump to S11; otherwise, jump to S15.

[0108] S15. Device B starts processing time synchronization at T5. Perform regression calculation on [(t(n), T(n)], n ∈ [0, N - 1] to reduce the influence of the fourth error Time4, obtain the regression equation, and substitute T5 to estimate the time of Device A corresponding to T5 as t5. Device B modifies the current time T5 to t5 to complete one-way time synchronization.

[0109] The fourth error is a variable error caused by different clock precisions and stabilities. However, within a short period, the clock errors of the master and slave devices can both be regarded as increasing linearly. The times of both and the absolute time will respectively form two linear functions with different slopes and intercepts. Therefore, through a linear function, the time function of the slave device can be mapped to the time function of the master device, and the function used for this mapping can be obtained through linear regression, and the jitter caused by the fourth error can be removed to reduce the influence of the fourth error on time synchronization.

[0110] Specifically, the steps of S15 include the following steps:

[0111] S1501. Use the least squares method to obtain the regression equation of t(n) and T(n).

[0112]

[0113] S1502. Device B obtains the current time T5;

[0114] S1503. Device B substitutes T5 into the regression equation to estimate the time t5 of device A at time T5;

[0115] S1504. Device B sets the local clock to t5;

[0116] S16. Repeat S11 to S15 after a certain interval according to the clock accuracy, stability and clock synchronization accuracy requirements of device B;

[0117] Specifically, according to the accuracy requirement of maintaining the clock error at 10ms and the clock stability at 20ppm, S11 to S15 need to be repeated every 500s to maintain clock synchronization.

[0118] Based on the low-overhead time synchronization method based on wired connection, the channel data transmission time detection is used to eliminate the first error Time1 from the time when the sender prepares the time data to the time when the data is sent out;

[0119] In one-way time synchronization, since the slave device B detects and records the time T(n) when a signal appears on the channel, and obtains the current time T5 of the slave device B during time synchronization, the third error Time3 from the data received by the receiving end to the data processed by the receiving end is eliminated; the second error Time2 from the data transmitted from the sending end of one device to the receiving end of another device is basically eliminated through two-way time synchronization; the fourth error Time4 caused by the accuracy and stability of the clocks of both the sending and receiving ends is reduced through regression estimation. The accuracy of single time synchronization is improved with lower channel occupancy, and the frequency of time synchronization is reduced, thereby reducing the channel occupancy time for maintaining time synchronization.

[0120] If the functions described in the present invention are implemented in the form of software functional units and sold or used as independent products, they can be stored in a non-volatile computer-readable storage medium that can be executed by a processor. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for enabling a computer device (which can be a personal computer, a server or a network device) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk and other media that can store program codes.

[0121] The foregoing describes various preferred embodiments of the present invention. Unless the preferred implementation modes in various preferred embodiments are obviously self-contradictory or based on a certain preferred implementation mode, various preferred implementation modes can be arbitrarily superimposed and used in combination. The embodiments and specific parameters in the embodiments are only for clearly describing the invention verification process of the inventor, and are not used to limit the patent protection scope of the present invention. The patent protection scope of the present invention shall still be based on its claims. All equivalent structural changes made using the contents of the description and drawings of the present invention should be included in the protection scope of the present invention.

Claims

1. A low-overhead time synchronization method based on wired connection, comprising a time synchronization method for each subordinate device and a master device, wherein the subordinate device and the master device are connected via a transmission channel, It is characterized in that The time synchronization method between the subordinate device and the master device comprises the following steps: S0 determines whether the lower-level device is performing time synchronization for the first time, if so, two-way time synchronization is performed, otherwise one-way time synchronization is performed; The specific method of the two-way time synchronization is: S1. The sending device of the lower-level device submits the leading data; S2. Record the time when the lower-level device detects the start of sending the leading data on the transmission channel and define it as T2. S3. The lower-level device adds T2 to the data to be sent and sends it together; S4. The master device detects whether there is a leading data sent by the subordinate device on the transmission channel, and the detection time is recorded as t1; S5. The master device submits the leading data to its own sending device; the submission time is defined as t2 S6. The master device detects whether there is a leading data sent by the master device itself on the transmission channel. If yes, it indicates that the leading data starts to be sent, and the time when the sending starts is defined as t3; S7. The master device adds t3 and t1 times to the data to be sent and sends them together; S8. The lower-level device B detects whether there is a leading data sent by the master device on the transmission channel, and the time of detection is recorded as T3; S9. The subordinate device starts to process time synchronization and records the current time as T4, defines the third error Time3=T4-T3; and calculates the second error Time2=(T3-T2-(t3-t1)) / 2, and calculates the current time of the main device A as t4=t3+Time2+Time3. The subordinate device modifies its current time to t4, completing the two-way time synchronization between the subordinate device and the main device.

2. The low-overhead time synchronization method based on wired connection as claimed in claim 1, It is characterized in that The specific steps of the one-way time synchronization are: S10. Record the sequence number as n, set the initial value of n to 0, and set the number of cycles N; S11. The master device submits the leading data to its own sending device, and the master device detects whether there is the leading data sent by itself on the transmission channel, and the detection time is t(n); S12. The master device adds t(n) to the data to be sent; S13. The lower-level device detects whether there is data on the transmission channel, and the detection time is recorded as T(n), forming a [t(n), T(n)] data pair; S14. n is increased by 1, and steps S11 to S13 are repeated until n=N, and then step S15 is entered; S15. Perform regression calculation on all [(t(n), T(n)] data pairs, n∈[0, N-1]; The regression calculation formula is as follows: a is the first regression parameter, b is the second regression parameter, is the time mean of t, is the time mean of T, where T is the time of the subordinate device; t is the time corresponding to the master device when the time of the subordinate device is T; The subordinate device starts to process time synchronization, and defines the time of the subordinate device at this time as T5. According to the regression equation of t=aT+b+Time2 in the first line of the regression calculation formula, let T=T5 and calculate the time corresponding to the master device. t5=a*T5+b+Time2; The lower-level device changes the current time to t5, completing the one-way time synchronization of the lower-level device.

3. The low-overhead time synchronization method based on wired connection as claimed in claim 1, It is characterized in that The detection of whether there is data on the transmission channel is performed by an external interrupt controller in the device connected to the transmission channel. The detection method is to detect whether a rising edge or a falling edge appears on the transmission channel. If it does, an interrupt is triggered and it is determined that there is data on the transmission channel.

4. The low-overhead time synchronization method based on wired connection as claimed in claim 1, It is characterized in that The second error Time2 is approximately zero.

5. The low-overhead time synchronization method based on wired connection as claimed in claim 1, It is characterized in that The method further includes step S16, setting a repetition time interval according to the clock accuracy requirement of the lower-level device, and repeating steps S10 to S15.

6. The low-overhead time synchronization method based on wired connection as claimed in claim 1, It is characterized in that Data transmission and reception between the device and the transmission channel is performed through the UART controller in the device connected to the transmission channel.

7. The low-overhead time synchronization method based on wired connection as claimed in claim 1, It is characterized in that The subordinate device communicates with the master device via the ModBus protocol, and the leading data is the address field and function code of the data in the ModBus protocol.

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