DE102019206137A1 - Method for synchronizing a time base of a slave to a time base of a master and arrangement - Google Patents

Abstract

The invention relates to a method for synchronizing a time base (21) of a slave (4) to a time base (20) of a master (2), these communicating via a signal line (6), comprising the steps: a) impressing a request signal sequence (10 ) with a request synchronization event (11) on the signal line (6) by means of the slave (4), the slave (4) recording a request sending time stamp (TS1) at the time of sending the request synchronization event (11), b) receiving the request signal sequence (10) by means of the Masters (2) via the signal line (6), c) impressing a response signal sequence (12) with a response synchronization event (13) on the signal line (6) by means of the master (4), the master (2) sending a response time stamp (TM) to the The sending time of the response synchronization event (13) is recorded and transmitted to the slave (4), d) receiving the response signal sequence (12) by means of the slave (4), with a response reception time stamp (TS2) for receiving gszeitpunkt the response synchronization event (13) is detected, e) estimating the time base (20) of the master (2) on the basis of the time stamp (TS1, TS2, TM) by means of the slave (4), f) adapting the time base (21) of the slave (4) on the estimated time base (20) of the master (2). The invention also relates to an arrangement (1).

Description

The invention relates to a method for synchronizing a time base of a slave to a time base of a master and to an arrangement.

In arrangements of electronic control devices, for example in motor vehicles, it is essential for the acquisition of measured values and for the execution of commands that the individual control devices have a synchronized time base.

From the DE 10 2011 003 345 A1 it is known to transmit time and clock information from a control unit operating as a master to a control unit operating as a slave. Another method for synchronizing control devices in a master-slave arrangement is from the DE 10 2014 107 305 A1 known.

The invention is based on the object of creating a method for synchronizing a time base of a slave to a time base of a master and an arrangement in which the synchronization is improved.

According to the invention, the object is achieved by a method having the features of claim 1 and an arrangement having the features of claim 10. Advantageous embodiments of the invention emerge from the subclaims.

1. a) Aufprägen einer Anfragesignalsequenz auf die elektrische Signalleitung mittels des Slaves, wobei die Anfragesignalsequenz ein Anfragesynchronisationsereignis umfasst, und wobei der Slave lokal einen Anfragesendezeitstempel zum Sendezeitpunkt des Anfragesynchronisationsereignis erfasst,
2. b) Empfangen der Anfragesignalsequenz mittels des Masters über die elektrische Signalleitung,
3. c) Aufprägen einer Antwortsignalsequenz auf die elektrische Signalleitung mittels des Masters, wobei die Antwortsignalsequenz zumindest ein Antwortsynchronisationsereignis umfasst, wobei der Master lokal einen Antwortsendezeitstempel zum Sendezeitpunkt des Antwortsynchronisationsereignis erfasst und an den Slave übermittelt,
4. d) Empfangen der Antwortsignalsequenz mittels des Slaves, wobei ein Antwortempfangszeitstempel zum Empfangszeitpunkt des Antwortsynchronisationsereignis erfasst wird,
5. e) Schätzen der Zeitbasis des Masters auf Grundlage des erfassten Anfragesendezeitstempels, des erfassten Antwortempfangszeitstempels und des empfangenen Antwortsendezeitstempels mittels des Slaves,
6. f) Anpassen der Zeitbasis des Slaves auf Grundlage der geschätzten Zeitbasis des Masters.

In particular, a method is provided for synchronizing a time base of a slave to a time base of a master, the slave and the master communicating with one another via an electrical signal line reserved for this purpose, comprising the steps:

1. a) impressing a request signal sequence on the electrical signal line by means of the slave, wherein the request signal sequence comprises a request synchronization event, and wherein the slave locally detects a request sending time stamp at the time of sending the request synchronization event,
2. b) receiving the request signal sequence by means of the master via the electrical signal line,
3. c) impressing a response signal sequence on the electrical signal line by means of the master, the response signal sequence comprising at least one response synchronization event, the master locally acquiring a response transmission time stamp at the transmission time of the response synchronization event and transmitting it to the slave,
4. d) Receiving the response signal sequence by means of the slave, with a response reception time stamp being recorded at the time the response synchronization event is received,
5. e) Estimating the time base of the master on the basis of the recorded request transmission time stamp, the recorded response reception time stamp and the received response transmission time stamp by means of the slave,
6. f) Adjusting the time base of the slave based on the estimated time base of the master.

Furthermore, an arrangement is created comprising a master with a time base, at least one slave with a time base, and at least one reserved electrical signal line via which the at least one slave can communicate with the master, the at least one slave being designed in such a way as to provide a request signal sequence impressing on the electrical signal line, the request signal sequence including a request synchronization event, and locally detecting a request sending time stamp at the sending time of the request synchronization event; and wherein the master is designed to receive the request signal sequence via the electrical signal line and then impress a response signal sequence on the electrical signal line, the response signal sequence comprising at least one response synchronization event, and locally to detect a response transmission time stamp at the transmission time of the response synchronization event and to transmit it to the slave ; and wherein the at least one slave is further configured to receive the response signal sequence and thereby to acquire a response reception time stamp at the time of receipt of the response synchronization event, and to estimate the time base of the master on the basis of the acquired request transmission time stamp, the acquired response reception time stamp and the received response transmission time stamp, and the time base of the slave based on the estimated time base of the master.

The method and the arrangement make it possible to synchronize a time base of a slave to a time base of a master via an electrical signal line reserved for this purpose. Synchronizing the In this context, time bases should in particular mean that a time on a clock of the slave is aligned with a time on a clock of the master. The electrical signal line exists exclusively between the master and the slave. If further slaves are to be synchronized to the time base of the master, further electrical signal lines are provided accordingly. At the beginning of the process, the slave generates a request in the form of a request signal sequence, which is impressed on the electrical signal line by setting appropriate voltage values. The request signal sequence here includes signals, in particular electrical high and low voltage values. The request signal sequence includes a request synchronization event. A request sending time stamp, that is to say a point in time at which the request synchronization event is sent from the slave within the request signal sequence, is recorded by means of the slave and stored, for example, in a memory of the slave. The request sending time stamp shows the time base of the slave. The master receives the query signal sequence and then generates a response signal sequence. The response signal sequence includes at least one response synchronization event. The response signal sequence generated is impressed on the electrical signal line by means of the master by setting appropriate voltage values. The response signal sequence here includes signals, in particular electrical high and low voltage values. A response transmission time stamp, that is to say a point in time at which the response synchronization event is sent from the master within the response signal sequence, is recorded by the master and likewise transmitted to the slave. The response transmission time stamp has the time base of the master and can, for example, also be transmitted to the slave as part of the response signal sequence. The slave receives the response signal sequence via the electrical signal line and in doing so detects a response reception time stamp at the time of receipt of the response synchronization event, that is to say the time at which the response synchronization event is received by the slave. The slave then estimates the time base of the master on the basis of the acquired request transmission time stamp, the acquired response reception time stamp and the received response transmission time stamp and adjusts the time base of the slave based on the estimated time base.

In the simplest case, the time base of the slave can be adjusted by adopting the estimated time base of the master. However, it can also be provided that the time base of the slave is gradually adapted to the estimated time base of the master.

The advantage of the method and the arrangement is that it is possible to implement a time synchronization via a single electrical signal line, which enables a high degree of synchronization accuracy. In particular, the defined synchronization events make it possible to precisely define times within the communication between the master and the slave, on the basis of which a time base of the master can be estimated with high accuracy. This enables reliable time synchronization. Reliability of the time synchronization refers to the fact that the time synchronization can be implemented in terms of synchronization accuracy with regard to operational safety in a quality from Automotive Safety Integrity Level (ASIL) A to ASIL D according to ISO 26262.

The terms master and slave each refer to control devices that work together according to the master-slave principle. In connection with the invention, this means that the slave synchronizes a time base to a time base of the master, that is, the master specifies a common time base or a time for a clock of the slave. The control devices can be designed as a combination of hardware and software, for example as program code that is executed on a microcontroller or microprocessor.

• - die Zeitbasen bzw. die Uhren selbst sind ASIL-tauglich und manipulationssicher,
• - die Zeitbasen sind streng monoton steigend,
• - eine bestimmte Taktgenauigkeit liegt in einem vorgegebenen Bereich (z.B. +/- 100 ppm),
• - eine vorgegebene Auflösung (z.B. 1 ns) wird erreicht und
• - eine vorgegebene Ablesegenauigkeit (z.B. 1 ns) wird erreicht.

In connection with the method and the arrangement, it is assumed in particular that the time bases or clocks in the master and in the slave, which provide these time bases, meet certain properties:

• - the time bases or the clocks themselves are ASIL-compatible and tamper-proof,
• - the time bases are strictly increasing,
• - a certain clock accuracy is in a given range (e.g. +/- 100 ppm),
• - A specified resolution (eg 1 ns) is achieved and
• - A specified reading accuracy (eg 1 ns) is achieved.

The signal line is designed in particular as an electrical signal line. This means that signals in electrical form, for example as voltage pulses, can be impressed and received on the signal line at least at its ends or interfaces to the master and the slave. It is however, it is possible that the signal line between the ends is at least partially non-electrical, for example signals can also be transmitted in sections wirelessly or via optical waveguides. In this case, the signal line includes corresponding converters so that electrical signals can be used again at their ends.

The request synchronization event and the response synchronization event are arranged in particular at marked positions within the signal sequences, that is to say at positions which are known to the master and the slave. If the signal sequence is, for example, a coded bit sequence, the synchronization events are each arranged at a specific position within this bit sequence. Both the master and the slave know the position of the respective synchronization event and can therefore record a time stamp in their local time base or on their local clock when the respective synchronization event occurs or is observed.

In one embodiment it is provided that a round trip time is calculated and checked by means of the slave on the basis of the recorded request transmission time stamp and the recorded response reception time stamp. For this purpose, the slave forms, for example, the difference between the recorded response reception time stamp and the recorded request transmission time stamp. The difference then corresponds to the round trip time. As part of the review of the round trip time, the calculated round trip time can be compared with a threshold value, for example. If the calculated round trip time exceeds the threshold value or if this is equal to the threshold value, the result of the check is that the time synchronization is not integer. One reason for this can be a “man-in-the-middle” attack, in which an attacker has switched himself into the signal line and tries to disrupt or change a synchronization between the master and the slave. However, if the round trip time is below the threshold value, the result of the check is that the time synchronization is integer. The result is output as an analog or digital test signal, for example. Establishing the integrity of the time synchronization is one of the requirements for making the time synchronization secure against manipulation.

In one embodiment it is provided that the request signal sequence comprises an encoded challenge, the master generating and providing a response based on the challenge and the response signal sequence comprising the encoded response, and the received response being checked by the slave as a function of the challenge sent. This allows the master to be authenticated and / or authorized by the slave. Only if the master generates and transmits the correct response to the challenge is it assumed that the master is authentic or authorized. In order to protect the time synchronization against replay attacks, it is essential that the challenge follows an unpredictable pattern. A check result can be provided and / or output, for example, in the form of a corresponding check result signal. A response can be formed, for example, via an XOR operation from an identification code transmitted by the slave and information known only to the slave and the master. The authentication and / or authorization of the master can meet a further requirement in order to make the time synchronization secure against manipulation.

Fulfilling the aforementioned requirements is particularly advantageous if it is not ensured that all connections, that is to say all sections of the signal line, between the master and the slave can be classified as trustworthy.

In one embodiment it is provided that the estimation of the time base of the master takes place on the basis of a linear extrapolation function. In the simplest case, the linear extrapolation function is formed on the basis of the recorded request transmission time stamp, the recorded response reception time stamp and the received response transmission time stamp. An estimate of the time base of the master can then be carried out for any point in time.

wobei tm die geschätzte Zeitbasis des Masters ist, ts die Zeitbasis des Slaves, TS2 der Antwortempfangszeitstempel, TM der Antwortsendezeitstempel und RND eine unbekannte Antwortverzögerung, welche in einem Intervall von 0 und der Rundreisezeit (TS2 - TS1) liegt. Die unbekannte Antwortverzögerung führt zu einem Fehler beim Schätzen der Zeitbasis des Masters. Sind alle Werte erfasst bzw. empfangen, so kann über die oben angegebene Gleichung mittels des Slaves die Zeitbasis des Masters geschätzt werden.For example, the linear extrapolation function is as follows: $$\text{tm}\left(\text{ts}\right)=\left(\text{ts-TS2}\right)+\text{TM}+\text{RND}\text{,}$$

where tm is the estimated time base of the master, ts the time base of the slave, TS2 the response reception timestamp, TM the reply send timestamp and RND an unknown response delay, which occurs in an interval of 0 and the round trip time ( TS2 - TS1 ) lies. The unknown response delay results in a Error in estimating the time base of the master. Once all values have been recorded or received, the time base of the master can be estimated using the above equation using the slave.

In a further embodiment, it is provided that the master locally records a request input time stamp at the time of receipt of the request synchronization event, the response signal sequence additionally including the recorded request input time stamp, and the estimation of the time base of the master also taking place on the basis of the received request input time stamp. As a result, a period of time which the master needs after receiving the request signal sequence in order to provide the response signal sequence can be taken into account when estimating the time base of the master. This can reduce an error when estimating the time base of the master.

In one embodiment it is provided that the query synchronization event is arranged at a start of the query signal sequence and the response synchronization event is arranged at an end of the response signal sequence. At the beginning of this is intended to mean that the query synchronization event is temporally arranged at a position as far forward as possible in the query signal sequence. At one end is intended to mean that the response synchronization event is temporally arranged at a position as far back as possible in the response signal sequence. In simple terms, an attack on the time synchronization between master and slave can be detected in the period between the two synchronization events, but not outside of it, that is to say before the request synchronization event and after the response synchronization event. By arranging the synchronization events as far as possible at the beginning and at the end within the signal sequences, this period of time can be increased so that an attack can be detected over a longer period and time synchronization is more reliable.

In a further embodiment it is provided that a digital signature is generated by means of the master and is transmitted to the slave as part of the response signal sequence, the digital signature being checked by means of the slave. This allows the authenticity and / or authorization of the master to be checked. In particular, it is provided here that a response to a challenge of the slave transmitted to the master is inserted into the response signal sequence of the master and the digital signature is also calculated using this challenge. Since only the slave and the master know an underlying secret for deriving a response to the challenge, the slave can uniquely identify the master as the sender of the response signal sequence. This makes it possible to identify whether the response signal sequence was manipulated when it was transmitted via an untrustworthy signal line. In particular, this can protect the time synchronization from replay attacks. By authenticating and / or authorizing the master using the digital signature, time synchronization can be made even more secure against manipulation.

In a development it is provided that the digital signature and / or the request signal sequence and / or the response signal frequency are generated or encrypted by means of cryptographic methods. For example, the AES-256 method can be used.

In one embodiment it is provided that the query signal sequence and the response signal sequence are designed as binary codings.

In a further development, it is provided that the binary information of the bits in the binary coding is expressed in each case via a level change, the query synchronization event and the response synchronization event each corresponding to level changes, which are each arranged at marked positions in the sequences. This allows time stamps for the synchronization events to be recorded particularly well. It is also possible to provide the synchronization events with a higher temporal resolution if the edges are designed to be correspondingly steep during the level changes. In particular, it is possible to implement the signal sequences using inexpensive microcontrollers with digital inputs / outputs with an interrupt function. Furthermore, the electrical signal line can be formed between master and slave via a pair of input and output. The digital inputs are then operated in such a way that a corresponding interrupt is triggered each time the level changes. This enables cost-effective synchronization of master and slave to be implemented. The Manchester code, for example, can be used as coding.

In one embodiment it is provided that the request signal sequence and / or the response signal sequence include at least one additional item of information. This can, in particular, be a checksum (CRC) and / or a unique identification feature for the sequences and / or a unique one Be an identification feature for the master or the slave and / or a unique identification feature for the time base. This can further improve the synchronization between master and slave.

In one embodiment it is provided that the response transmission time stamp is transmitted separately to the slave following the response signal sequence. This can take place in particular in the form of a directly following signal sequence. As a result, synchronization accuracy can be further improved, since as a rule a recorded response transmission time stamp can only be provided after the response signal sequence has already been transmitted. The reply send time stamp can also be estimated, but it can deviate from a real reply send time, for example due to a delay in the processing of individual tasks in a microcontroller of the master.

wobei die bereits bekannten Bezeichnungen jeweils durch einen Index für die Synchronisationszyklen gekennzeichnet wurden. In der linearen Extrapolationsfunktion wird das Ratenverhältnis RR dann wie folgt berücksichtigt: $$\text{tm}\left(\text{ts}\right)=\left(\text{ts}-\text{TS2}\right)*\text{RR}+\text{TM}+\text{RND}$$

Um einen absoluten Fehler beim Erfassen der Zeitstempel TM_x und TSx zu minimieren, wird ein zeitlicher Abstand zwischen den Synchronisationszyklen möglichst groß gewählt.It can be provided that the time base of the master is estimated on the basis of at least two synchronization cycles. This can be done, for example, in the form of a rate adjustment. For this purpose, the time stamps of, for example, two synchronization cycles are set in relation to one another. The following then results for a rate ratio RR: $$\text{RR =}\left(\text{TM\_2-TM\_1}\text{,}\right)\text{/}\left(\text{TS}2\_2-\text{TS}2\_1\right)\text{,}$$

The names that are already known have been identified by an index for the synchronization cycles. In the linear extrapolation function, the rate ratio RR is then taken into account as follows: $$\text{tm}\left(\text{ts}\right)=\left(\text{ts}-\text{TS2}\right)*\text{RR}+\text{TM}+\text{RND}$$

In order to minimize an absolute error when capturing the time stamps TM_x and TSx, a time interval between the synchronization cycles is selected as large as possible.

Features for the configuration of the arrangement result from the description of configurations of the method. The advantages of the arrangement are in each case the same as in the embodiments of the method.

• 1 eine schematische Darstellung einer Ausführungsform der Anordnung;
• 2 eine schematische Darstellung eines zeitlichen Ablaufs des Verfahrens zur Verdeutlichung des Schätzens der Zeitbasis des Masters.

The invention is explained in more detail below on the basis of preferred exemplary embodiments with reference to the figures. Here show:

• 1 a schematic representation of an embodiment of the arrangement;
• 2 a schematic representation of a time sequence of the method to illustrate the estimation of the time base of the master.

In 1 Figure 3 is a schematic representation of one embodiment of the arrangement 1 shown. The order 1 includes a control unit that acts as a master 2 occurs. The master 2 shows a clock 3 with a time base 20th on. The arrangement also includes 1 a control unit that acts as a slave 4th occurs. The slave 4th shows a clock 5 with a time base 21st on. To synchronize the time base 21st the clock 5 of the slave 4th on the time base 20th the clock 4th of the master 2 communicate the master 2 and the slave 4th via a signal line 6 . This signal line 6 is in particular an electrical signal line.

It can be provided, for example, that the electrical signal line 6 between digital inputs and outputs of the master 2 and the slave 4th is trained. In particular, level changes on the electrical signal line can occur 6 trigger an interrupt at the digital inputs every time.

It can be provided that further control units act as further slaves 7th with the master 2 via further signal lines 8th connected and synchronized.

The slave 4th is designed in such a way, a request signal sequence 10 on the signal line 6 to impress, the request signal sequence 10 a request synchronization event 11 includes. The slave 4th When imprinted locally, records a request sending time stamp at the sending time of the request synchronization event 11 .

The master 2 is designed such that the request signal sequence 10 over the signal line 6 to receive and then a response signal sequence 12 on the signal line 6 to impress, with the Response signal sequence 12 at least one response synchronization event 13 includes. The master 2 records a response time stamp locally when stamped TM at the time the response synchronization event was sent 13 and transmits the captured response sending time stamp TM to the slave 4th .

The reply send timestamp TM can be used as part of the response signal sequence 12 be transmitted. Alternatively, it is also possible that the response time stamp TM in one of the response signal sequence 12 subsequent signal sequence is transmitted.

The slave 4th is also designed in such a way, the response signal sequence 12 over the signal line 6 and in this case a response reception time stamp at the time of receipt of the response synchronization event 13 capture.

The slave then estimates 4th the time base 20th of the master 2 based on the captured request sending time stamp, the captured response receiving time stamp, and the received response sending time stamp TM . The slave 4th fits the time base 21st the clock 5 then based on the estimated time base 20th of the master 2 on.

It can be provided that by means of the slave 4th a round trip time is calculated and checked based on the captured request sending time stamp and the captured response receiving time stamp.

It can also be provided that the request signal sequence 10 comprises an encoded challenge, the master 2 a response is generated and made available on the basis of the challenge and the response signal sequence 12 comprises the coded response, and wherein the received response by means of the slave 4th is checked depending on the challenge sent. The response can be, for example, as part of the query sequence 10 include transmitted identification code to which an XOR operation was applied with information known only to the slave and the master.

It can also be provided that the time base is estimated 20th of the master 2 is based on a linear extrapolation function.

It can be provided that the master 2 locally an incoming request timestamp at the time of receipt of the request synchronization event 11 detected, the response signal sequence 12 additionally comprises the captured inquiry receipt time stamp, and wherein estimating the time base 20th of the master 2 additionally takes place on the basis of the received request timestamp.

It can be provided that the query synchronization event 11 at a beginning of the query signal sequence 10 and the response synchronization event 13 at one end of the response signal sequence 12 are arranged.

It can further be provided that by means of the master 2 a digital signature is generated and as part of the response signal sequence 12 to the slave 4th is transmitted, the digital signature by means of the slave 4th is checked.

In a further development, it can be provided that the digital signature and / or the request signal sequence 10 and / or the response signal frequency 12 be generated or encrypted using cryptographic methods, for example using the AES-256 method.

It can be provided that the request signal sequence 10 and the response signal sequence 12 are designed as binary codes.

In a further development, provision can be made for the binary information of the bits in the binary coding to be expressed in each case via a level change, with the query synchronization event 11 and the response synchronization event 13 each correspond to level changes, each at marked positions within the sequences 10 , 12 are arranged.

In 2 is a schematic representation of a time sequence of the method to illustrate the estimation of the time base of the master 2 based on the recorded request send time stamp TS1 , of the response received timestamp captured TS2 and the received reply send time stamp TM shown.

The slave 4th sends a query signal sequence 10 via a signal line 6 to the master 2 , where a request send timestamp TS1 on a local clock of the slave 4th is detected at the point in time when a in the query signal sequence 10 included request synchronization event 11 is shipped.

The master 2 receives the query signal sequence 10 and creates a response signal sequence 12 which is then transmitted via the signal line 6 to the slave 4th is transmitted, with a response sending time stamp TM on a local clock of the master 2 is detected at the time a in the response signal sequence 12 contained response synchronization event 13 is shipped. The reply send timestamp TM is also sent to the slave 4th transmitted. This can be done as part of the response signal sequence 12 take place or in the context of a subsequently transmitted sequence.

The slave 4th receives the response signal sequence 12 and acquires a response reception time stamp TS2 on the local clock of the slave 4th at the time at which that in the response signal sequence 12 contained response synchronization event 13 Will be received.

The sequences shown 10 , 12 and the synchronization events shown 11 , 13 are chosen merely as examples and can also be designed differently or at other positions within the sequences 10 , 12 be arranged.

The slave then estimates 4th a time base of the master's clock 2 based on the recorded request send time stamp TS1 , of the response received timestamp captured TS2 and the received reply send time stamp TM .

wobei tm die geschätzte Zeitbasis des Masters 2 ist und ts die Zeitbasis des Slaves 4. RND ist eine unbekannte Antwortverzögerung, welche in einem Intervall zwischen 0 und der Rundreisezeit RTT (= TS2 - TS1) liegt und welche die unbekannte Zeit zwischen dem Absenden und dem Empfangen des Antwortsynchronisationsereignisses 13 beschreibt. Die unbekannte Antwortverzögerung RND führt zu einem Fehler beim Schätzen der Zeitbasis des Masters 2. Sind alle Werte erfasst bzw. empfangen, so kann über die oben angegebene Gleichung mittels des Slaves 4 die Zeitbasis des Masters 2 geschätzt werden.This is done using a linear extrapolation function, which looks, for example, as follows: $$\text{tm}\left(\text{ts}\right)=\left(\text{ts-TS2}\right)+\text{TM}+\text{RND}\text{,}$$

where tm is the estimated time base of the master 2 and ts is the time base of the slave 4th . RND is an unknown response delay, which occurs in an interval between 0 and the round trip time RTT (= TS2 - TS1) and which is the unknown time between sending and receiving the response synchronization event 13 describes. The unknown response delay RND leads to an error when estimating the time base of the master 2 . Once all values have been recorded or received, the above equation can be used using the slave 4th the time base of the master 2 to be appreciated.

Because the slave 4th cannot make any statement about where the response transmission timestamp TM within the interval TS1 : TS2 is, can delay the response RND two extreme cases occur which limit the range of possible values to an interval between 0 and the round trip time RTT establish. In the first extreme case is the response delay RND equal to the round trip time RTT , in the other extreme case is the response delay RND equals 0. The greatest possible error in estimating the time base of the master 2 is therefore determined by RTT .

The slave 4th when setting the linear extrapolation function for the response delay RND basically any value within the interval 0 : Select RTT and thereby determine the location of the error. The slave chooses 4th the value 0 So this causes its synchronized clock to go from 0 to a maximum RTT towards the master 2 pursues. Alternatively, the slave selects the value RTT for the response delay RND so this causes its clock to go from 0 to a maximum RTT towards the master 2 going on.

• TS1 = 10 ms,
• TS2 = 12 ms,
• TM = 16 ms, $$\text{RND=}\left[0:2\left(=\text{TS2}-\text{TS}1\right)\right]\text{ms}\text{,}$$
  

so ergibt sich die folgende lineare Extrapolationsfunktion: $$\text{tm}\left(13\right)=\left(\text{13 ms-12 ms}\right)+16\text{ ms}+\text{RND}$$

$$\text{Extremfall 1:tm }\left(13\text{ ms}\right)=\left(13\text{ ms-12 ms}\right)+16\text{ ms}+\text{2 ms}=\text{19 ms}$$

$$\text{Extremfall 2:tm }\left(13\text{ ms}\right)=\left(13\text{ ms-12 ms}\right)+16\text{ ms}+\text{0 ms}=\text{17 ms}$$

For example, if the values recorded or received are the following:

• TS1 = 10 ms,
• TS2 = 12 ms,
• TM = 16 ms, $$\text{RND =}\left[0:2\left(=\text{TS2}-\text{TS}1\right)\right]\text{ms}\text{,}$$
  

this results in the following linear extrapolation function: $$\text{tm}\left(13\right)=\left(\text{13 ms-12 ms}\right)+16\text{ms}+\text{RND}$$

$$\text{Extreme case 1: tm}\left(13\text{ms}\right)=\left(13\text{ms-12 ms}\right)+16\text{ms}+\text{2 ms}=\text{19 ms}$$

$$\text{Extreme case 2: tm}\left(13\text{ms}\right)=\left(13\text{ms-12 ms}\right)+16\text{ms}+\text{0 ms}=\text{17 ms}$$

The largest possible error is then 2 ms.

It can be provided that the master 4th In addition, an incoming request time stamp locally TM_IN at the time of receipt of the request synchronization event 11 detected, the response signal sequence 12 additionally the recorded request receipt time stamp TM_IN includes, and
where estimating the time base of the master 2 additionally based on the received request timestamp TM_IN he follows. This can reduce processing time MRI who the master 2 after receiving the query signal sequence 10 needed to get the response signal sequence 12 when estimating the time base of the master 2 be taken into account. This can lead to an error when estimating the time base of the master 2 be reduced.

It then results: $$\text{MRT = TM-TM\_IN}$$

$$\text{Extremfall 2:RND}=\text{0}$$

This leads to a reduction in the greatest possible error: $$\text{Extreme case 1: RND = RTT-MRT}$$

$$\text{Extreme case 2: RND}=\text{0}$$

The largest possible error is then RTT - MRT <RTT.

This can further reduce errors in synchronization.

The slave 4th can also include the round trip time RTT check against a threshold. Is the round trip time RTT greater than or equal to the threshold value, there is a probability that the signal line 6 has been manipulated. In this case, the synchronization accuracy is judged to no longer have integrity and a corresponding check result is output as a check signal.

List of reference symbols

1

arrangement

2

master

3

Clock

4th

Slave

5

Clock

6th

Signal line

7th

another slave

8th

further signal line

10

Query signal sequence

11

Request synchronization event

12

Response signal sequence

13th

Response synchronization event

20th

Time base (master)

21st

Time base (slave)

TM

Reply send timestamp

TM_IN

Incoming request timestamp

TS1

Request send timestamp

TS2

Response reception timestamp

RND

Response delay

RTT

Round trip time

MRI

Processing time

QUOTES INCLUDED IN THE DESCRIPTION

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Patent literature cited

• DE 102011003345 A1 [0003]
• DE 102014107305 A1 [0003]

Claims (10)

Method for synchronizing a time base (21) of a slave (4) to a time base (20) of a master (2), the slave (4) and the master (2) communicating with one another via an electrical signal line (6) reserved for this purpose, comprising the steps: a) impressing a request signal sequence (10) on the electrical signal line (6) by means of the slave (4), wherein the request signal sequence (10) comprises a request synchronization event (11), and the slave (4) locally a request sending time stamp (TS1) at the time of sending the request synchronization event (11) recorded, b) receiving the request signal sequence (10) by means of the master (2) via the electrical signal line (6), c) impressing a response signal sequence (12) on the electrical signal line (6) by means of the master (4), wherein the response signal sequence (12) comprises at least one response synchronization event (13), the master (2) locally a response time stamp (TM) at the time of transmission the response synchronization event (13) is recorded and transmitted to the slave (4), d) receiving the response signal sequence (12) by means of the slave (4), a response reception time stamp (TS2) being recorded at the time of receipt of the response synchronization event (13), e) estimating the time base (20) of the master (2) on the basis of the recorded request transmission time stamp (TS1), the recorded response reception time stamp (TS2) and the received response transmission time stamp (TM) by means of the slave (4), f) Adaptation of the time base (21) of the slave (4) on the basis of the estimated time base (20) of the master (2). Procedure according to Claim 1 , characterized in that a round trip time (RTT) is calculated and checked by means of the slave (4) on the basis of the recorded request transmission time stamp (TS1) and the recorded response reception time stamp (TS2). Procedure according to Claim 1 or 2 , characterized in that the request signal sequence (10) comprises a coded challenge, wherein the master (2) generates and provides a response based on the challenge and the response signal sequence (12) comprises the coded response, and wherein the received response by means of the slave ( 4) is checked depending on the challenge sent. Method according to one of the preceding claims, characterized in that the time base (20) of the master (2) is estimated on the basis of a linear extrapolation function. Method according to one of the preceding claims, characterized in that the master (2) locally detects a request input time stamp (TM_IN) at the time of receipt of the request synchronization event (11), the response signal sequence (12) additionally including the recorded request input time stamp (TM_IN), and where the estimation the time base (20) of the master (2) is also based on the received request input time stamp (TM_IN). Method according to one of the preceding claims, characterized in that the query synchronization event (11) is arranged at a start of the query signal sequence (10) and the response synchronization event (13) is arranged at an end of the response signal sequence (12). Method according to one of the preceding claims, characterized in that the request signal sequence (10) and the response signal sequence (12) are designed as binary codings. Procedure according to Claim 7 , characterized in that the binary information of the bits are expressed in the binary coding in each case via a level change, the request synchronization event (11) and the response synchronization event (13) each corresponding to level changes which are each at marked positions in the sequences (10, 12 ) are arranged. Method according to one of the preceding claims, characterized in that the response transmission time stamp (TM) is transmitted separately to the slave (4) following the response signal sequence (12). Arrangement (1), comprising: a master (2) with a time base (20), at least one slave (4) with a time base (21), and at least one reserved electrical signal line (6) via which the at least one slave (4) can communicate with the master (2), the at least one slave (4) being designed to transmit a request signal sequence (10) to the electrical signal line (6) ) to impress, wherein the request signal sequence (10) comprises a request synchronization event (11), and locally to detect a request transmission time stamp (TS1) at the time of transmission of the request synchronization event (11); and wherein the master (2) is designed to receive the request signal sequence (10) via the electrical signal line (6) and then to impress a response signal sequence (12) on the electrical signal line (6), the response signal sequence (12) at least one response synchronization event (13) comprises, and locally detecting a response transmission time stamp (TM) at the transmission time of the response synchronization event (13) and transmitting it to the slave (4); and wherein the at least one slave (4) is further designed to receive the response signal sequence (12) and thereby record a response reception time stamp (TS2) at the time of receipt of the response synchronization event (13) and the time base (20) of the master (2) To estimate the basis of the recorded request transmission time stamp (TS1), the recorded response reception time stamp (TS2) and the received response transmission time stamp (TM), and to adapt the time base (21) of the slave (4) on the basis of the estimated time base (20) of the master (2).

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