GB2405063A

GB2405063A - Method and apparatus for transferring time-base information for synchronisation between clocked domains

Info

Publication number: GB2405063A
Application number: GB0318903A
Authority: GB
Inventors: Darioush Downer
Original assignee: NEC Technologies UK Ltd
Current assignee: NEC Technologies UK Ltd
Priority date: 2003-08-12
Filing date: 2003-08-12
Publication date: 2005-02-16
Also published as: GB0318903D0

Description

METHOD OF TRANFERRING TIME-BASE INFORMATION

BETWEEN CLOCKED DOMAINS AND RELATED APPARATUS

EMPLOYING THE SAME

The present invention relates to a method of transferring time-base information between clocked domains and to related apparatus arranged to employ such a method.

In systems employing a plurality of clocked domains, which typically operate asynchronously with respect to each other, it can prove desirable to transfer time base information therebetween in an attempt to enable synchronization between the two domains, wheresoever this is required for the whole system to operate.

It can be particularly desirable to achieve such synchronization between two clocked domains in situations in which each domain does not have any prior knowledge of the clock and time reference signals of the other domain.

Such clocked domains are commonly found in mobile radio communication devices such as cellular phone handsets in which it is desirable to provide for connectivity between different radio access technologies.

The different radio technologies would generally interfere with each other if used simultaneously and this makes mutually exclusive operation of the technologies desirable. Such mutual exclusivity of operation is commonly achieved synchronously by the control and allocation of scheduled operation of one radio access technology so as to allow access to the other technology.

The problem of establishing timing references between the different technologies often requires either central management for control of the exchange and conversion of information, or can require functionality changes within each domain with regard to the requirements for establishing the timebase of the other domain. However, given factors of legacy and novel the combination of radio technologies, the requirement for such changes can disadvantageously represent a burden. Further, within multi-mode handsets offering use with different radio access technologies, in order to combine different, or indeed add new, radio access technologies, which are capable of interoperating, changes to the synchronization mechanisms implemented for each of the radio access technologies become required.

However, due to the nature of the timing accuracy required for efficient interoperability between the different radio access technologies, the elements of each technology affected by the required changes tend to comprise the highest speed clocking domains. These usually prove to be the least easily changed elements in view of their requirement for dedicated hardware or committed firmware. The cost in achieving such changes can therefore prove disadvantageously, and potentially prohibitively, high.

The invention seeks to provide for a method of transferring timebase information between clocked domains, and to related apparatus having advantages over known such methods and apparatus.

According to a first aspect of the present invention, there is provided a method of transferring timing information from a first sub-system to a second sub-system of a system, the first and second sub-systems having different clocking domains and the method comprising the steps of, in the first sub- system generating a reference output signal indicating arbitrary events, and in the said second sub-system tracking its own reference timebase, storing its own reference time-base at least once and as triggered by the said arbitrary events within the signals from the said first subsystem, calculating time differences between stored values of its own timebase, and calculating a scaling factor of the time difference of its own timebase relative to that reported from the first said sub-system so as to employ said scaling factor for converting time values to achieve synchronization between the said sub- systems.

The present invention advantageously provides for a method for achieving a general-purpose, technology-neutral exchange of sufficient information after which it is possible to establish absolute and relative time measurements to coordinate each of the said first and second subsystems and without requiring any specific changes to be made to each of the subsystem.

Advantageously, synchronization between the two subsystems can be achieved without requiring prior information about the clocking information of each other subsystem.

Also, the said arbitrary events are generated at a frequency which is at most equivalent to the shortest minor time unit period that can be usefully measured by a clock of the other subsystem.

The arbitrary events may also be generated with a frequency at least equivalent to the longest major time unit period that can be usefully measured by the clock of the other subsystem.

Further, each subsystem is arranged to provide a list of at least values corresponding to any minor and major time units employed within its own timebase.

Advantageously, the signals generated from the said first subsystem can be broadcast asynchronously to all other subsystems. As an alternative, the information can be directed to a specific other subsystem.

Preferably, the signal output from the first said subsystem including the said arbitrary events is arranged such that the shortest time periods are signalled first and the longest period last or, alternatively, vice-versa. This should ideally be a matter of convention for all sub-systems.

Advantageously, the said first subsystem is arranged to transfer at least one time unit, which is advantageously a multiple of the shortest time unit of interest.

Preferably, the method includes the step of providing a time-ordered sequence of timing information for transfer to a respective plurality of further subsystems. Alternatively, the method can be arranged to provide for the multiple generation of the output signal and arbitrary events for transfer to a plurality of further subsystems.

Advantageously, the said second subsystem is arranged to track its own reference timebase by means of a synchronously clocked counter, which is then advantageously arranged to count minor and major units of time.

Preferably the method is arranged such that the calculating scaling factor is arranged to convert any absolute or relative time values so as to send timing information to another subsystem.

Advantageously, the first subsystem's timebase scale of the second subsystems minor time-unit comprises the ratio between the said first subsystem's own timebase measured count for the second sub-system's signal time unit to the second sub-system's declared count for the signal time unit, using its minor time unit.

Thus, as will be appreciated, the method provides for the exchange, preferably through a peer-to-peer connection of information and the calibration of timing signals, during a said set-up phase, that relates to each subsystem's timebase.

According to another aspect of the present invention, there is provided apparatus of a first sub-system arranged for use within a system having first and second sub-systems with different respective clocking domains, the apparatus comprising means for generating a reference output signal including arbitrary events for receipt by the said second subsystem.

According to yet another aspect of the present invention, there is provided apparatus of a second sub-system arranged for use within a system having first and second subsystems with respective different clocking domains, wherein the said second sub-system is arranged to track its own reference timebase, and store its timebase at least once as triggered by arbitrary events within a signal received from the said first sub-system, and which includes means for calculating a scaling factor of the time difference for its own timebase relative to the timebase reported by way of the arbitrary events on the received signal.

Yet further, the present invention provides for apparatus as defined above and in combination.

Preferably, the signal arranged to trigger storage of the timebase noted above comprises the signal generated by the means of generating the reference output signal including the arbitrary events.

As will therefore be appreciated, the present invention provides for a method and related apparatus and system in which at least two subsystems, each operating with different clocking domains, and that are required to operate together with some timing coordination, can achieve, by way of a general mechanism and interface, the establishment of synchronization of one subsystem co-operatively with the other subsystem, and either statically or dynamically. This can allow, for example, an upgrade to new technologies, or change in functionality, while still allowing the other subsystem to re-establish synchronization with it after any such change, and without having also to be upgraded or changed.

Advantages of simplicity and development cost saving are therefore readily achievable.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a schematic block diagram of a peer-to-peer connection of two domains for the transfer of synchronization information according to an embodiment of the present invention; Figs. 2a and 2b are timing diagrams showing signalled and measured timing units arising in accordance with the system of Fig. 1; and Fig. 3 is a schematic block diagram of one of the synchronically clocked domains of Fig. 1.

Turning first to Fig. 1 there is illustrated a system 10 comprising two respective subsystems 12, 14 each comprising respective clocked domains which are typically asynchronous with respect to each other.

Transmission path 16 exists so as to allow for the transfer of a reference signal from domain 12 to domain 14 and, likewise a transmission path 18 exists so as to allow for the transfer of a reference signal from domain 14 to domain 12. Message exchange between the two domains 12, 14 is achieved by way of a message exchange data path 20 and control of both of the domains 12, 14 is achieved via control line 22 from an external supervisory controlling arrangement 24.

According to the illustrated embodiment of the present invention, the interface between the two domains 12, 14 has specific requirements. In particular, a data path is required for allowing communication with the other domain and a common information exchange format is also required to allow for transfer across the interface. Also, transmission of a reference-timing signal from one clocked domain to the other must also be provided for. In the illustrated example in Fig. 1, each of the domains 12, 14 can comprise respective clocking domains of respective radio access technologies in a multi- mode cellular phone handset and between which synchronization is advantageously achieved in a simple and cost-effective manner in accordance with the present invention.

It should of course be appreciated that while the previous description is quite specific to radio, the mechanism is fairly general in the type of systems it can be used in, for example, a distributed real-time computing system, where each subsystem is not a common core design, but across which a time co- ordinated system needs to be implemented by achieving synchronization through the subsystems.

A process of information exchange is first required and this may be carried out once, or repeatedly.

The domains each declare their existence, and provide a list of values Corresponding to any minor and major time units used on their own timebase.

It is assumed that the minor timebase unit is the basis used for all declared values and the declaration can be broadcast asynchronously and without interfering with the processes in the other domain(s), or directed to a specific domain. The exchange is initiated by an entity that is outside the scope of the present invention.

Optionally, other information relating to the operational capabilities and constraints of the domain's system can of course be transferred provided there is an established format for such information to be understood.

Next, the timing reference signals have to be connected between the domains assuming that such connection does not already exist.

Once connected, each domain may show its timing characteristics, by outputting events on these signals, corresponding to the minor and/or major timing units of its own domain. A convention can be advantageously adopted for the order in which each domain signals such times, for instance shortest period first, then increasing duration to longest period last, or alternatively vice versa. While it is considered essential only to transfer one time unit, such at least one unit is preferably a multiple of the shortest time-unit of interest.

Further, the timing of this unit should be resolvable with sufficient accuracy in the domain to which it is being transferred.

It is the responsibility of the two or more connected domains to capture the timing signals from (each of the other domain(s) using its own timebase tracking mechanism, including any resynchronisation that may be necessary.

These measurements allow for calibration of the domains with respect to each other.

In a situation in which more than two domains require exchange of timing information, each domain will have to capture timing from more than one domain. This can either be done by arranging a time-ordered sequence for the domains to show their timing to the other domains, or it can be done by duplicating the mechanism and interfaces supported in each domain for capturing timing from the other domains.

Once each domain has captured the timing of the minor and major units of the one or more other domains, it can start the process of establishing the scaling between each of the other timebases and its own timebase.

It the case that an attempt is made to measure time units of a domain within another domain, but the timing resolution of the measuring domain is not sufficient to resolve one of these units, then the method can be arranged to measure the next longer unit which is the shortest from which the lesser timing unit(s) can be determined, using the count value already declared by the source domain for that unit. It should be noted that the calculation from the longest major unit measured will give the most accurate estimate for the minor time unit of the other domain in the measuring domain's timebase. If required, a statistical approach can also be implemented by multiple measurements of the same interval, providing an average estimate that improves upon a single 1 5 measurement.

For example, in a situation in which: X = Own timebase's scale of other domain's minor time-unit (real number); Y = Own timebase's measured count for other domain's signalled time unit (integer number); and, Z = Other timebase's declared count for the signalled time unit, using it's minor time unit (integer number), It is found that X = YIZ Using the estimate (Y) of the other timebase units, and using the count(s) (Z) declared by that domain for each of its minor and major timing units, then the conversion between own timebase and the measured timebase can be made by determining the scaling factor X from the relationship as outlined above.

Figs. 2a and 2b comprise timing diagrams illustrating the relationship between the minor and major time units of the signalled timing units between the domains.

Fig. 2a illustrates the signal timing units between the domain 12 and domain 14, and Fig. 2b illustrates the measured estimated timing units in the domain 14 having regard to the output from domain 12.

Turning now to Fig. 3, there is illustrated in further detail aspects of the present invention as can be found in either one of the domains 12, 14 illustrated in Fig. 1. For this example however, Fig. 3 is considered to illustrate domain 12.

As can be seen, the domain 12 includes a clock source 26 from which a clocking signal is delivered to a timebase tracker 28 serving as a synchronized counter and from which signals are delivered to a reference signal generator 30, one or more timebase latches 32 and a control and processing element 34.

Each of the reference signal generator 30, the timebase latch 32 and control and processing element 34 connect to the other domain 14 in the system as follows.

Reference signal generator 30, whilst also receiving an output from the control and processing element 34 is arranged to provide the output reference signal on the signal path 16. The timebase latch 32, whilst providing an input signal to the control and processing element 34 is likewise arranged to receive the output reference signal delivered from the domain 14 on the signal line 18.

As illustrated, the control and processing element 34 also provides connectivity to the message exchange data path 20 also illustrated in Fig. 1.

Importantly, functionality of the domain 12 must include the following factors which are described on the basis of a dual domain system.

The ability to track its own reference timebase, for instance using a synchronously clocked counter, counting minor and major units of time.

The ability to generate arbitrary events on its reference output signal and at a frequency at most equivalent to the shortest minor time unit period, and at least equivalent to the longest major time unit period that can be usefully measured by another domain's clock to determine the required accuracy. In practice it is found that this may be a compromise between the time taken to measure the period and the accuracy required.

The ability to store its own timebase, at least once, triggered by consecutive events on the reference signal provided by the output of the other domain is also important along with the ability to calculate time differences between stored values of its own timebase.

The receipt and transmission of information to the other clocked domain, by means of the data path is required as also is the ability to calculate the scaling between time differences in its own domain and that reported by the other domain.

Finally, the conversion by this scaling factor of any absolute or relative time values either to send timing information to the other domain using its timebase, and/or to receive and convert to its own timebase timing information supplied by the other domain using its timebase allows for particular advantages of the invention.

Thus, it will be appreciated that the invention provides for means for achieving synchronization between two relatively un-synchronized clocked domains and in a manner that is readily adaptive to changes in the clocking schemes of one of the domains.

However, it should be noted that the synchronization process would have to be repeated in the case where the clocking system is altered.

Statically, the domain could be substituted with another implementation, perhaps with different functionality, but the general method to establish synchronization could still be achieved with no extra effort, other than that necessary to implement the new system functionality required by the change.

With particular reference to mobile radio communication devices, the standard approach for achieving the appropriate synchronization has to be implemented with specific information about all of the domains, and also requires redesign of all domains when new domains are added, or one of the domains is updated in some manner.

By means of the present invention however, no one domain needs specific prior knowledge about the clock or timebase of any other domain since this is achieved by way of a general purpose process of information exchange after the domains are connected.

Provided all domains of the method and arrangement of the present invention in a consistent manner, it readily becomes available to simplify the connection between arbitrary set of domains without requiring any particular redesign.

It should of course be appreciated that the invention is not restricted to the details of the foregoing embodiment and the invention is readily applicable to any system that includes interacting subsystems operating with different clocking domains.

Claims

1. A method of transferring timing information from a first sub- system to a second sub-system of a system, the first and second sub- systems having different clocking domains and the method comprising the steps of, in the first sub-system generating a reference output signal including arbitrary events, and in the said second sub-system tracking its own reference timebase, storing its own reference time-base at least once and as triggered by the said arbitrary events within the signals from the said first subsystem, calculating time differences between stored values of its own timebase, and calculating a scaling factor of the time difference of its own timebase relative to that reported from the first said sub-system so as to employ said scaling factor for converting time values to achieve synchronization between the said sub- systems.

2. A method as claimed in Claim 1, wherein the arbitrary events are generated at a frequency which is at most equivalent to the shortest minor time unit period that can be usefully measured by a clock of the other subsystem.

3. A method as claimed in Claim 1 or 2, wherein the arbitrary events are generated with a frequency at least equivalent to the longest major time unit period that can be usefully measured by the clock of the other subsystem.

4. A method as claimed in Claim 1, 2 or 3, in which each subsystem is arranged to provide a list of at least values corresponding to any minor and major time units employed within its own timebase.

5. A method as claimed in Claim 1, 2, 3 or 4, wherein the signal output from the first said sub-system including the said arbitrary events is arranged such that the time periods are signalled in an order determined by their lengths.

6. A method as claimed in Claim 1, 2, 3, 4 or 5, wherein the said first subsystem is arranged to transfer at least one time unit, which is a multiple of the shortest time unit.

7. A method as claimed in any one or more of the preceding claims and including the step of providing a time-ordered sequence of timing information for transfer to a respective plurality of further sub-systems.

8. A method as claimed in any one or more of Claims 1 to 6, and including providing for the multiple generation of the output signal and arbitrary events for transfer to a plurality of further sub-systems.

9. A method as claimed in any one or more of the preceding claims wherein the second sub-system is arranged to track its own reference timebase by means of a synchronously clocked counter.

10. A method as claimed in Claim 9, wherein the second sub-system is arranged to count minor and major units of time.

11. A method as claimed in any one or more of the preceding claims in which the scaling factor is arranged to convert absolute or relative time values for the transfer of timing information to another subsystem.

12. A method as claimed in any one or more of the preceding claims in which the scaling factor is arranged to convert absolute or relative time values so as to receive and convert timebase timing information supplied by the said first subsystem using its own timebase.

13. A method as claimed in any one or more of the preceding claims in which the first sub-system's timebase scale of the second sub-system's minor time-unit comprises the ratio between the first sub-system's own timebase measured count for the first sub-system's signal time unit to the second sub-system's declared count for the signal time unit, using its minor time unit.

14. Apparatus of a first sub-system arranged for use within a system having first and second sub-systems with different respective clocking domains, the said apparatus comprising means for generating a reference output signal including arbitrary events for receipt by the said second sub system.

15. Apparatus as claimed in Claim 14 wherein the arbitrary events are generated at a frequency, which is at most equivalent to the shortest minor time unit period that can be usefully measured by a clock of the second sub system.

16. Apparatus as claimed in Claim 14 or 15, wherein the arbitrary events are generated with a frequency at least equivalent to the longest major time unit period that can be usefully measured by the clock of the subsystem.

17. Apparatus as claimed in Claim 14, 15 or 16 and arranged to provide a list of at least values corresponding to any minor and major time units employed within its own timebase.

18. Apparatus as claimed in Claim 14, 15,16 or 17, wherein the signal output from the first said subsystem including the said arbitrary events is arranged such that the time periods are signalled in an order determined by their lengths. I

19. Apparatus of a second sub-system arranged for use within a system having first and the second sub-systems with respective different clocking domains, wherein the said second sub-system is arranged to track its own reference timebase, and store its timebase at least once as triggered by arbitrary events within a signal received from the said first subsystem, and including means for calculating a scaling factor of the time difference for its own timebase relative to the timebase reported by way of the arbitrary events on the received signal.

20. Apparatus as claimed in Claim 19, wherein the said second sub- system is arranged to track its own reference timebase by means of a synchronously clocked counter.

21. Apparatus as claimed in Claim 20 and arranged to count minor and major units of time.

22. Apparatus as claimed in Claim 19, 20 or 21, wherein the scaling factor calculated in accordance with the present invention is arranged to convert any absolute or relative time value so as to receive and convert its own timebase timing information supplied by the said first sub-system using its timebases.

23. Apparatus as claimed in any one or more of Claims 14 to 18 and including a second sub-system as claimed in any one or more of Claims 19 to 22.

24. A method of transferring timing information from a first sub- system to a second sub-system each having different clocking domains and substantially as hereinbefore described with reference to the accompanying drawings.

25. Apparatus for use as a sub-system within a system having first and second sub-systems and substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.