Method and arrangement for correlating time bases between interconnected units   

Abstract: A system and arrangement for correlating time in different time bases used by interconnected units by timestamping a reference event with a time determined with respect to a first time base. A message unit provides the time to a second interconnected unit that uses a second time base. A translation device is configured to calculate a difference between the time measured by the first time base and in the second time base. The difference is used to translate a time measured by the first clock to a time in a different time base at run time.

The present application is a continuation application of U.S. patent application Ser. No. 11/554,370 filed Oct. 30, 2006, the contents of which are hereby incorporated by reference into this application, which is a continuation under 35 U.S.C. 120 of International Application PCT/SE2005/000581 filed on Apr. 21, 2005, the contents of which are hereby incorporated by reference into this application, which claims priority to Swedish Application 0401130-0 filed on Apr. 30, 2004.

The present disclosure relates to a fixed and/or movable system, in particular in or for vehicles, for example cars. The system operates with common or related time bases for indication of the time of detected or generated events in the system, and/or in a system or systems connected to this.

The present disclosure also relates to a device for effecting the establishment of functions carried out by two or more units (nodes) comprised in the system in a fixed and/or movable system, in particular in or for vehicles, for example cars. The device can relate to arrangements for detection, control, analysis and/or simulation of comprised units.

The use of systems of this type in, for example, vehicles, is already known and reference can accordingly be made, among other things, to the patent applications and patents submitted by and granted to the same applicant as the present applicant. In the respective systems, the message and information (data) transmissions are carried out using or in accordance with protocols of a known type, which can be of a standardized type, for example Universal Serial Bus (USB), Controller Area Network (CAN), Local Interconnect Network (LIN), Ethernet, IEEE 802.11x, Infrared (IR), Wireless USB (WUSB), etc.

With this type of system, there are problems in determining events and/or time functions without relatively complicated and bandwidth-intensive arrangements. There is, for example, a desire to be able to determine the occurrence of the events and/or give indications of the time so that the normal traffic can be utilized to indicate the relevant time and/or occurrence of the event, for example, without extra hardware needing to be involved. The object of the disclosure is, among other things, to solve this problem. There is a need, in the respective module units, to be able to operate with preferably small resources with the object of simplifying the construction of the units. There should also be great freedom of choice in the construction of systems and their relationships. This disclosure also solves this problem.

A major problem in distributed embedded control system is to synchronize the generation of events in different nodes to each other in a timely manner, e.g., reading sensor values, execution of movements, releasing of power etc. The main solution to this problem is to create a global time and synchronize clocks at each node. Usually the time synchronization is made at the communication level. Typical examples are TTCAN, TTP and FlexRay protocols in the vehicle industry and SERCOS in the factory automation industry. All of these communication protocols are time triggered and it is a common opinion that safety critical distributed embedded control systems have to be based on a time triggered communication. An alternative to synchronizing clocks is to have each module relying on its own local clock and have a time translator recalculating the time of each clock to a common global time, but it has been regarded impossible to do in real time.

U.S. Pat. No. 5,896,524 suggests a method to recalculate clock readings by associating event pairs related to each other. However, such conventional methods cannot be used in realtime (e.g., see column 1, line 65 through column 2, line 4). What is needed is a method and apparatus that calculates the relationship between local clocks at run time. What is further needed is to calculate the relationship between local clocks and a global time base at run time.

U.S. Patent Application Publication US2006-0143345A1 shows that, in realtime systems at run time, it is more efficient to use different time domains within the system, wherein each time domain is created according to the need of cooperating nodes, rather than to rely on a global time. However, a global time may be better used for analyzing a system.

Each system in which the disclosure can be used can be regarded as individual, one or more series or sequences of events that are related to each other in time and space. There can be different time descriptions and time frames within one and the same system. Smaller systems can be comprised in the system, which in turn can, now or later, be comprised in other systems. During the first stage, the “drawing board” stage, of a system development, it is expedient to relate all the events to one and the same time frame, for example related to the physically defined second. The degree of coordination that is required of the different events in order for the required system function to be achieved can be analyzed in a first stage. In a second stage, an analysis of the relationship of the individual events to each other can indicate that other time frames and the utilization of knowledge concerning the association of different events to each other can simplify the design of the final system and the description, verification and validation of the same. The disclosure simplifies these development processes.

For analysis or verification of systems, there is a need not only to timestamp events that have occurred, but also to know with what precision and/or accuracy the timestamping is carried out.

It can happen in systems that different parts of the system relate events to different time bases, which in turn are related to each other.

Analysis and monitoring instruments of different types for vehicles are often based on standard computers with operating systems, for example a personal computer (PC) with WINDOWS XP®. The operating system (OS) simplifies the development of the software at the price of precision of timestamping of external events. Therefore special units are introduced between the PC and the bus system that, among other things, comprise a clock for timestamping of incoming time messages. For example, with the utilization of the program CANANALYZER from the company VECTOR, a CANCARDXL from the same company is connected to the PC. The CANCARDXL has a local clock and can timestamp messages from two CAN busses. If there is a need for several CAN busses, an additional CANCARDXL unit must be connected to the PC and the two CANCARDXL units must be connected to a coordination unit via a coaxial cable arrangement in order to synchronize their local clocks to a common time. By utilizing the disclosure, timestamping can be carried out with great precision, utilizing only components to be found as standard in the PC.

SUMMARY

This disclosure addresses time synchronization in distributed embedded control systems by selecting specific events and their relation to the local time at different nodes ahead of time to be identified as reference events. A time translator can then filter out messages with time stamps related to the reference events, and a respective transmitting node within the system. By defining the relationship between a reference event, time-stamped according to a first clock at a first node, and the time relation of the reference event to a second clock, the time translator can recalculate the first time to the second time and vice versa at run time, i.e., in real time.

In addition, a reference event can generate several secondary events. By defining the relationship between such a reference event, its secondary events, the time stamping of these events, and how these time stamps are transmitted to a time translator, a time translator can be programmed to recalculate the time at one time domain to the time at another time domain at run time

An occurrence of the execution of a function can be arranged to be able to be detected and determined by means of one or more devices that perceive time, for example clocks, and/or devices that indicate events, which devices are comprised in one or more of the units that constitute or form module units in the system. The system can thereby include one or more serial, distributed and protocol-utilizing systems. The respective determination is to be arranged to form the basis of or invoke functionality in the system and/or in monitoring, analyzing, verifying, completely or partially simulating or stimulating devices in the system.

A consequence of the concept of the disclosure is that the same or different events that are perceived or generated by different modules in the same or different systems can be time related in a simple way. The modules that are affected by the time relating can perceive certain events at the same time, or alternatively certain different events for which the time relationship is known. Such events belong to the group “reference events”. The modules can be arranged to generate or detect reference events, display local clock function, be able to read off local time upon the detection or generation of a reference event and provide time information on the basis of the value that was read off being sent to one or more translation units. The translation unit(s) then utilize these values in order to create a common time reference for the modules and events concerned, with the result that it is possible to create time indications that are comparable. The translation unit can be considered to create a common time domain for relating events. Comparisons can be carried out in different time domains that can be created by different translation units, which can utilize common reference events. In an embodiment, the bit pattern in a communication protocol is utilized as reference event. For example, the Start Of Frame bit (SOF) in CAN is suitable. More specifically, the sampling point in the bit can be used, as certain CAN controllers, for example MCP 2515 from MICROCHIP (Microchip Technology, Inc., 2355 West Chandler Boulevard, Chandler, Ariz., USA, 85224-6199), generate a signal for this that can be used in order to trigger the requisite electronics for the reading off of local time for the occurrence of the event.

Further developments of the concept of the disclosure are apparent from the following.

For example, the system operates with event functions and accordingly reference events can be utilized which can be related to one or more reference event generators. A reference event can be sent from a common point and can refer to a common group. The reference events can occur at particular intervals and can themselves define the clock function (compare with a Phase Locked Loop). The reference event detectors must be able to be placed in the units and accordingly a detector can be placed in each unit. An interrupt generated by a selected protocol\'s communication circuit can be utilized as a detector. The respective detector can be set up by defining or implementing how it is to be obtained (for example, by connecting to a suitable layer in the protocol stack and searching there for a special packet/bit pattern/edge). Events must be able to be related by group, for example with regard to sequence or time. The group can work with a common starting point. Thus, for example, a unit can communicate directly with all units in the group or at least send messages that all the other units can detect. The messages can represent typical events. The respective message can, for example, include packets according to any serial communication standard, for example the protocols mentioned in the introduction. The reference event can consist wholly or partially of a message. The USB protocol\'s Start-of-Frame (SOF) packet can advantageously be selected as reference event. This packet is transmitted in the normal way and has a sequence number, which facilitates the correct association of timestamp to reference event. USB packets propagate in a USB system in a defined way and a USB host can be regarded as a reference event generator in its own time domain, distinct from other time domains, for example the domain in which a WINDOWS application operates, in the same PC as the USB host. The reference events can be transmitted to all units that are comprised in the same USB arrangement, that is all units can listen to the same event, for example, at the same time. The phrase at the same time here means a maximum of 50-100 ns jitter in the detection for all the units plus up to a couple of hundred ns constant delays. A USB Hi-speed maximal delay can be 26 ns in the cable, 4 ns in the “hub trace”, 36 hs-bits in the hub electronics in a maximum of 5 levels plus 30 ns for connecting in last unit, totaling 530 ns. A Hi-speed jitter due to the USB protocol can be a maximum of 5 hs-bits per hub and a maximum of 5 hubs can be connected, which gives a maximal uncertainty of 25 hs-bits, which corresponds to approximately 50 ns time inaccuracy for the propagation of an SOF through a USB connection. A “hs-bit” is here considered to be the duration of a hi-speed USB bit time i.e. 1/(480 MHz), or approximately 2 ns.

In the embodiments, each unit can comprise a local clock which is able to be read by or in the application in question. Timestamping can be carried out of each reference event and the timestamping is carried out preferably with externally triggered capture register. Correct association of the timestamp with the reference event can be ensured. The timestamps can form the basis for relating clocks, time and events. The clocks or the read-off time must be able to be related. In addition, in an embodiment, a time master can be included, whose time is, if required, to be regarded as global (in groups). In order to create a transitive relationship, that is even if two different units cannot directly relate their time to each other, this can still be achieved if both can relate their times to a utilized master or intermediate unit. The time master can, in turn, be synchronized or related to a second reference, for example GPS. This gives the system access to a correct physical second that can be used for physical calculations, for example engine speed, power, accelerations, etc. The location of the time master can be in a common point in the system concerned, can be separate or can have another role in another unit. The role or the function can be changed. In an embodiment, the system does not need to utilize any master unit, but instead the translation takes place in an all-to-all function. In addition, it should be pointed out that a time master does not need to have its own physical clock, but instead can construct a virtual clock function by utilizing timestamps of reference events carried out by and messages from modules with their own time domains, that are connected to the system. With knowledge of the relationships of the reference events and respective time domains to each other, the time master can transform the time information to a time domain of its own and give respective time information referring to its own time domain to other units within or outside the system.

An important part for an efficient utilization of the disclosure is the actual development process for the device. In a first stage, the events are identified that are to be generated and detected and their relationships to a common notional time base relating to times and a permitted range around these, in order for the device to have the required functionality. In a second stage, events are identified that can constitute reference points between different units, in order for these to be able to detect, initiate or generate other events within the required time range, relative or absolute. In a third stage, functions are implemented in an actual design in order to achieve the required functionality. It should be pointed out that reference events are defined at system level and that these do not need to be known at module level. A basic idea in the disclosure is the concept of time. Each interaction between given event patterns can be regarded as having its own time domain, that is the time frame is based on its own time tick generator (which can be linear or non-linear) and the time indication is given as the number of ticks, whole plus if required parts thereof, according to a linear or circular model. The different time domains can be transformed from and to each other. Domains with circular model will appear as a cyclic course of events and those with a linear restricted model as discrete intervals in a linear unrestricted model. For general analysis tools, it is expedient to utilize a linear unrestricted model with the physical second as time tick. Another basic idea in the disclosure is the concept of a system. According to the disclosure, the system is regarded as a number of event functions that are coordinated by a controlling unit, the sum of all the event functions. These functions can be of two types, event-generating or event-detecting. The coordination takes place in time and space. A part of the coordination is carried out mechanically, and a part is carried out through the exchange of information between electronic units, of which a part of the latter is carried out via serial communication, for example of the CAN or USB type, directly or in combination. The system S is described with the number n of subsidiary functions F as:

S = ∑ 1 n  F i ,

where Fi is the sum of the number m of events h, that is

F i = ∑ 1 m  h j

In the first stage, the system in one or a few time domains is described, which system is well suited for describing and calculating its characteristics, for example the time domain T. This can be represented symbolically by:

S  ( T ) = ∑ 1 n  F i  ( T ) F i  ( T ) = ∑ 1 m  h j  ( T )

In the second stage, a number of events are identified that are mutually interconnected between functions of interest and which are suitable for providing a time domain for the functions. These events are designated reference events. It is often expedient to have non-linear time ticks in time domains for event functions that are mechanically connected. In addition, reference events are identified that are connected in chains, that can be described mathematically, to different time domains. Starting from a generated event in a time domain, the detection of which generates a further event (in the same or another time domain), which in turn is detected in another time domain, during the development work a mathematical transfer function can be created between two time domains similar to a transformation of one coordinate system to another. Such transfer functions are implemented as required in the system\'s different units. The system can be described symbolically as follows:

S=ΣFi(Tq Tk, . . . )

T1=∀Tm, where ∀ is a transfer/reproduction operator between the time domains 1 and m.

In an additional embodiment, one or more time coordinators can be utilized. These can delegate any role as time master and receive and send timestamps of reference events. In this connection, the transmission can be carried out to any translation units in order for these to be able to calculate and translate the time in question. In an additional embodiment, certain units carry out the actual translation function in question. The time coordinates can receive and send other timestamps to any translation units. In an embodiment of the disclosure, the time coordinator is arranged in a common point in the system in question. The disclosure also takes into account the need for time translators to be included. Time translators handle the translation of time for the units that do not carry out the translation themselves.

A time translator can be located anywhere in the system, but a location in a common point is advantageous from the point of view of efficiency. A time translator can carry out translation from one unit to another via a selected reference time or alternatively according to the all-to-all principle, that is directly from each unit to every other unit. In this connection, a logical translation matrix can be utilized. A matrix that can keep track of how translation is to be carried out rapidly from all-to-all can, however, assume large dimensions and require substantial resources to keep updated (the complexity scales quadratically), but gives as a result faster translations. It is also possible to carry out the time translation just by keeping the reference timestamps updated, but this results in more work per translation. The translation unit can keep statistics of how well the clocks are related and can send the measurement value together with this information as a parameter. The inaccuracy can be calculated and sent with each measurement value. The translation function can be carried out with greater accuracy afterwards, that is when an additional reference message has been exchanged.

In connection with this, the derivative for the current period can, for example, be used instead of assuming that the same derivative applies as in the preceding period. Expressed in more general terms, interpolation is used instead of extrapolation for indication of a value. This is of particularly great significance for analysis and verification of a system\'s function. In short, it can be said that each unit/module that has been given access to the occurrence of reference events in different time domains can be arranged to carry out translation between the time domains, irrespective of whether the units/modules themselves are comprised in or represent any of the domains or not. In order that no ambivalences shall arise concerning the time domain to which a particular indication belongs, protocols should be set up which, for example, state who translates what and to what extent a unit\'s incoming/outgoing indications are to be considered to belong to the time domain of the transmitting and/or receiving unit.

The further developments can comprise the system\'s units being physically synchronized to their local clocks in accordance with some master time. This in itself increases and complicates the hardware in the units, which in such a case must perhaps still be supported by software resources. All clock operation can be carried out proactively, that is once the clock is to be used, it already shows the time in the master\'s time domain and it has only to read this off, which can reduce the unit\'s response time and in this way justify the greater complexity. The respective unit can itself calculate how it is to regulate its clock using the master\'s timestamps of the reference events. The respective unit can let the coordinator or translation unit calculate how the regulation and offset compensation are to be carried out by sending their timestamps of the reference events to the same and then awaiting a response.

The units can translate their time to another time before the time in question is transmitted. This does not need to require any extra hardware, but instead can comprise some software resources, depending upon how the translation is to be carried out. The translation work is carried out between production and consumption of the value. The unit can itself calculate how the translation is to be carried out using the master\'s timestamps of the reference events. The unit can let the coordinator/translator calculate how the translation is to be carried out by sending its timestamps of reference events to the same and then awaiting a response. The units need not be aware of another time than their own as far as the time relationship is concerned. It is sufficient for the units to send their respective timestamps of reference events to the coordinator. This requires relatively little resource in the units. The translator is responsible for all translation/time relating. The translator is arranged with compute power appropriate for the translation method.

Depending upon what precision is required for the detection of a reference event within a system, a group of individual events can be regarded as one and the same reference event. For example, SOF in CAN messages can be utilized as a reference event. A practical way of detecting SOF in CAN is to utilize the sampling point in the CAN controller. As the detection of SOF in the respective node is dependent upon the setting of the sampling point (which can be different in different nodes) and the nodes\' distance to the transmitting module, the time of the detection will vary depending upon which node is transmitting and the setting of the receiving module. If SOF of any message is used as a reference event, in practice it is a group of events that is utilized.

The precision of the reference event is obviously not sufficient to measure, for example, the delay between different messages from different nodes. This is possible if instead individual CAN messages are selected as reference events (if SOF is to constitute a reference point, the message may not, except in certain special circumstances, have won the bit arbitration from a message with lower priority). More precisely, it can be the occurrence of specific edges/bits in the different nodes that gives the ability to determine delays between units, and the fact that these edges/bits have been propagated in both directions relative to the delay that is to be determined. Consequently, specific edges/bits that have been propagated through the system as undisturbed as possible are suitably selected for determining delays. An edge/bit that very probably originates from only one transmitting unit can be one following the arbitration field in a CAN message (however, suitably not the ACK bit, that is transmitted by receiving units).

At the system level, it is known which CAN messages the respective nodes transmit. By each of the transmitting and receiving modules timestamping one and the same message, and messages being sent in both directions through the system, the delays between respective modules can be measured and calculated to a common time domain.

In one embodiment, a unit, for example any such unit, can act as time master (with or without its knowledge). The units can work with a translation function for each time that is to be translated/related to the master time. The translation work is carried out between production and consumption of the value. This can result in a delay of possible consumption of the same.

The translation function can be carried out by the offset between the first and second times being added to the time that is to be translated. With this method, little compute power is needed for the respective translation. Synchronization/time relating is preferably carried out frequently with this method in order to minimize the effect of the respective clock\'s drift in relation to the other clocks. The translation can also be achieved by both offset and fixed frequency error compensation (drift compensation). The translation Ax to Bx (new and old refer to reference timestamps) can be carried out as follows:

Bx=Bnew+(Bnew−Bold)*(Ax−Anew)/(Anew−Aold)

Given a computer with limited resolution and/or calculation accuracy and given that the times A and B are already scaled to be approximately equal (the derivative between them is approximately one), the following method can give a better result:

Bx=Bnew−(Ax−Anew)+(((Bnew−Anew)−(Bold−Aold))*(Ax−Anew))/(Anew−Aold).

Viewed analytically, the two methods are equivalent and are based on linear regression. As the calculation is carried out using a computer, discrete values must be used which results in limited possibilities for representation which has the result that the sequence is important. Irrespective of the method, care must be taken that the calculation does not overflow or get truncated in an undesirable way. The latter method can be a way to make this easier.

There can thus be great computing power per translation but, in return, the time relating does not need to be carried out as often in order to attain the same precision. The constant frequency error can be determined offline or the frequency error can be measured online. There can also be cable delays of a not inconsiderable size, which must then be included in the calculation. In one embodiment, negligible cable delays are selected. In the offline case, offset and/or frequency deviation can be measured once and for all and appropriate constant values can be calculated and inserted in the translation function.

In one embodiment, where delays can be measured online, units can be arranged so that reference function executions propagate through the communication medium in both directions relative to the units whose delay is to be measured, during which the two units determine the occurrence of the reference function executions relative to some time. These determined occurrences can be used to determine the delay.

The translator can save information in the respective unit about how the clock behaved during the most recent session in order to be able to phase in the unit in the next function stage more quickly and/or make the synchronization/time relating easier for the translator.

The more of the abovementioned resources, methods and/or functions that can be made dedicated, the more easily predicted and/or easily used and hence perhaps also more reliable is the utilization of clocks, time, time synchronization and/or time relating in the system.

The system described can advantageously be used on a vehicle, for example a car, lorry, tractor, scooter, boat, ship, airplane, etc. For the direct control system in a car, it is advantageous to have time domains with varying time tick in order to coordinate movements that are associated with the mechanical function of the driveline. As each so-called ECU (Electronic Control Unit) comprises a CPU that is controlled by an oscillating circuit that is independent of the movement of the mechanics, an ECU has at least two time domains with associated transformation operator. One and the same ECU can interact with several other ECUs that form groups working in a time domain common to the respective group.

The whole system in a car (vehicle) can have a linear finite time domain, which, for example, starts with the ignition key\'s “on” position and which ends with the ignition key\'s “off” position. In this time domain, the system behaves in a way expedient for driving the vehicle. When the ignition key is in the “off” position, the system operates in a different time domain, for example a circular time where information is obtained from some operating module that periodically listens for commands from a wireless signal for opening or locking of the car\'s doors and/or control of alarm functions. The car can be comprised in other systems connected with traffic control, traffic monitoring, law-enforcement monitoring, etc., which make completely different demands, but which now and then interact with the car\'s direct control systems.

Here, other time domains can be better suited, for example a time domain where the time tick varies with the location of the car. In a monitoring system, a need to update the car\'s location can be lower when it is in the country in normal circumstances than within built-up areas or in the vicinity of an accident. This frees bandwidth requirements in both the car\'s control system and the monitoring system. The present disclosure has a great advantage in that the development of systems that are to be incorporated in larger systems at a later date can be carried out without advance planning. When the systems are to be incorporated, the respective systems\' event-generating and event-detecting functions are reviewed. As the respective systems have many such functions, there is a great probability that events will be found that can be utilized as reference events for the coordination of the systems that is required in order to obtain the required result. If suitable events cannot be detected during the coordination analysis, expedient or suitable event-generating or event-detecting functions can be created and introduced into any one or both systems.

BRIEF DESCRIPTION OF THE DRAWINGS

A currently proposed embodiment of a device that has the significant characteristics of the disclosure will be described below with reference to the attached drawings in which:

FIG. 1 shows a schematic illustration at system level of how various comprised module units and systems are logically interconnected,

FIG. 2 shows in detail a unit 103 comprised in FIG. 1,

FIG. 3 shows a simple schematic illustration of a subunit 105 or 350 shown in FIG. 1,

FIG. 4 shows a schematic illustration of a first unit 104 comprised in FIG. 1,

FIG. 5 shows two possible ways of measuring delays between units,

FIG. 6 shows how the USB protocol\'s SOF packets can be utilized for time relating in a system with a computer, for example a PC, and a number of units connected to this,

FIG. 7 shows a traffic system in which the cars utilize local independent time domains that are coordinated with a traffic monitoring system with centrally coordinated, flexible time domains, and

FIG. 8 shows schematically a traffic monitoring system.

DETAILED DESCRIPTION

In FIG. 1, three different systems are symbolized by S1, S2 and S3 interconnected to a system S. The systems can be of the types described in the introduction, for example USB, CAN, Bluetooth, etc. The serial bus connections in the systems are indicated by B1, B2 and B3. The systems work with protocols P1, P2 and P3 associated with the standards. In the systems there are one or more first units 104, 104′, 104″. In accordance with the disclosure, function events or function executions in the systems are to be related with regard to some type of time, for example linear time, circular time, virtual time, etc. The empty boxes in FIG. 1 illustrate other modules connected to their respective bus and which could each contain a microcontroller and related clock used, for example, to read sensor values, control mechanical actuators, or to control electrical devices.

The systems work with a number of functions. Any first function is indicated by F1 and relates to one or more reference times or master times to which the first units can relate. The times in question can be, for example, real and/or virtual. The time that any clock function 352, 410, 457 (not indicated in FIG. 1) represents can constitute an example of a real time, which can be with or without the knowledge of the unit. An example of a virtual time is an average time extrapolated from suitable units\' time.

The systems can also comprise one or more second functions F2 that represent translation functions between different times in the system. Depending upon the characteristics of the times, a suitable method is selected for determining the translation functions. If, for example, two times both represent linear/modular times with tick of the same size, linear regression of the type is advantageously used.

A third function is indicated by F3 and is arranged to generate/represent the reference function execution that can at least be detected by the units that must be able to be related directly. This function can either be arranged in one or more dedicated new units and/or in any one or more existing units. As a proposal, suitable existing function executions in the system are identified and arranged to carry out the function. Examples of such suitable existing function executions in a USB system are SOF packets, which, in addition, are provided with sequence numbers which make easier the correct identification of specific packets. A proposed existing function execution in a CAN system that could be suitable for the disclosure is the SOF bit or suitable edge/bit inside a message and then preferably an edge/bit that occurs after the identification field, but before the ACK bit. In the case when an edge/bit within the data field constitutes F3, the transmitting unit\'s Time Reference (Tref) should, in addition, be able to be sent as data in the same packet in order to save time and bandwidth. In order to make the system more stable, an edge/bit in a message should not be accepted for reference function execution before the whole message has been validated.

The first function F1 can, in principle, be arranged to be in any of the units, with or without their knowledge. The second function F2 must, however, know which unit or units represent the first function F1, assuming that F2 wants to utilize F1 in question. The second function F2 can be arranged in one or more of the units. In this case, the units can be arranged to carry out translations from or to their own times. Alternatively, a unit in question can let any other unit carry out the translation in question. The first function F1 can, in turn, be synchronized with or related to another time, for example UTC and the physical second via GPS, 107. Protocols can be established for how times are to be interpreted and/or translated. If, for example, a group of units is arranged to be able to translate times between themselves, incoming times are selected, for example, that are already translated, while times that are to be sent are first translated to the receiving unit\'s time or vice versa. Alternatively, as described, F1 can be utilized in the form of both incoming and outgoing times being interpreted as or translated to the first function F1.

In one embodiment, a second unit 102 can advantageously be arranged with the first function F1, the second function F2, the third function F3, the fourth function F4, the fifth function F5 and/or a subunit 105. Such an arrangement is particularly advantageous if the protocol P2 consists of USB. In this case, unit 103 should be able to correspond to a unit 200, as shown in FIG. 2, which contains one or more units 201, where 201 can be internal and/or external USB hubs and/or units such as unit 450 in FIG. 4. In one embodiment, the second function may include use of a centralized translator, which means that the first units should be able be implemented relatively easily. A decentralization of the translation function, on the other hand, causes a somewhat higher complexity of the first units, but in return the bandwidth can perhaps be lower and fewer units can be utilized in the system, while at the same time the reliability can increase as the resources are dispersed and accordingly no “single point of failure” needs to be introduced.

FIG. 3 also shows a fourth function F4 that detects the function execution that the third function F3 generates. The first units 104 in FIG. 1 are arranged with one or more subunits 105. FIG. 3 shows a simple schematic drawing of unit 104 where unit 300 corresponds to 104 and unit 350 corresponds to 105. The subunits 350 comprise one or more time-perceiving devices 352, function execution detectors F4, and subunits or capture registers 351 arranged to store times. In the event of an actual detection, the clock 352 is read off and saved in a subunit 351 that saves the reference times in question, here designated Tref. The latter timestamping or reading off can be transmitted to units carrying out the second function F2, which for this purpose are arranged to determine how the translation in question is to be carried out. If the second function F2 is a part of the unit itself, one or more Trefs are awaited from other unit or units, which can be used for determining how translation to/from this and/or other units is to be arranged to be carried out. Alternatively, a unit\'s incoming Trefs can be selected in order to synchronize the local clock to, for example, any F1 on the basis of one or more timestamp(s). The Tref values can be considered to form the basis for relating all time in the systems. This applies irrespective of whether it is a question of translating time locally, synchronizing the time in question locally, or leaving the translation to some other unit. As shown in FIG. 3, any of the functions/roles can be arranged in the unit 300.

One embodiment of the clock function 352 and the subunits 351 is to utilize a counter/timer in a suitable CPU and allowing a detection in F4 trigger a reading off of the counter/timer 352 to capture register 351. The clocks are, in other respects, intended to define system times and can be read off by applications that are executing in the units, in contrast to the clocks that are hidden from the applications such as are often used in certain time-controlled communication protocols. An extremely advantageous facility that the disclosure provides is that clocks can be made as accurate as their applications require, without forcing other clocks in the system to be equally accurate.

An advantageous accuracy can be obtained if the first units\' times are translated directly to each other instead of carrying out the translation via one or more first functions F1. More precisely, it can be said that negative effects originating from, for example, reading off errors and jitter in system components\' electronics and logic can be limited. If, however, it is desired to have all events in the system on a common time axis or basis, for example for analysis, it is advantageous to utilize a first function F1 and plot the events concerned along the time axis that F1 describes. A fifth function F5, shown in FIGS. 1 and 3, includes a coordinator function which receives and sends reference timestamps to a unit that requesting the timestamps concerned, or to all the units that operate with function F2. The fifth function F5 suitably determines, with or without guidance from one or more second functions F2, which unit or units are to operate as or have the role of F1. The second functions in the system or the systems should, in addition, be able to calculate and send/associate translation accuracy/inaccuracy and/or stability/instability of the times/clocks/translations. This is in order not to need to assume that the worst case always applies, but instead to be able to utilize current assumptions.

In the most general case, the units do not need to know the originator of a specific reference function execution. If the units, however, are arranged to be able to measure any delay over the serial communication between two units, they may, however, be provided with this facility. The delay can, for example, be determined with knowledge of a number of occurrences of reference function executions that propagate in both directions relative to the units between which the delay is to be determined. FIG. 5 shows examples of how this can be carried out.

If unit 102 is, for example, a computer of the PC type with an operating system such as, for example, WINDOWS XP, the functions F1, F2 and/or F5 may be able to be implemented in the software that communicates with the OS\'s interface to the communication channel. The advantage of this is that PC computers are very common today and often are already used in many planned target systems and, in addition, usually have resources that can advantageously be utilized. Depending upon the implementation method and system requirements, great care must be taken so that calculations are carried out with sufficiently short response times, irrespective of what the OS is otherwise engaged in. This embodiment can provide a simple, flexible and accordingly cost-effective way of, for example, connecting a computer by means of the hardware to several CAN systems for analysis and/or interaction and, at the same time, provide a competent way of relating time within and/or between the systems. FIG. 6 shows examples of how this can be carried out.

FIG. 4 shows in greater detail than in FIG. 3 a schematic construction of a unit 104 according to FIG. 1, here designated 400. For the sake of clarity, it is provided with two microprocessors, but the task can be carried out by one microprocessor. The unit 400 is connected on one side to a system 401 via the connectors 402, 403 and the connection cable 404. Via the interface electronics 405, the signals on the bus can be read by the microprocessor 406. Using instructions stored in the memory 407, the signals can be interpreted in accordance with the protocol 408 used in the system. In its simplest form, the interpretation can mean that only the received bit pattern is transferred, but the interpretation can be of a more complex type where much supplementary information provided by the protocol\'s rules is added by the microprocessor. Application software, that is instructions for one or more applications that process information available to the microprocessor, is also stored in the memory 407. The information thus interpreted is transferred to the dual-ported memory 409. Additional information of interest can be added to the interpreted information, for example timestamping when the information was obtained from the system. The time is obtained from the clock 410 which is triggered to be read off in a suitable way by the interface electronics 405, 414, 419 or alternatively by function execution detectors 424, 426, 428, for example when reception of a message commences. In order to make the reading off of the clock more independent of the processor 406, the event can be stored temporarily in capture registers 425, 427 and/or 429. The information is stored in the dual-ported memory in an organized way in accordance with rules depending on the system protocol\'s requirements, so that specific information is stored in a specific location indicated by the table 411. The dual-ported memory 409 can be read by the microprocessor 412 which can communicate, according to a second protocol, using rules stored in the memory 413, and physically via the interface electronics 414, with a second system 415 via the connectors 416 and 417. Rules are also stored in the memory 413 for how the information stored in 409 according to the rules in 407 and 411 is converted according to the rules for the second protocol 418. In simpler systems, the second protocol can be based on CAN and several units 400′, 400″, etc., of the type 400. In the same way as described above, the unit 400 also contains rules for a third protocol with the interface unit 419 and connectors 420 and 421 which connect to the link 422 with the protocol 423. A suitable protocol can be based on USB.

In order to be able to synchronize a local clock 410 to an external time, for example, any F1, the processor should at least be able to set a new value in the clock. For the sake of simplicity and reliability, the interface between the clock and CPU should, however, allow the processor to, for example, ask the clock itself to compensate for a given offset and/or frequency error in a way that is acceptable to the unit and the system.

As the ability to get WINDOWS to carry out tasks in real time is greatly limited, it can be advantageous to let second unit 102 include a separate computer system with an OS better suited for the task. Such a computer system can be a unit or module 450 according to FIG. 4 with a microprocessor and peripherals specially adapted to handle communication and calculation problems. A number of modules such as unit or module 400 can be connected to the unit 450 via a suitable connection, for example a USB connection. Such an arrangement has many advantages. The analog and strictly real-time problems are solved by the module 400, while the calculation-intensive and less real-time-critical tasks are handled by the unit 450. The module 450 is connected directly to one or more modules 400 by connectors that are illustrated by 451, 452, 451′, 452′, etc. Communication circuits 453, 453′ are connected to a microprocessor 454 with associated peripherals, among other things memory or memories. These memories contain applications software, that is instructions for one or more applications that process information available to the microprocessor. A memory card 455 is arranged for log equipment, recording and playback capability, etc. A memory 456 connected to the microprocessor can be written to and read from in two (both) directions, that is from both the system side and the tool side. The memory can be divided into a number of subsidiary memories with different algorithms 456′. The clock 457 can be synchronized with or related to the clock in the first unit 410 via the protocol in the abovementioned way. To assist with this, there can be a function execution detector 463 and capture register 464 arranged in a similar way to components in the unit 400.

In this way, all first units 104 connected to a second unit 102 can be time synchronized or time related. In the same way, second units 102 should be able to relate time between themselves. Through time synchronization of the different units, the execution of the applications in the different units can be synchronized or related to each other. Execution of applications or parts of applications that are responsible for measuring can, in this way, be coordinated with execution of applications or parts of applications that are responsible for communication within and between the different units. This means, among other things, that messages sent according to an event-controlled protocol, for example CAN, can appear in a time-controlled way, as applications for the transmission of messages are executed and coordinated in time.

As a result of the execution of applications for measurements being coordinated with the transmission of measurement results, a time relationship is obtained between the measurement and the distribution of the measurement results in the system in the form of messages. The same can, of course, be carried out for indicated events and messages with information about the respective events. Together with the unit 400 and also with suitable software, the unit 450 can simulate completely or partially an ECU in an ordinary CAN system in a vehicle. The unit 450 can be equipped with means for communication with other network protocols, for example Bluetooth 459 and TCP/IP 460 for communication between a network of units 450 and/or tool units implemented in a PC or PDA. As an alternative to storage disks so-called “USB mass storage devices” can be connected to a USB connection. For communication over a telecommunications network, the unit can be equipped with a GSM module 461 and for time synchronization or clock synchronization with a GPS module 462 which can also be utilized for position determination. See above, regarding the protocols.

Irrespective of whether the unit 102 includes a normal PC or a unit such as 450, it can advantageously carry out the function F3, in particular if the selected protocol is USB and the unit is a USB host, which means that the unit generates SOF packets. As mentioned above, these are suited for carrying out reference function executions.

FIG. 5 shows the measuring of communication delays between units, where the units 501 and 502 can be of the type, for example, such as unit 400. In the first case, unit 501 sends a message 503 to unit 502 and both timestamp the message with their local clock. We can call 501\'s timestamp of 503 Tref13, and 502\'s timestamp of 503 Tref23. Thereafter, 502 sends a message 504 to 501 which is timestamped by the two units. 501\'s timestamp of 504 can be called Tref14 and 502\'s timestamp of the same can be called Tref24. If, for example, 502 thereafter sends Tref23 and Tref24 to unit 501, 501 can determine the communication delay, Tλ=Tλ501+Tλgem+Tλ502, between 501 and 502, for example using the following method:

  { T λ = T λ501 + T λ

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