US 8065052 B2
A method 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.
1. A method comprising:
timestamping a reference event with a reference time determined with respect to a first clock operating in a first time base used by a first interconnected unit, the first clock receives a time tick generated in response to movement of a part in a machine;
providing the reference time to a second interconnected unit;
determining a method of correlation between the reference time in the first time base and a reference time in a second time base, the method of correlation being selected from a set of at least two methods of correlation and being selected dependent on at least one of a linearity of the two time bases or a similarity of size of time ticks of between the first time base and the second time base; and
using the correlation to translate a time measured by the first clock to a time in a different time base during run time.
2. The method of
receiving a message at the first interconnected unit from the second interconnected unit; and
accounting for delays within the first and second interconnected units and for a propagation delay between the first and second interconnected units based on the received message.
3. The method of
4. The method of
5. The method of
6. The method of
7. The method of
receiving a global time at the first interconnected unit; and
correlating a time determined with respect to the first clock with the global time.
8. The method of
9. The method of
10. The method of
11. A method comprising:
times tamping a first reference event with a first reference time determined with respect to a first clock used by a first interconnected unit;
timestamping a second reference event with a second reference time determined with respect to the first clock;
providing the first reference event comprising the first reference time to a second interconnected unit;
providing the second reference event comprising the second reference time to the second interconnected unit;
the second interconnected unit timestamping the first reference event with a third reference time in response to receiving the first reference event;
the second interconnected unit timestamping the second reference event with a fourth reference time in response to receiving the second reference event;
wherein the third reference time and the fourth reference time are determined with respect to a second clock used by the second interconnected unit and having a different accuracy than the first clock;
determining during run time at least a first difference between the first reference time and the third reference time and a second difference between the second reference time and the fourth reference time; and
using at least the first and second differences to translate during run time a time measured by at least one of the first clock or the second clock to a time in a different time base from the time to be translated during run time.
12. The method of
13. The method of
14. The method of
15. The method of
16. The method of
17. The method of
18. The method of
19. The method of
20. A system comprising:
a first unit configured to detect a reference event in a first of a plurality of interconnected units;
a first clock configured to determine a first reference time of the detected reference event measured in a first time base;
a first message unit configured to send a first message including the first reference time to a second of the plurality of interconnected units, wherein the second of the plurality of interconnected units uses a second time base based at least in part on a second clock, wherein the first clock and the second clock have different accuracies;
a translation device configured to:
correlate time measurements between the first time base and the second time base during run time using at least one form of translating from a set comprising at least two forms of translating; and
select the form of translating based on, at least in part, a determination of at least one of a linearity of the first and second time bases or a similarity of size of ticks of the first and second time bases, wherein the determination utilizes at least two sets of past reference times, individual sets of past reference times comprising one time in the first time base and a correlated time in the second time base.
21. The system of
22. The system of
23. The system of
24. The system of
25. The system of
26. The system of
27. The system of
28. The system of
29. The system of
30. The system of
31. The system of
32. The system of
33. The system of
34. A system comprising:
a first unit configured to detect a reference event in a first of a plurality of interconnected units, wherein the reference event comprises a bit pattern in a CAN protocol message, and wherein the bit pattern follows an arbitration field;
a first clock configured to determine a first reference time of the reference event measured in a first time base;
a first message unit configured to send a first message including the first reference time to a second of the plurality of interconnected units via a communication channel between the first and the second interconnected units, at least a portion of which comprises a shared potion of the communication channel, wherein the second of the plurality of interconnected units uses a second time base based on a second clock;
a second message unit configured to receive the first message and to timestamp the first message with a time of receipt and send a second message containing a second reference time to the first message unit; and
a translation device configured to determine a communication propagation delay in the shared portion of the communication channel between the first and the second units by using at least the first reference time, the second reference time, and the time of receipt of the first message by the second message unit.
35. The system of
36. The system of
37. The system of
determine a first difference between the first reference time and the time of receipt of the first message by the second message unit;
determine a second difference between the second reference time and the time of receipt of the second message by the first message unit;
determine the communication propagation delay in the shared portion of the communication channel between the first and the second units by determining a difference between the first difference and the second difference.
38. The system of
39. The system of
40. A system comprising:
a first unit configured to detect a reference event in a first one of a plurality of interconnected units;
a first clock configured to determine a first reference time of the detected reference event measured in a first time base, wherein the first clock comprises a time tick generator configured to generate time ticks responsive to movement of a part in a machine;
a first message unit configured to send a first message including the first reference time to a second one of the plurality of interconnected units, wherein the second one of the plurality of interconnected units uses a second time base; and
a translation device configured to:
correlate time measurements between the first time base and the second time base during run time using at least one form of translating from a set consisting of at least two forms of translating; and
select the form of translating based on, at least in part, a determination of at least one of a linearity of the first and second time bases or a similarity of size of time ticks of the first and second time bases, wherein the determination utilizes at least two sets of past reference times, individual sets of past reference times comprising one time in the first time base and a correlated time in the second time base.
41. The system of
42. The system of
43. A method comprising:
timestamping a reference event with a reference time determined with respect to a first clock used by a first interconnected unit, wherein the reference event comprises a bit pattern in a CAN protocol message, and wherein the bit pattern follows an arbitration field;
providing the reference time to a second interconnected unit;
determining a method of correlation between the reference time in the first time base and a reference time in the second time base, the method of correlation being selected from a set of at least two methods of correlation and being selected dependent on at least one of a linearity of the two time bases or a similarity of size of time ticks of each time base; and
using the method of correlation to translate a time measured by the first clock to a time in a different time base during run time.
44. The method of
receiving a message at the first interconnected unit from the second interconnected unit; and
accounting for delays within the first and second interconnected units and for a propagation delay between the first and second interconnected units based on the received message.
45. The method of
46. A method comprising:
maintaining at a computing device a database comprising at least a first set of correlated reference times and a second set of correlated reference times, wherein:
the first set of correlated reference times comprises at least a first reference time for a first reference event timestamped with respect to a first clock used by a first interconnected unit and another first reference time for the first reference event timestamped with respect to a second clock used by a second interconnected unit; and
the second set of correlated reference times comprises at least a second reference time for a second reference event timestamped with respect to the first clock and another second reference time for the second reference event timestamped with respect to the second clock;
translating using a translation function a third reference time for a third reference event timestamped with respect to the first clock to a calculated third reference time for the third reference event comprising a calculated timestamp with respect to the second clock, wherein the translation function utilizes at least the first and second sets of correlated reference times;
determining a difference between the calculated third reference time and an actual third reference time for the third reference event timestamped with respect to the second clock, wherein the difference represents a measurement of at least one of an inaccuracy of the translation function or a nonlinearity of at least one of the first or second clocks.
This application is a continuation under 35 U.S.C. §120 of International Application PCT/SE2005/000581 filed on Apr. 21, 2005. International Application PCT/SE2005/000581 claims priority to Swedish Application 0401130-0 filed on Apr. 30, 2004. The entire contents of each of these applications are incorporated herein by reference.
The present disclosure relates to a fixed and/or moveable 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 moveable 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.
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, analysing, 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:
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:
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:
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:
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:
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 can not 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.
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:
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
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
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
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.
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.
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
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.
An additional variant of the determining of delays is also the one shown in
Both these simple variants of delay determination assume that the Trefs utilize time tick of the same size and that any frequency deviation between the units 501 and 502 can be made negligible or can be compensated for by any of the methods.
A Start-Of-Frame packet, SOF, contains typically a Start-Of-Packet/Sync field 691, an identification field 692, the identification field inverted 693, frame number 694, CRC field 695 and finally an End-Of-Packet field 696.
The unit 603 contains a USB controller 631 which in turn contains a device 632 designed to detect SOF packets 651. The detections in 632 are arranged to trigger a reading of clock 634 to a capture register 633. The time stored in this way is hereafter called Tref. Both the clock 634 and the capture register 633 can be read by the microprocessor 635. Both 633 and 634 should advantageously be able to be incorporated in 635. Program code is stored in the memory 636 which, for example, is run each time 635 receives an SOF packet from 631. The program can, for example, read off the frame number on the SOF packet and, depending upon the requirements and conditions always or at certain intervals read out Tref from 633 and send a new USB packet 652 using 631 via 602 to 601. 603 also contains interface electronics 637 for a CAN controller 638 which, in turn, contains a precise detection mechanism 638′ for detecting when the CAN messages commence.
The detection mechanism 638′ also triggers the capture register 639 which then reads clock 634. The timestamp which is to be found in capture register 639 can be sent, together with the message that triggered the reading in a packet 653 to 601. The packet type 653′ can, for example, include USB overhead, 642 and 642″″, data, 642′, from the CAN controller 638, a timestamp, 642″, of when the data 642′ was received by 638, and if required more data with associated timestamps, 642′″. The packet type 652′ contains, in addition to the overhead, 641, 641″″, that USB adds, a Tref, 641′, the sequence number of the SOF that gave rise to the Tref, 641″, and, if required, more Trefs with associated sequence numbers and/or other data, 641′″.
Computer or processor 601 is arranged with a USB host 671. As already mentioned, 671 sends SOF packets 651 at regular intervals in accordance with the USB protocol. When the computer receives packets of the type 652 from its connected units 603, 603′, etc, via the USB host 671, these can be read and processed by the processor 672 using program code in the memory 673. Among other things, program code according to the logical data flow chart in 680 is run in the processor. Unit 681 represents here the USB drive routines that constitute a part of the operating system that processor 601 utilizes. These contain, among other things, checks on the physical structure of the USB system, and read out the data packets from the controller 671. If these packets originate from any of the units 603, 603′, etc, they are forwarded via the time-handling functions 682 to the drive routines 683 intended for the purpose. If the messages are packets of the type 652, the information 652′ is retrieved from them, that is the so-called Trefs 641′, also the sequence numbers 641″ and any other data 641′″, and they are taken charge of by the time-handling functions 682 which are a part of 683.
The system is, after all, also intended to be used and it is represented here by a user application 685 which logically communicates directly with the units 603, etc, but in practice this is carried out via the commonly used interface 684 which provides all the functions that a user can utilize in the units. The interface 684 thus connects together the program 685 with units' drive routines 683. The interface displays, for example, if so required, all timestamps from the different units along one and the same time axis, which is carried out using the time-handling functions 682 completely in the spirit of the disclosure. In the figure, this is exemplified by the message 653 sent from a unit 603 to 601. Unit 671 decodes the packet and forwards the content 653′ to the processor 672 for further processing. For example, unit 681 sees that the message originates from a unit of type 603 and forwards it to the drive routines 683 intended for the purpose. The time-handling functions 682 in 683 see that the message contains a timestamp 642″ in a local unit's time, and so it translates this to a suitable time according to, for example, the following procedure. The translated time, 643′, and any calculated inaccuracy 643″, are displayed together with data, 643, (that is 642′ possibly further processed by 683) and any other information 643′″, taken as a whole 653″, to the application 685 via the interface 684.
The time-handling functions 682 can be divided into a part that saves and handles a history 682′ of Trefs with sequence numbers that come from the packets 652′ and information about the originating unit and keep translation functions updated and a second part that carries out the actual translations. In order to be able to carry out direct translation between the times of all units, a type of logical translation matrix 686 can be utilized. For each pair of units 687, 687′, etc, whose time is to be able to be translated directly, there is a list 688 with most recently matched pairs of Trefs 688′, 688″, etc. These Trefs 688′, etc, can then be utilized to carry out a translation between the times of the comprised units, for example according to:
where Ax is to be translated to Bx using the matched Tref pairs (Anew, Bnew) and (Aold, Bold) which can thus correspond to 688′ and 688′″. As can be seen, there is a part of the calculations that can be carried out in advance, for example (Bnew−Bold) and (Anew−Aold) in first alternative and (Bnew−Anew) and (Bold−Aold), etc, in second alternative. Such calculations can, as stated, advantageously be performed in advance and saved in a location 689 designed for the purpose in order to simplify and thereby speed up future translations. Statistical inaccuracy concerned can also be calculated and saved in a location 689′ designed for the purpose. It is, of course, possible to make an extremely complex and exhaustive estimate of any inaccuracy on the basis of the whole history of matched Tref pairs, but in order to give a simple illustrative example, one of the Trefs in a pair 688′ can, for example, be translated using two other pairs in the list 688. The translated Tref is then compared with the actual Tref in the pair. The difference between them can be regarded as a simple measurement of inaccuracy/non-linearity.
Another variant of the translation matrix can be to let a row or column represent a virtual time, on the basis, for example, of some weighting of suitable other times.
A simpler variant of the translation matrix is the special case when only one or a few rows or columns in the matrix are kept updated in the way mentioned above. As each row or column can give information about how relating can be carried out from and to a particular time, this time can be utilized as a kind of intermediate master time in translation between two other times. This can be a less memory- and/or resource-intensive alternative to keeping the whole matrix updated at a cost of slightly more complicated translations and/or possibly greater inaccuracy. The intermediate master time here can constitute examples of the function F1.
The time-handling or translation function F2/682 can be broken down into a number of elements that, however, do not all necessarily need to be carried out in each unit arranged with the function. Certain elements can be carried out by one unit that then sends the information to another unit that then does not need to carry out the element. Examples of element functions include:
The time-handling functions can be considered to be an example of the translation function F2.
In the systems, S1 can thus, for example, work with local translation of time, S2 with centralized translation and S3 with local synchronization. Of course, it is also possible to combine different variants in one and the same system.
The event recognitions are to be arranged or are to form the basis for or invoke functionality in the system, such as, for example, analysis. Items of such functionality are represented in
The ECUs controlling rotating parts establish their own time domains on the basis of the speed of rotation. In its simplest form, time base events are generated by pulse-generating wheels 930 and a pulse-detecting device 931. In this example, a pulse is generated with inverted sign by a sensor 932. The device 931 detects the pulse train 933 which is forwarded to the ECU 934 which thereby creates a clock function 934′ with a circular time base with a time tick that corresponds to a rotation of 22.5 degrees. Time is thus measured locally in past wheel angle units. If the wheel stops, then the local time stops. The ECU 934 can control the brakes 935. The time base varies with the speed of rotation of the wheel compared to a time base based on the physical second. A controlling unit 936 with a time base 937 based on the physical second can give commands K1 to and receive reports R1 from the unit 934. By means of status reports from the four wheels, the unit 936 can determine how the wheels are moving relative to each other and command them to increase or decrease the braking force while turning. If a wheel locks, then the time there will stop and reporting will cease. This situation is easily detected by the unit 936, partly by the other wheels reporting, and partly as a result of an expected report in relation to the internal time domain not having arrived.
More complicated time domains can be constructed when expedient. The event generator 940 generates two pulses per revolution with inverted sign and 45 degrees interval. These are detected by the detector unit 941 and transferred to the local translator or counter 942 in the ECU 943 via the link 944. The generated time domain is shown as 945. The ECU 943 has an internal clock 946 which generates the time domain 947. There is a pressure sensor 948 in the system which gives pressure information in discrete steps to the unit 943 via the link 949, where each step can be regarded as an event. Passage of certain of these events can be utilized in order to generate a time tick. The pressure sensor is connected to a cylinder 950 in the motor 901. The ECU 943 controls the electrical valve arrangement 951. The local translator 942 compiles the information from the time domains 945 and 947 and 948 into a new time domain 952 that is suitable for valve control. The control unit 953 gives control commands to the valve control mechanism 951 via the link 954 in the time of the time domain 952. The local translator 942 thereby obtains a clock function viewed from the unit 953. In this way, a “virtual camshaft” can be created, where the characteristics of the control algorithm are changed by the time domain 952 being changed in accordance with variations in speed of revolution and pressure.
A unit 921 can be connected to the system for analysis or diagnostics. The various nodes can have stored in their memories a translation algorithm that states how their respective time domains are transformed to a linear time domain based on the physical second. The instrument 921 can request that the respective modules transmit the translation algorithms. This assumes that the utilized HLP (Higher Layer Protocol) supports such a procedure. Otherwise, the algorithms are to be found in the system's documentation. Alternatively, the algorithms are stored in the system module 920.
The disclosure is not limited to the embodiments described above as examples, but can be modified within the framework of the following claims and the concept of the disclosure.