CN103163870A - Method for scheduling wireless networked control system with maximal tolerant time delay - Google Patents
Method for scheduling wireless networked control system with maximal tolerant time delay Download PDFInfo
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Abstract
The invention discloses a method for scheduling a wireless networked control system with maximal tolerant time delay, and relates to a method for scheduling a network system. The method includes the processes: firstly, sequencing application layers of the industrial networked control system according to priorities specified by the system and extracting a first task in an operation to start building a task scheduling list and setting task start time and stop time; secondly, scheduling a next task in the operation; and thirdly, scheduling all tasks in a next operation, failing in scheduling if calculated theoretical completion time is not shorter than the deadline of the task, and rescheduling and issuing all operations and the tasks in each operation by the application layers of the industrial networked control system. By fully considering the characteristics of wireless communication technology and by the aid of the principle that network time delay is not fully equivalent to instantaneity of the system, the time delay is effectively shortened, instantaneity of the system can be improved, and the disadvantages of wireless communication technology application in the industrial networked control system are made up.
Description
Technical field
The present invention relates to a kind of method of scheduling by natwork system, particularly relate to a kind of method of very big tolerance time delay wireless network networked control systems scheduling.
Background technology
At present, the real-time scheduling method great majority hypothesis channel error rate of using in many wired industrial network control system application layers (system that has tells again client layer) is lower, delays time shorter and stable.Wire transmission is subjected to the impact of industrial environment little, this hypothesis is set up in wired industrial network networked control systems is used, therefore more existing dispatching methods are regarded the functional task in the industrial network networked control systems and communication task as homogeneity, and all tasks all adopt the dispatching method of close-coupled to carry out United Dispatching.This scheduling thought effect in wired industrial network networked control systems is better.Yet the introducing of wireless communication technology makes above hypothesis be false, and wireless channel can be subject to the interference of a large amount of motors and barrier metallization etc. in industrial environment.Consider that wireless channel may be high more a lot of than wire message way error rate in complicated, abominable industrial environment, communication task and functional block task are inhomogeneous.
Even some dispatching methods itself do not adopt combined dispatching mechanism, only adopt the dispatching method of close-coupled to dispatch to communication task, this can make too affects on time completing of subsequent communications task because of previous communication task overtime.This is in present stage and even the very long period in the future, the problem that any wireless communication technology all can't thoroughly solve.For this reason, the dispatching method in former industrial network networked control systems application layer is difficult to reach original real-time effect without suitable improvement in the industry wireless network networked control systems.
In the schedule time list that the close-coupled dispatching method that tradition wired industrial network control system often uses builds a lot of communication tasks be all close-packed arrays together, lower for error rate, shorter and the stable wire message way of delaying time is very suitable, and these characteristics have guaranteed that high-rise operation plan is dispatched on time.And wireless channel is uncertain because of time-delay that the reasons such as error rate height are brought in abominable industrial environment.If it is larger to delay time, can make the scheduling of communication task not to be finished within the scheduling stipulated time, namely this task is overtime.Simultaneously, the close-packed arrays of communication task, the overtime of a communication task may cause follow-up work all overtime, makes the overtime rate of whole system task higher.
Summary of the invention
The object of the present invention is to provide a kind of method of very big tolerance time delay wireless network networked control systems scheduling, the method takes into full account the characteristics of wireless communication technology, utilizing network delay and system real time is not the equivalent relation principle, effectively reduce time delay and can improve system real time, make up wireless communication technology and be applied in inferior position in the industrial network networked control systems.
The objective of the invention is to be achieved through the following technical solutions:
a kind of method of very big tolerance time delay wireless network networked control systems scheduling, described method comprises following flow process: at first with industrial network networked control systems application layer, priority by system's regulation sorts, then put into buffer area by ranking results and wait for scheduling one by one, in the taking-up operation, first task begins to build schedule of tasks, begin start time and the concluding time of the task that arranges, at first judgement task is functional block task or communication task, it is its release time if the functional block task is directly set its start time, current time is to add release time to complete this required by task time, carry out again next task scheduling in operation, until each task in operation is dispatched complete, dispatch again all tasks in next operation, until all complete, if the theoretical deadline that calculates is not less than the off period of this task, think that this dispatching method can't dispatch these tasks on time, dispatch unsuccessfully, industrial network networked control systems application layer should be rearranged the task in All Jobs and each operation of assigning.
The method of described a kind of very big tolerance time delay wireless network networked control systems scheduling, when described task is communication task, at first judge whether the current time has surpassed release time, if surpass, carry out timeout treatment, timeout treatment is general adopts the different disposal method according to concrete control system or customer requirements, can arrange flexibly.
The method of described a kind of very big tolerance time delay wireless network networked control systems scheduling, described release time, if not surpassing release time set its start time is its release time, calculate the theoretical deadline of this communication task, if the theoretical deadline that calculates is less than the off period of this task, directly forcing the deadline is set is the off period, and current time this moment also changes to the deadline immediately.
Advantage of the present invention and effect are:
The present invention tolerates that greatly the communication task in the schedule time list that the dispatching method of radio communication time delay builds is more even in whole grand period profile, there be certain setting aside some time to alleviate the problems such as wireless channel time-delay is long and extremely unstable between each communication task, even communication task has certain delay as long as complete within setting aside some time, can not affect follow-up work begins on time, make in the situation that the physical layer communication delay is higher, can effectively reduce the overtime phenomenon of task in this system.
The present invention has taken into full account the characteristics of wireless communication technology, utilizing network delay and system real time is not the equivalent relation principle, can improve system real time although namely effectively reduce time delay, if but in the constant situation of time delay, improve high-rise Task Scheduling Mechanism and also can reach the effect that improves system real time, proposed a kind of application layer method for scheduling task of very big tolerance radio communication time delay, made up wireless communication technology and be applied in inferior position in the industrial network networked control systems.
Description of drawings
Fig. 1 greatly tolerates the dispatching method process flow diagram of radio communication time delay.
Embodiment
The present invention is described in detail below in conjunction with the accompanying drawing illustrated embodiment.
The inventive method ultimate principle: due in the industry wireless network networked control systems, communication task and functional block task are inhomogeneous, tolerate that greatly the dispatching method of radio communication time delay adopts respectively different scheduling strategies to functional block task scheduling and communication task scheduling.The functional block task scheduling is used the scheduling of close-coupled scheduling strategy, and be to wait until that as far as possible this communication task off period just allows to continue the scheduling follow-up work when arriving to the scheduling strategy of communication task, can be that communication task is reserved the long as far as possible processing time like this.
At first the method according to priority sorts operation, then the sequencing of each task in each operation is being dispatched.At first setting the current time in scheduling process is this task start time, judge that again this task belongs to communication task or functional block task, if the functional block task the theoretical execution time by this task of providing calculates deadline of this task, and judge whether the deadline has exceeded the off period of this task, if exceed carry out corresponding timeout treatment, otherwise will be made as the deadline of this task the current time.Then continue the next task of this operation is dispatched.If next task is communication task, judge at first the current time adds whether the theoretical execution time of its communication task exceeded the off period of this task, this time dispatch unsuccessfully if exceed.If do not exceed the off period of this task, directly be arranged to the off period of this task the deadline of this task.The deadline that will be made as this task the current time continues the next task of this operation is dispatched, and iterative cycles goes down, until each task in All Jobs is scheduled.Its concrete dispatching method process flow diagram is as shown in Figure 1:
This dispatching method has kept the combined dispatching dominance of strategies, with the communication task in whole system and functional block task United Dispatching, and for the uncertain problem of the communication task execution time in wireless channel, be that communication task has been reserved the maximum processing time when processing communication task.
The method mathematical programming model: establishing in network segment of industrial network networked control systems has n task, comprises functional block task and communication task.I task and in the start time in j cycle be for communication task
,
Represent i task and be the start time of functional block task j cycle.M control loop arranged, and the cycle of k control loop is
, and
Be the grand cycle, its value is
Lowest common multiple, k control loop had in the whole grand cycle
The individual microcycle,
Represent i task and be communication task its j microperiodic setting aside some time.
According to the constraint condition of upper surface analysis, can set up the schedule time list that a Nonlinear programming Model is found the solution this dispatching method, model is as follows:
Objective function:
Constraint condition:
(a 1) k control loop
(2) any two possible overlapping communication task i and the constraint of j,
Wherein
With
Being respectively task i set aside some time with adding in the start time in m cycle
After concluding time,
With
Being respectively task j set aside some time with adding in the start time in n cycle
After concluding time.
This model is a typical Nonlinear programming Model, if given one group of data are brought this model into, solution is arranged, and separates
With
The schedule time list that generates based on the dispatching method of very big tolerance radio communication time delay that has formed this network segment.If without solution, explanation, this task-set can't be dispatched.
The inventive method process flow diagram is: at first each operation (comprising functional block task and communication task) of assigning on industrial network networked control systems application layer (system that has tells again client layer) is sorted by the priority that its system stipulates, then put into Job[i by its ranking results] buffer area wait scheduling one by one.Take out operation Job[i] in first task q(be the highest task of priority) begin to build schedule of tasks.Begin to arrange start time and the concluding time of task q, at first judge that task q is functional block task or communication task, be its release time if the functional block task is directly set its start time, the current time is to add release time to complete this required by task time.Carry out again operation Job[i] in next task scheduling (being q++), until operation Job[i] in each task dispatch complete after, then dispatch all tasks (being i++) in next operation, until all complete.When task q is communication task, judge that at first whether the current time surpassed release time, if surpass, carry out timeout treatment.Timeout treatment is general adopts the different disposal method according to concrete control system or customer requirements, can arrange flexibly.If not surpassing release time set its start time is its release time, calculate the theoretical deadline of this communication task, if the theoretical deadline that calculates is less than the off period of this task, directly forcing the deadline is set is the off period, and current time this moment also changes to the deadline immediately.If the theoretical deadline that calculates is not less than the off period of this task, think that this dispatching method can't dispatch these tasks on time, dispatch unsuccessfully.Industrial network networked control systems application layer should be rearranged the task in All Jobs and each operation of assigning.
Hard real-time task in method is for having strict time requirement to off period of task, and task is completed after the off period invalid and may have harmfulness, and this generic task is called again critical tasks.Soft real time task does not have strict time requirement for the off period to task, and task was completed after the off period still has certain value, and this generic task is called again noncritical task.The task of periodic task for repeating according to fixing interval.The aperiodicity task is not for being repeating according to fixing interval of task.Periodically mission critical is to repeat according to fixing interval, and has the task that the strict off period requires.Periodically non-critical task is repeat but there is no the task that the strict off period requires according to fixing interval.Non-periodic, mission critical was repeat but the task that the strict off period requires is arranged not according to fixing interval.Non-periodic, non-critical task was to repeat, also do not have the task of strict off period requirement not according to fixing interval.Preemption scheduling is if in the low priority task implementation, has high-priority task to arrive, and high-priority task stops low priority task by force and seizes execution, and after high-priority task executed, low priority task continued to carry out.Non-preemptive scheduling is if in the low priority task implementation, has high-priority task to arrive, and does not allow high-priority task to seize its resource used, and after waiting this low priority task to execute release resource used, high-priority task just can be carried out.The desirable execution time of task is in the situation that do not consider that task is hindered in the process of implementation, the complete time of using of tasks carrying.The relative off period of task means from the task due in, allows the time interval to the maximum of finishing the work.The absolute off period of task is to equal the due in of task and the relative off period sum of task the absolute off period.The grand cycle of task is the lowest common multiple in the cycle of all periodic tasks.Be the slack time of task under the requirement of satisfying the off period, allows the maximum duration of waiting in buffer zone or formation.Task is overtime is if the deadline of a certain task surpasses its absolute off period, claims that this task is overtime.The time-out time of task is the time that the deadline of task surpasses its off period.Schedulability is for a certain dispatching method, if given one group of specific tasks collection is used a dispatching method, can make any one task in task-set all satisfy its off period requirement, claims that this dispatching method is schedulable to this task-set.Operation be it corresponding to a control loop, be the set that has all tasks of order constraint in control loop.
Obviously, a typical industrial network networked control systems is comprised of a lot of control loops.Build the schedule time list of an industrial network networked control systems, will dispatch the task that all in each operation in this system have an order constraint exactly, will satisfy simultaneously the off period requirement of each task.
Claims (3)
1. very big method of tolerance time delay wireless network networked control systems scheduling, it is characterized in that, described method comprises following flow process: at first with industrial network networked control systems application layer, priority by system's regulation sorts, then put into buffer area by ranking results and wait for scheduling one by one, in the taking-up operation, first task begins to build schedule of tasks, begin start time and the concluding time of the task that arranges, at first judgement task is functional block task or communication task, it is its release time if the functional block task is directly set its start time, current time is to add release time to complete this required by task time, carry out again next task scheduling in operation, until each task in operation is dispatched complete, dispatch again all tasks in next operation, until all complete, if the theoretical deadline that calculates is not less than the off period of this task, think that this dispatching method can't dispatch these tasks on time, dispatch unsuccessfully, industrial network networked control systems application layer should be rearranged the task in All Jobs and each operation of assigning.
2. the method for a kind of very big tolerance time delay wireless network networked control systems scheduling according to claim 1, it is characterized in that, when described task is communication task, at first judge whether the current time has surpassed release time, if surpass, carry out timeout treatment, timeout treatment is general adopts the different disposal method according to concrete control system or customer requirements, can arrange flexibly.
3. the method for a kind of very big tolerance time delay wireless network networked control systems scheduling according to claim 2, it is characterized in that, described release time, if not surpassing release time set its start time is its release time, calculate the theoretical deadline of this communication task, if it is the off period that the theoretical deadline that calculates less than the off period of this task, is directly forced the deadline is set, current time this moment also changes to the deadline immediately.
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Cited By (6)
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| CN105629873A (en) * | 2014-11-07 | 2016-06-01 | 中国科学院沈阳计算技术研究所有限公司 | Hybrid task scheduling method suitable for numerical control system |
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| CN106453141A (en) * | 2016-10-12 | 2017-02-22 | 中国联合网络通信集团有限公司 | Global queue adjustment method, service flow queue adjustment method and network system |
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Application publication date: 20130619 |