JPH06242970A - Real-time multitask system - Google Patents

Abstract

PURPOSE:To restore the system to a state before a system error occurs if the system is disabled to function owing to the system error. CONSTITUTION:This system has a state transition event detecting means 1 which detects an event creating the state transition of the system, a state transition control means 2 which controls the state transition of the system, a state transition confirmation table 3 which stores the state transition corresponding to the event creating the state transition of the system, a state recording 4 which records the state of the system, an action table 5 which stores start/stop information on a task accompanying the state transition corresponding to the event creating the state transition of the system, a task operation switching means 6 which perform start/stop control over the task, a system error detecting means 7 which detects the system error, and a restoring means 8 which restores the state of the task to the state before the system error detection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a real-time multitasking system in which one CPU executes a plurality of tasks in a time-division manner and processes a plurality of events in real time even if a system error occurs. It is used to easily return to the state before the system error occurs and prevent the system error from occurring.

[0002]

2. Description of the Related Art Conventionally, in a single-task system in which one CPU executes one task, in order to determine whether an error has occurred in a task, the time required for the processing in the task is monitored and the time An error detection means called a watchdog timer, which determines that an error has occurred when the time is longer than the time set by the system administrator, is widely used. On the other hand, in a multi-task system in which one CPU executes a plurality of tasks in a time-sharing manner, one task monopolizes the CPU within the time-divided time, but each task is not necessarily in an executing state. In some cases, it is in a waiting state such as waiting for input (a state in which the CPU is waiting without doing anything). The real-time multi-task system tries to process other tasks when it enters this waiting state.

FIG. 2 is a state transition diagram of the real-time multitasking system. In the figure, the execution state is a state in which a task is actually processed by the CPU (RUN). The executable state is a state (READY) in which the task is executable but another task or the like is in the execution state and is waiting for execution. The waiting state is a state (WAIT) in which the CPU cannot be operated due to waiting for input / output or resource request. Each task operates only in the running state.

FIG. 3 shows, as an example, a state of task switching in a general real-time multitasking system. In this system, the priorities of tasks A, B, and C are determined, the priority of tasks is highest, and the priority of tasks C is lowest. When processing requests are simultaneously issued to tasks A, B, and C at time t1 in the figure, task A is activated according to the priority order. Next, at time t2, the task A has an input / output instruction, enters the waiting state for the input / output result, and the task B is activated. When the task ends at time t3, task C is activated. When the input / output instruction of the task A ends at time t4, the task C is switched to the task A. When task A ends at time t5, it switches to task C,
Task C ends at time t6.

[0005]

As described above, the real-time multitask system is required to respond to a plurality of events in real time, and a plurality of tasks operate intricately intertwined with each other. . In such a real-time multitasking system, a system error may occur that renders the entire system inoperable due to an unexpected external event or a defect in a program. When this system error occurs and the system stops functioning, the only way to recover is to restart the entire system and return to the initial state.

The present invention has been made in view of the above points, and an object of the present invention is to provide a system error in a real-time multitask system when a system error occurs and the system stops functioning. It is to provide a means for returning to a state before the occurrence.

[0007]

In the real-time multitasking system of the present invention, in order to solve the above-mentioned problems, as shown in FIG. 1, a state transition event for detecting an event causing a state transition of the system. Detection means 1
And state transition control means 2 for controlling the state transition of the system
A state transition table 3 for storing state transitions according to events that cause system state transitions; a state recording means 4 for recording system states; and tasks associated with state transitions according to events that cause system state transitions. Action table 5 that stores information on the start / stop of
Task operation switching means 6 for controlling start / stop of tasks
And a system error detecting means 7 for detecting a system error, and a returning means 8 for returning the state of the task to the state before the system error is detected.

[0008]

In the real-time multitasking system of the present invention, when an event causing a state transition of the system is detected by the state transition event detecting means 1, the state transition table 3 is referred to and the state transition corresponding to the event is read out. Then, the state transition control means 2 controls the state transition of the system, and the state of the system is recorded in the state recording means 4. For example, in the task switching example shown in FIG. 3, when the event of the end of the input / output instruction of the task A occurs at time t4, the task C transits from the execution state to the waiting state and the task A transits from the waiting state to the execution state. To do. Correspondence between an event causing such a state transition of the system and a state transition caused by the event is registered in advance in the state transition table 3, and the state transition control means 2 refers to the table 3 to refer to the system. Control the state transition of. The action table 5 stores the start / stop status of each task, and the task operation switching unit 6 refers to the action table 5 when the state transition control unit 2 instructs the state transition. , Controls to activate the task in the waiting state or the ready state and to stop the task in the running state. When the system error detecting means 7 detects a system error, the restoring means 8 refers to the state recording means 4 and the action table 5,
Instead of the task operation switching means 6, the start / stop state of each task is switched to restore the state before the system error occurs.

[0009]

1 is a block diagram showing a schematic configuration of a real-time multitasking system of the present invention. This system includes a state transition event detection means 1, a state transition control means 2, a state transition table 3, a state recording means 4, an action table 5, a task operation switching means 6, a system error detection means 7, It is composed of a returning means 8. The state transition event detection means 1 detects an event that causes a state transition of the system and notifies the state transition control means 2 of the event. The state transition table 3 stores state transitions according to events that cause system state transitions. The state transition control means 2 receives an event that causes a state transition of the system, retrieves the state transition corresponding to the event from the state transition table 3, conveys the state transition to the task operation switching means 6, and the state recording means 4 To record. The action table 5 stores the start / stop of the task associated with the state transition according to the event causing the system state transition. The task operation switching unit 6 receives a state transition command from the state transition control unit 2, retrieves task start / stop information corresponding to the state transition from the action table 5, and switches the task operation. The system error detection means 7 detects a system error and notifies the recovery means 8 of the occurrence of the system error. The recovering means 8 receives the system error occurrence from the system error detecting means 7, receives the status before the system error occurrence from the status recording means 4, retrieves from the action table 5 the task start / stop information corresponding to the status, Switch the task behavior.

First, in a normal state in which no system error has occurred, an event for transitioning the system state is detected by the state transition event detection means 1 and transmitted to the state transition control means 2. The state transition control means 2 compares the event transmitted from the state transition event detection means 1 and the system state with the state transition table 3, changes the system state, and records the state in the state recording means 4, and Notify the task operation switching means 6. The task operation switching unit 6 compares the state received from the state transition control unit 2 with the action table 5, and switches the task operation.

Next, when a system error occurs, the system error detecting means 7 detects the system error,
The recovery means 8 is notified that a system error has occurred.
The recovering means 8 is informed by the system error detecting means 7 that a system error has occurred, reads the state before the system error occurs from the state recording means 4, obtains the state of each task from the action table 5, and obtains the system. Switch to the state of each task in the state before the error occurred.

[0012]

According to the real-time multitasking system of the present invention, an event that causes a state transition is detected, the state transition table is referred to, and the task operation is switched so that the state transition corresponding to the event is generated. Since the state of the system is recorded and the system is restored to the state before the system error occurs when the system error occurs, it is possible to prevent the system from going into a runaway state.

[Brief description of drawings]

FIG. 1 is a block diagram of a real-time multitasking system of the present invention.

FIG. 2 is an explanatory diagram showing task state transitions in the present invention.

FIG. 3 is an explanatory diagram showing task switching in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 state transition event detection means 2 state transition control means 3 state transition table 4 state recording means 5 action table 6 task operation switching means 7 system error detection means 8 recovery means

Claims (1)

[Claims] 1. A state transition event detection means for detecting an event causing a system state transition, a state transition control means for controlling a system state transition, and a state transition corresponding to an event causing a system state transition are stored. A state transition table, a state recording unit that records the state of the system, an action table that stores information on the start / stop of a task associated with the state transition that causes an event that causes the state transition of the system, and the start / stop of the task. A real-time multitasking system comprising: a task operation switching means for controlling; a system error detecting means for detecting a system error; and a returning means for returning the task state to the state before the system error detection.