JP2000293254A - Noise reduction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress electromagnetic wave noise generated from CPU during waiting. SOLUTION: In a noise reduction method, plural tasks 12A-12N to which priority is allocated under the control of management software 11 operated by CPU 10 are arranged and a dummy task 13 installed instead of an idle task 11A started during waiting is started. The dummy task 13 is constituted by describing plural control instructions and the control sequence of CPU 10 is changed by the plural control instructions. The operation period of CPU is varied by the change of the control sequence. The frequency of electromagnetic wave noise radiated from CPU is spread and a peak value is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reduction method for reducing electromagnetic noise generated from a computer system such as a personal computer.

[0002]

2. Description of the Related Art Conventionally, various electronic devices have been required to reduce electromagnetic noise generated from each device to a regulated value or less. Hereinafter, this is referred to as EMI countermeasures. One method of EMI countermeasures is to use a shielded structure for the case or cover that stores the equipment, to prevent electromagnetic noise from leaking out, or to partially shield on the circuit board and take EMI countermeasures. Methods are also being considered. Further, a shield member such as rubber or cloth having conductivity may be attached to the inside of the case to obtain a shield structure.

[0003]

In the case where the above-mentioned case or cover has a shield structure, there is a disadvantage that the cost for the case or cover is increased. Furthermore, the adoption of the shield structure increases the weight, which is not suitable for a portable computer or the like. In addition, when a structure in which a shield is partially provided on a circuit board or a structure in which a shield member is attached to the inner surface of a case is employed, it is troublesome, and there is a disadvantage that the cost is increased in this respect. Further, as a recent trend, with the improvement of the operation speed of the CPU (Central Processing Unit), the frequency of the electromagnetic wave noise also increases, the shielding effect is weakened, and the electromagnetic wave noise is easily leaked.
There are also inconveniences that are becoming difficult to take measures.

As one method of solving such a drawback, the period of a clock for operating the CPU is changed, whereby the frequency of electromagnetic wave noise generated from the CPU itself or its periphery is diffused, and the peak value of the electromagnetic wave noise is reduced. There is a way to make it happen. That is, in general, CP
U has an operation speed defined by a clock having a constant period. This is the CPU due to the electromagnetic noise EM concentrated on a clock of a frequency f _N, as shown in FIG. 2 is radiated. It is stipulated that the level of the electromagnetic noise EM must not exceed the regulation value E.

The frequency of electromagnetic wave noise generated from the CPU is diffused as shown in FIG. 3 by randomly varying the clock cycle for operating the CPU, and the peak value of the noise EM is reduced by the frequency diffusion, thereby reducing EMI. Is achieved. However, using this technique requires C
Although the period of the clock applied to the PU must be varied at random, the means required for this is a large-scale device, which causes a disadvantage that the cost is high. Although the above describes the radiation noise of the clock, the same is true for all signals that operate in a particular repetition period. The present invention does not take measures against radiation noise caused by a clock, but adopts a method in which a program operates at a fluctuating cycle so that radiation noise generated by a specific program operating at a fixed cycle does not become a fixed cycle. It is to be reduced by the above.

SUMMARY OF THE INVENTION An object of the present invention is to provide a noise reduction method in which the frequency of electromagnetic noise radiated from a CPU is spread to take EMI countermeasures, and only a part of software is changed without any modification to hardware. In EM
The present invention proposes a noise elimination method capable of taking measure I.

[0007]

According to the present invention, a plurality of tasks having startup priorities are arranged under control of management software, and each task is started in accordance with the priority in response to an activation request from each task. The central processing unit operates in accordance with the execution instructions described in each task, executes desired operations, and executes management software so that the operation does not shift to the idle task provided in the management software when all tasks have been completed. Provide a dummy task with lower priority than the above tasks under control, activate the dummy task while waiting,
The central processing unit is operated in accordance with a plurality of execution instructions described in the dummy task, and the operation sequence of the central processing unit is changed to spread the frequency of electromagnetic wave noise generated with the operation of the central processing unit, and to reduce the electromagnetic wave noise. Is proposed to reduce the peak value of the noise.

According to the noise reduction method of the present invention, it is only necessary to provide a low-priority dummy task under the control of the management software, and there is an advantage that EMI countermeasures can be realized at low cost.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG.
Management software 11 deployed on the PU 10 and a plurality of tasks 12A, 12 arranged under the control of the management software 11.
It is a figure which displayed B, 12C ... 12N notionally. The management software 11 is called, for example, a scheduler, and assigns a priority to start requests from the plurality of tasks 12A to 12N to give start permission. Here, for example, task 12
A description will be given assuming that the order of decreasing priority is added in the order of A, 12B, 12C... 12N. Therefore, if activation requests are issued from all of the tasks 12A to 12N at the same time, the task 12A is activated first and, for example, goes to the status of the keyboard, and if data is input to the keyboard, the data is transmitted. An operation to be taken into the CPU 10 is executed. When the operation of task 12A is completed, task 12A
B is activated, and operations such as transferring the data taken into the CPU 10 to the monitor and displaying data input from the keyboard on the monitor are sequentially executed. The operation of each of the tasks 12A to 12N that output the activation request ends, and if no other activation request is issued, the management software 11 activates the idle task 11A stored therein and enters a standby state.

When the idle task 11A is activated,
Since the idle task 11A only executes, for example, a standby instruction described in one line, the operation sequence (operation procedure) of the CPU 10 operates in the same sequence.
In this state it generates a large electromagnetic noise EM peak value centered on the frequency f _N shown in FIG. This electromagnetic wave noise EM generally has a higher level than the electromagnetic wave noise generated when each of the tasks 12A to 12N is activated.
The electromagnetic noise EM may exceed the regulation value E in some cases.

In the present invention, the dummy task 13 is activated in this standby state without the idle task 11A being activated. The dummy task 13 describes and configures a plurality of dummy control instructions having different numbers of execution cycles, and changes the operation sequence of the CPU 10 by the plurality of dummy control instructions. The frequency can be spread by a dummy control instruction created so that the number of execution cycles changes.

When the operation sequence of the CPU 10 changes, the operation cycle of the CPU 10 substantially fluctuates.
0 and electromagnetic noise EM radiated from the surrounding circuits
The frequency f _N is diffused as shown in FIG. 3, it is possible to suppress the peak value. The suppression rate of the electromagnetic noise EM can be suppressed as the number of execution cycles of the dummy control instruction described in the dummy task 13 can be changed more minutely.

The dummy task 13 includes other tasks 12A to 12A.
Give a lower priority than the priority given to 12N. Therefore, when an activation request is issued from the other tasks 12A to 12N during standby, the task that has output the activation request is preferentially activated.

[0014]

As described above, according to the present invention, the dummy task 13 is provided under the control of the management software 11, and if the dummy task 13 is activated instead of activating the idle task 11A, the CPU 10 The operation sequence can be changed according to the description of the dummy task 13. As a result, the frequency of the electromagnetic noise EM radiated from the CPU 10 and its surroundings is diffused, and the peak value of the electromagnetic noise EM can be reduced.

Therefore, according to the present invention, EMI countermeasures can be achieved by slightly changing the program.
The advantage that the EMI countermeasure can be solved at low cost can be obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram for explaining a noise reduction method according to the present invention.

FIG. 2 is a graph for explaining electromagnetic noise generated in a state where no EMI measure is taken.

FIG. 3 is a graph for explaining electromagnetic noise generated in a state where EMI measures are taken;

[Explanation of symbols]

 10 CPU 11 management software 11A idle task 12A to 12N task 13 dummy task

Claims (1)

[Claims] A plurality of tasks to which start priorities are given are arranged under control of management software, and each task is started in accordance with the priority every time a start request is issued from each task, and is described in each task. A computer in which the operation sequence of the central processing unit is controlled in accordance with an execution instruction to execute a desired operation, and in a state where all the operations of the tasks are completed, an idle task provided in the management software is accessed and the computer enters a standby state. In the system, under the control of the management software, a dummy task having a lower priority than each of the tasks is provided, the dummy task is started when the idle task is accessed, and a plurality of tasks described in the dummy task are set in a standby state. Operating the central processing unit in accordance with the execution instruction of And reducing the peak value of the electromagnetic wave noise by spreading the frequency of the electromagnetic wave noise generated by the operation of the central processing unit.