Time control device

Details Time control device Time control device

1998-08-27

2001-06-26

Roskoski, Bernard (Department: 2859)

Horology: time measuring systems or devices

Time interval

Electrical or electromechanical

Reexamination Certificate

active

06252826

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a time control device, and more particularly to a time control device which is applied in a computer system having a timer function such as the TOD (Time-Of-Day Timer) or a real time clock and controls internal time for realizing the timer function.
BACKGROUND OF THE INVENTION
FIG. 10
is a block diagram showing configuration of a time control device based on the conventional technology. A time control device
40
shown in
FIG. 10
is connected to an external time source
30
, and provides stepping control by receiving time data indicating a reference time and a second pulse (1 second interval) for adjusting timing of such operations as correction (1 second interval). It should be noted that the external time source
30
is a device that transmits a reference time from time reporting service or the like by way of standard electric wave or through a telephone line.
The time control device
40
comprises, as shown in
FIG. 10
, an oscillator
41
oscillating a reference clock with a fixed frequency, a timer
42
for stepping the internal time, a sampling register
43
for sampling the time counted by the timer
42
according to second pulses received from the external time source
30
, a comparing circuit
44
for obtaining an error (&Dgr;T) and advance or delay in stepping by comparing a sampling value obtained by the sampling register
43
to a reference time (time data) value supplied from the external time source
30
, and a correcting circuit
45
for doubling a speed of the time count of the timer
42
or stopping the time count based on the error (&Dgr;T) and advance or delay in stepping transmitted from the comparing circuit
44
in order to correct the internal time.
Next, description is made for operations. In the time control device
40
shown in
FIG. 10
, second pulses oscillated from the external time source
30
and time data are sent to the sampling register
43
and the comparator
44
, respectively. The second pulses are periodically transmitted to the sampling register
43
at an interval of 1 second. For this reason, time data of the timer
42
is sampled at an interval of 1 second in the sampling register
43
.
In the comparing circuit
44
, time data oscillated from the external time source
30
and time data sampled by the sampling register
43
are fetched, and the two time datas are compared to each other. Time obtained by the timer
42
is subtracted from the reference time provided by the external time source
30
, and if the error (&Dgr;T) as a result of comparison is plus, it is determined that the time in the timer
42
is delayed from the reference time, and if the error is minus, it is determined that the time in the timer
42
is advancing from the reference time.
As described above, the error (&Dgr;T) or information on advance or delay obtained by the comparing circuit
44
is supplied to the correcting circuit
45
. In the correcting circuit
45
, when it is determined that the time in the timer
42
is advancing, stop control is provided so that the timer
42
is delayed by the error (&Dgr;T), and when it is determined that the time in the timer
42
is delayed, double speed control is provided so that the timer
42
is advanced by the error (&Dgr;T). Herein the stop control is defined as a control for stopping counting of the reference clock oscillated by the oscillator
41
, and the double speed control is defined as control for counting the reference clock oscillated by the oscillator
41
at a higher speed.
As described above, the timer
42
is controlled by executing the double speed control or stop control so that the timer
42
steps at the same time as the reference time supplied from the external time source
30
.
As a technology analogous to the time control described above, there is the technology disclosed in, for instance, Japanese Patent Laid-Open Publication No. SHO 58-16319. Disclosed in this patent publication is a technology for sending an external clock from an upper computer to a lower computer to adjust the time of the lower computer.
In the time control device based on the conventional technology as described above, when any trouble occurs in the oscillator that operates the timer, stepping under time control may become inaccurate or may stop, and time can not be provided with high precision. Especially, when the oscillator occurs, stepping control over time can not provided, so that the entire system is affected.
Also, in the system, control over the internal time is provided according to the time supplied from an external time source, so that, when the external time source goes wrong, the failure can not be detected, and time correction is executed following an incorrect time supplied from the external time source. In this case, the entire system operates according to a wrong time, which may affect the operations of the entire system.
Also, when any trouble exceeding the precision of the external time source or the internal oscillator occurs, an error in stepping of the time becomes unnecessarily larger, and a correction rate in the correcting circuit also becomes larger. For this reason, satisfactory precision in correction can not be realized by the correcting circuit, or correction itself become impossible, or an extremely long time is required for correction, which makes it possible to realize real time correction.
As described above, when a trouble occurs in the external time source or the oscillator and the trouble is out of the controllable precision range, the cause can not be clarified and the entire system is affected, so that precision or reliability of the internal time becomes disadvantageously lower.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a time control device which can accurately and quickly shoot troubles in an external time source or in an oscillator for keeping high precision and high reliability of the internal time.
With the present invention, oscillating precision of a first and second oscillators each having the same oscillation frequency is determined according to the timing of a signal supplied from an external time source, and a reference clock oscillated by any one of the first and the second oscillator is used according to a result of determination for providing stepping control over the internal time, so that stepping control can be provided over the internal time by using a correct reference clock, whereby it is possible to keep high precision and high reliability of the internal time.
With the present invention, oscillating precision of each of the first and the second oscillator each having the same oscillation frequency is determined according to the timing of a signal supplied from an external time source, and when it is determined that oscillating precision of both of the oscillators is incorrect, correction of stepping of internal time according to the external time source is stopped, so that incorrect stepping correction can be prevented, whereby it is possible to keep high precision and high reliability of the internal time.
With the present invention, sampling values for a certain period of time are obtained from the reference clocks of the first and the second oscillators each having the same frequency according to pulses from an external time source, and stepping control over the internal time is provided by using the reference clocks of the oscillator having a correct oscillating precision determined through comparison of the sampling values to the expected values for the certain period of times, so that, so long as either one of the reference clocks is correct, stepping control can be provided over the internal time using that reference clock, whereby it is possible to keep high precision and high reliability of the internal time.
With the present invention, when it is determined that oscillating precision of both of the first and the second oscillators is incorrect, an alarm indicating defectiveness of the first and the second oscillators as well as of the external time source is generated, so that

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