FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
“FREQUENCY DIFFERENCE DETECTION DEVICE,
FREQUENCY DIFFERENCE DETECTION METHOD,
AND PROGRAM”
SONY CORPORATION, of 1-7-1, Konan, Minato-ku, Tokyo
108-0075, Japan
The following specification particularly describes the invention and the manner in
which it is to be performed.
1
DESCRIPTION
FREQUENCY DIFFERENCE DETECTION DEVICE, FREQUENCY DIFFERENCE DETECTION METHOD, AND PROGRAM
5 TECHNICAL FIELD
[0001]
The present disclosure relates to frequency difference
detection devices, frequency difference detection methods,
and programs, and more particularly, relates to a frequency
10 difference detection device, a frequency difference detection
method, and a program that are suitably used for synchronizing
time information with a master device connected via a network
with high precision.
15 BACKGROUND ART
[0002]
There have been mechanisms for synchronizing time
information between devices connected to each other via a
network, and one of the known examples of such mechanisms is
20 IEEE1588 PTP (precision time protocol) (see Patent Document
1, for example).
[0003]
According to IEEE1588 PTP, PTP messages are exchanged
between a master device (hereinafter referred to as the PTP
25 master) and a slave device (hereinafter referred to as the
PTP slave) connected to each other via a network, so that time
information T2 about the PTP salve can be synchronized with
time information T1 about the PTP master with high precision
on the order of submicroseconds. Specifically, an
30 oscillation frequency f2 in the PTP slave is synchronized with
an oscillation frequency f1 in the PTP master, and the time
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information T2 is then synchronized with the time information
T1.
[0004]
Fig. 1 shows an outline of a conventional high-precision
time synchronization process using 5 IEEE1588 PTP.
[0005]
The PTP master is designed to transmit a Sync message
as a PTP message containing a transmission time T1i over a
network at predetermined intervals Δm based on an oscillation
10 frequency f1. Meanwhile, the PTP slave is designed to receive
the Sync message transmitted from the PTP master, extract the
transmission time T1i contained therein, and acquire the
reception time T2i thereof. That is, the PTP slave obtains
a transmission time T1i and a reception time T2i every time
15 receiving a Sync packet.
[0006]
The PTP slave is also designed to transmit a Delay_req
as a PTP message to the PTP master via a network, and obtain
the transmission time T2X thereof. Having received the
20 Delay_req, the PTP master returns a Delay_res as a PTP message
containing the reception time T1X to the PTP slave. That is,
the PTP slave obtains the transmission time T2X and the
reception time T1X of the Delay_req by transmitting the
Delay_req and receiving the Delay_res as a response thereto.
25 [0007]
However, it is assumed that the time required to
communicate a PTP message such as a Sync message, a Delay_req,
or a Delay_res via a network (hereinafter referred to as the
network delay time) does not vary but is constant.
30 [0008]
In this case, if the oscillation frequency f1 of the
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PTP master is equal to the oscillation frequency f2 of the
PTP slave, the Sync message transmission intervals Δm = T12
- T11 in the PTP master are the same as the Sync message reception
intervals Δs = T22 - T21 in the PTP slave. In other words,
in a case where the difference Δm - Δs between 5 Δm and Δs is
not 0, there is a difference between the oscillation frequency
f1 of the PTP master and the oscillation frequency f2 of the
PTP slave, and synchronization is not established.
[0009]
10 Therefore, to establish frequency synchronization, the
oscillation frequency f2 of the PTP slave should be adjusted
so that the difference Δm - Δs between Δm and Δs (hereinafter
referred to as the frequency difference) will become 0. The
frequency difference Δm - Δs can be expressed by the following
15 equation.
[0010]
Frequency difference Δm - Δs = (T12 - T11) - (T22 - T21)
= (T21 - T11) - (T22 - T12)
[0011]
20 To establish time synchronization, the PTP slave
transmits a Delay_req after frequency synchronization is
established as described above, and receives a Delay_res as
a response, to obtain the transmission time T23 and the
reception time T13 of the Delay_req.
25 [0012]
Specifically, from the following two equations each
expressing a network delay
Network delay = (T22 - time difference) - T12 and
Network delay = T13 - (T23 - time difference),
30 Time difference = {(T22 - T12) - (T13 - T23)}/2
is calculated. The internal clock T2 in the PTP slave
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should be adjusted so that the time difference will become
0.
CITATION LIST
5 PATENT DOCUMENT
[0013]
Patent Document 1: Japanese Patent Application Laid-Open No.
2010-190635
10 SUMMARY OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
[0014]
When high-capacity packets such as video signals flow
in the network to which the PTP master and the PTP slave are
15 connected, a congestion occurs in the network, and the network
delay time for the above described PTP messages might
temporarily become longer.
[0015]
Specifically, as for Sync messages transmitted at
20 transmission times T11, T12, and T13, the network delay time
is constant, as shown in Fig. 2. However, a Sync message
transmitted at a transmission time T14 is delayed by a duration
D1.
[0016]
25 In such a case, the assumption that the network delay
time for the above described PTP messages is constant is not
satisfied. Therefore, frequency synchronization and time
synchronization cannot be accurately established by the above
described method.
30 [0017]
The present disclosure is made in view of those
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circumstances, and aims to synchronize oscillation frequency
with a master device in a network with high precision.
SOLUTIONS TO PROBLEMS
5 [0018]
A frequency difference detection device as one aspect
of the present disclosure is a frequency difference detection
device that detects a difference in oscillation frequency
between a master device and a slave device connected to each
10 other via a network. The frequency difference detection
device includes: a first subtracting unit that calculates a
difference between a transmission time T1 contained in a sync
message transmitted periodically from the master device and
a reception time T2 at which the message has been received;
15 a second subtracting unit that calculates a difference between
a result of a subtraction T2i - T1i performed by the first
subtracting unit for the sync message received for the ith
time, and a result of a subtraction T2i-k - T1i-k performed by
the first subtracting unit for the sync message received for
20 the (i - k)th time; and a first dividing unit that divides
a result of the subtraction performed by the second subtracting
unit by k.
[0019]
The frequency difference detection device as the one
25 aspect of the present disclosure may further include: a third
subtracting unit that calculates a difference between the
result of the subtraction T2i - T1i performed by the first
subtracting unit for the sync message received for the ith
time and a result of a subtraction T2i-k+j - T1i-k+j performed
30 by the first subtracting unit for the sync message received
for the (i - k + j)th time (j being an integer smaller than
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k); a second dividing unit that divides a result of the
subtraction performed by the third subtracting unit by k -
j; a switch that outputs a result of the division performed
by the first dividing unit with k or a result of the division
performed by the second dividing unit with k 5 - j; and a switch
control unit that controls the switch.
[0020]
In the slave device, the oscillation frequency may be
adjusted to obtain 0 as the result of the division performed
10 by the first dividing unit with k or the result of the division
performed by the second dividing unit with k - j, either of
the results being output from the switch.
[0021]
Under the control of the switch control unit, the switch
15 may output the result of the division performed by the first
dividing unit with k, the result of the division performed
by the second dividing unit with k - j, or the value 0.
[0022]
When the absolute value of the result of the subtraction
20 performed by the second subtracting unit is equal to or smaller
than a predetermined threshold value, the switch control unit
may cause the switch to output the result of the division
performed by the first dividing unit with k. When the absolute
value of the result of the subtraction performed by the second
25 subtracting unit is greater than the predetermined threshold
value, and the absolute value of the result of the subtraction
performed by the third subtracting unit is equal to or smaller
than the predetermined threshold value, the switch control
unit may cause the switch to output the result of the division
30 performed by the second dividing unit with k - j. When the
absolute value of the result of the subtraction performed by
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the second subtracting unit is greater than the predetermined
threshold value, and the absolute value of the result of the
subtraction performed by the third subtracting unit is greater
than the predetermined threshold value, the switch control
unit may cause the switch to output 5 the value 0.
[0023]
The frequency difference detection device as the one
aspect of the present disclosure may further include: a fourth
subtracting unit that calculates a difference between the
10 result of the subtraction T2i - T1i performed by the first
subtracting unit for the sync message received for the ith
time and a result of a subtraction T2i-1 - T1i-1 performed by
the first subtracting unit for the sync message received for
the (i - 1)th time; and a determining unit that detects an
15 increase, a decrease, or no variations in network delay time
based on a result of the subtraction performed by the fourth
subtracting unit.
[0024]
When the number of times an increase in the network delay
20 time has been detected is equal to the number of times a decrease
in the network delay time has been detected among results of
the last k detections performed by the determining unit, the
switch control unit may cause the switch to output the result
of the division performed by the first dividing unit with k.
25 When the number of times an increase in the network delay time
has been detected differs from the number of times a decrease
in the network delay time has been detected among the results
of the last k detections performed by the determining unit,
and the number of times an increase in the network delay time
30 has been detected is equal to the number of times a decrease
in the network delay time has been detected among results of
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the last (k - 1) detections performed by the determining unit,
the switch control unit may cause the switch to output the
result of the division performed by the second dividing unit
with k - j. When the number of times an increase in the network
delay time has been detected differs from the 5 number of times
a decrease in the network delay time has been detected among
the results of the last k detections performed by the
determining unit, and the number of times an increase in the
network delay time has been detected differs from the number
10 of times a decrease in the network delay time has been detected
among the results of the last (k - 1) detections performed
by the determining unit, the switch control unit may cause
the switch to output the value 0.
[0025]
15 A frequency difference detection method as one aspect
of the present disclosure is a frequency difference detection
method implemented in a frequency difference detection device
that detects a difference in oscillation frequency between
a master device and a slave device connected to each other
20 via a network. The frequency difference detection method
includes: a first subtracting step of calculating a difference
between a transmission time T1 contained in a sync message
transmitted periodically from the master device and a reception
time T2 at which the message has been received; a second
25 subtracting step of calculating a difference between a result
of a subtraction T2i - T1i performed in the first subtracting
step for the sync message received for the ith time, and a
result of a subtraction T2i-k - T1i-k performed in the first
subtracting step for the sync message received for the (i -
30 k)th time; and a dividing step of dividing a result of the
subtraction performed in the second subtracting step by k,
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the steps being carried out by the frequency difference
detection device.
[0026]
A program as one aspect of the present disclosure is
a program to be executed by a computer that detects 5 a difference
in oscillation frequency between a master device and a slave
device connected to each other via a network. The program
causes the computer to function as: a first subtracting unit
that calculates a difference between a transmission time T1
10 contained in a sync message transmitted periodically from the
master device and a reception time T2 at which the message
has been received; a second subtracting unit that calculates
a difference between a result of a subtraction T2i - T1i performed
by the first subtracting unit for the sync message received
15 for the ith time, and a result of a subtraction T2i-k - T1i-k
performed by the first subtracting unit for the sync message
received for the (i - k)th time; and a dividing unit that divides
a result of the subtraction performed by the second subtracting
unit by k.
20 [0027]
In one aspect of the present disclosure, a difference
between a transmission time T1 contained in a sync message
transmitted periodically from a master device and a reception
time T2 at which the message has been received is calculated,
25 and a difference between a result of the subtraction T2i -
T1i for the sync message received for the ith time and a result
of the subtraction T2i-k - T1i-k for the sync message received
for the (i - k)th time is divided by k.
30 EFFECTS OF THE INVENTION
[0028]
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According to one aspect of the present disclosure,
oscillation frequency can be synchronized with a master device
in a network with high precision.
BRIEF DESCRIPTION 5 OF DRAWINGS
[0029]
Fig. 1 is a diagram showing an outline of a conventional
high-precision time synchronization process using IEEE1588
PTP.
10 Fig. 2 is a diagram showing an example case where the
network delay time temporarily varies.
Fig. 3 is a block diagram showing a first example
structure of a frequency difference detection device as an
embodiment of the present disclosure.
15 Fig. 4 is a block diagram showing a second example
structure of the frequency difference detection device as an
embodiment of the present disclosure.
Fig. 5 is a block diagram showing a third example
structure of the frequency difference detection device as an
20 embodiment of the present disclosure.
Fig. 6 is a diagram showing the relationship between
the transmission time T1i-k and the reception time T2i-k of the
Sync message received k Sync messages earlier.
Fig. 7 is a flowchart for explaining an operation of
25 the third example structure of the frequency difference
detection device.
Fig. 8 is a diagram showing outputs of the third example
structure of the frequency difference detection device.
Fig. 9 is a block diagram showing a fourth example
30 structure of the frequency difference detection device as an
embodiment of the present disclosure.
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Fig. 10 is a flowchart for explaining an operation of
the third example structure of the frequency difference
detection device.
Fig. 11 is a block diagram showing a third example
structure of the frequency difference detection 5 device as an
embodiment of the present disclosure.
Fig. 12 is a diagram for explaining an operation of the
fourth example structure of the frequency difference detection
device.
10 Fig. 13 is a flowchart for explaining an operation of
the fourth example structure of the frequency difference
detection device.
Fig. 14 is a block diagram showing an example structure
of a computer.
15
MODE FOR CARRYING OUT THE INVENTION
[0030]
The following is a detailed description of the best modes
for carrying out the present disclosure (hereinafter referred
20 to as embodiments), with reference to the drawings.
[0031]
A frequency difference detection device that is an
embodiment of the present disclosure is included in a PTP slave
(a slave device) that exchanges PTP messages with a PTP master
25 (a master device) in a network so as to have time information
synchronized with the PTP master.
[0032]
This frequency difference detection device detects Δm
- Δs as information for synchronizing the oscillation frequency
30 f2 of the PTP slave with the oscillation frequency f1 of the
PTP master without error. In the PTP slave including this
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frequency difference detection device, frequency
synchronization is established by adjusting the oscillation
frequency f2 so that the detected Δm - Δs will become 0.
[0033]
[First Example Structure of the Frequency 5 Difference
Detection Device]
Fig. 3 shows a first example structure of the frequency
difference detection device as an embodiment. This frequency
difference detection device 10 includes a subtracting unit
10 11, a 1-sequence delaying unit 12, a subtracting unit 13, and
a median filter 18.
[0034]
Every time the PTP slave including the frequency
difference detection device 10 receives a Sync message as a
15 PTP message, the subtracting unit 11 subtracts the transmission
time T1i from the reception time T2i, and outputs the subtraction
result T2i - T1i to the 1-sequence delaying unit 12 and the
subtracting unit 13.
[0035]
20 The 1-sequence delaying unit 12 stores the subtraction
result T2i - T1i, which is input from the subtracting unit
11, and outputs the subtraction result T2i-1 - T1i-1
corresponding to the Sync message that has been received last
time and been stored to the subtracting unit 13.
25 [0036]
The subtracting unit 13 subtracts the subtraction result
T2i-1 - T1i-1 corresponding to the Sync message received last
time from the subtraction result T2i - T1i corresponding to
the Sync message received this time, and outputs the
30 subtraction result (T2i - T1i) - (T2i-1 - T1i-1) as a frequency
difference Δm - Δs, to the median filter 18.
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[0037]
The median filter 18 is formed with 1-sequence delaying
units 14-1 through 14-3, a selecting unit 15, an adding unit
16, and a dividing unit 17. The 1-sequence delaying units
14-1 through 14-3 store frequency differences 5 Δm - Δs, which
are input from the previous stage, and outputs the frequency
differences Δm - Δs that have been input for the first time
and been stored to the later stage. The selecting unit 15
compares four frequency differences Δm - Δs, which are
10 simultaneously input from the subtracting unit 13 and the
1-sequence delaying units 14-1 through 14-3, selects the two
out of the four values excluding the largest and smallest values,
and outputs the selected values to the adding unit 16. The
adding unit 16 adds up the selected two frequency differences
15 Δm - Δs, and outputs the result to the dividing unit 17. The
dividing unit 17 divides the result of the addition of the
two frequency differences Δm - Δs by 2.
[0038]
[Description of Operation]
20 An operation of the frequency difference detection
device 10 is now described.
[0039]
When the PTP slave including the frequency difference
detection device 10 receives a Sync message as a PTP message,
25 the subtracting unit 11 subtracts the transmission time T1i
from the reception time T2i, and outputs the subtraction result
T2i - T1i to the 1-sequence delaying unit 12 and the subtracting
unit 13.
[0040]
30 The 1-sequence delaying unit 12 stores the subtraction
result T2i - T1i, which has been input from the subtracting
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unit 11, and outputs the subtraction result T2i-1 - T1i-1
corresponding to the Sync message that has been received last
time and been stored, to the subtracting unit 13.
[0041]
The subtracting unit 13 subtracts the 5 subtraction result
T2i-1 - T1i-1 corresponding to the Sync message received last
time from the subtraction result T2i - T1i corresponding to
the Sync message received this time, and outputs the
subtraction result (T2i - T1i) - (T2i-1 - T1i-1) as a frequency
10 difference Δm - Δs, to the median filter 18.
[0042]
The median filter 18 compares a total of four frequency
differences including the frequency difference Δm - Δs, which
has been input from the subtracting unit 13, and the frequency
15 differences Δm - Δs, which have been input one Sync message
earlier, two Sync messages earlier, and three Sync messages
earlier, and outputs the average value between the two values
out of those four values excluding the largest and smallest
values.
20 [0043]
In the PTP slave, the oscillation frequency f2 is adjusted
so that the averaged frequency difference Δm - Δs will be 0.
[0044]
As described above, the frequency difference detection
25 device 10 outputs the average value between the two values
out of the four successive frequency differences Δm - Δs
excluding the largest and smallest values as the ultimate
frequency difference Δm - Δs. Accordingly, it is possible
to cope with variations in network delay time that occur in
30 a pulse-like manner.
[0045]
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When variations in network delay time successively occur
in the frequency difference detection device 10, however, the
ultimate frequency difference Δm - Δs is also affected by the
variations in network delay time, and as a result,
high-precision frequency synchronization 5 cannot be
established.
[0046]
In view of this, an example structure of a frequency
difference detection device designed not to output a frequency
10 difference Δm - Δs affected by variations in network delay
time is described next.
[0047]
[Second Example Structure of the Frequency Difference
Detection Device]
15 Fig. 4 shows a second example structure of the frequency
difference detection device as an embodiment. This frequency
difference detection device 20 includes a subtracting unit
21, a 1-sequence delaying unit 22, a subtracting unit 23, a
comparing unit 24, and a switch 25.
20 [0048]
Every time the PTP slave including the frequency
difference detection device 20 receives a Sync message as a
PTP message, the subtracting unit 21 subtracts the transmission
time T1i from the reception time T2i, and outputs the subtraction
25 result T2i - T1i to the 1-sequence delaying unit 22 and the
subtracting unit 23.
[0049]
The 1-sequence delaying unit 22 stores the subtraction
result T2i - T1i, which is input from the subtracting unit
30 21, and outputs the subtraction result T2i-1 - T1i-1
corresponding to the Sync message that has been received last
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time and been stored, to the subtracting unit 23.
[0050]
The subtracting unit 23 subtracts the subtraction result
T2i-1 - T1i-1 corresponding to the Sync message received last
time from the subtraction result T2i - T1i 5 corresponding to
the Sync message received this time, and outputs the
subtraction result (T2i - T1i) - (T2i-1 - T1i-1) as a frequency
difference Δm - Δs, to the comparing unit 24 and an input terminal
25a of the switch 25.
10 [0051]
The comparing unit 24 compares the absolute value |Δm
- Δs| of the frequency difference that is input from the
subtracting unit 23 with a predetermined threshold value, and
controls the switching of the switch 25 in accordance with
15 the comparison result.
[0052]
The switch 25 performs switching under the control of
the comparing unit 24, and outputs the frequency difference
Δm - Δs, which is input to the input terminal 25a, or the value
20 0, which is input to an input terminal 25b to the later stage.
[0053]
[Description of Operation]
An operation of the frequency difference detection
device 20 is now described.
25 [0054]
When the PTP slave including the frequency difference
detection device 20 receives a Sync message as a PTP message,
the subtracting unit 21 subtracts the transmission time T1i
from the reception time T2i, and outputs the subtraction result
30 T2i - T1i to the 1-sequence delaying unit 22 and the subtracting
unit 23.
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[0055]
The 1-sequence delaying unit 22 stores the subtraction
result T2i - T1i, which has been input from the subtracting
unit 21, and outputs the subtraction result T2i-1 - T1i-1
corresponding to the Sync message that has 5 been received last
time and been stored, to the subtracting unit 23.
[0056]
The subtracting unit 23 subtracts the subtraction result
T2i-1 - T1i-1 corresponding to the Sync message received last
10 time from the subtraction result T2i - T1i corresponding to
the Sync message received this time, and outputs the
subtraction result (T2i - T1i) - (T2i-1 - T1i-1) as a frequency
difference Δm - Δs, to the comparing unit 24 and the input
terminal 25a of the switch 25.
15 [0057]
The comparing unit 24 determines whether the absolute
value |Δm - Δs| of the frequency difference that is input from
the subtracting unit 23 is larger than the predetermined
threshold value. If the determination result is positive,
20 the switch 25 switches to the input terminal b. As a result,
the switch 25 outputs the value 0 to the later stage. If the
determination result is negative, on the other hand, the switch
25 switches to the input terminal a. As a result, the switch
25 outputs the frequency difference Δm - Δs that has been input
25 from the subtracting unit 23 to the later stage.
[0058]
As described above, in the frequency difference
detection device 20, when the absolute value |Δm - Δs| of the
frequency difference that has been input from the subtracting
30 unit 23 is larger than the predetermined threshold value, or
when the frequency difference Δm - Δs is greatly affected by
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variations in network delay time, the value 0 is output, instead
of the frequency difference Δm - Δs. Accordingly, the
oscillation frequency f2 of the PTP slave can be prevented
from being adjusted while there are variations in network delay
5 time.
[0059]
While the value 0 is output instead of the frequency
difference Δm - Δs, the oscillation frequency f2 is not adjusted.
Therefore, if this situation occurs in an initial stage of
10 frequency synchronization, the time required for
synchronizing the oscillation frequency f2 with the
oscillation frequency f1 of the PTP master might become long.
[0060]
In view of this, an example structure of a frequency
15 difference detection device capable of keeping the frequency
difference Δm - Δs from the influence of variations in network
delay time is described next.
[0061]
[Third Example Structure of the Frequency Difference
20 Detection Device]
Fig. 5 shows a third example structure of the frequency
difference detection device as an embodiment. This frequency
difference detection device 30 includes a subtracting unit
31, a k-sequence delaying unit 32, a subtracting unit 33, and
25 a dividing unit 34.
[0062]
Every time the PTP slave including the frequency
difference detection device 30 receives a Sync message as a
PTP message, the subtracting unit 31 subtracts the transmission
30 time T1i from the reception time T2i, and outputs the difference
T2i - T1i to the k-sequence delaying unit 32 and the subtracting
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unit 33.
[0063]
The k-sequence delaying unit 32 stores the difference
T2i - T1i, which is input from the subtracting unit 31, and
outputs the difference T2i-k - T1i-k corresponding 5 to the Sync
message that has been received k Sync messages earlier and
been stored, to the subtracting unit 33. Here, k is an integer
of 2 or greater, and is preferably a multiple of 2, with the
circuit design of the k-sequence delaying unit 32 being taken
10 into consideration. For example, k is 8, 16, or the like.
[0064]
Fig. 6 shows the relationships between the transmission
time T1i and the reception time T2i of the Sync message received
this time, and the transmission time T1i-k and the reception
15 time T2i-k of the Sync message received k Sync messages earlier,
in a case where k = 8. When attention is paid to the
communication period for k Sync messages indicated by A in
the drawing, variations in network delay time have occurred
within the communication period. However, as attention is
20 paid only to the relationships between the transmission time
T1i and the reception time T2i of the current Sync message,
and the transmission time T1i-k and the reception time T2i-k
of the Sync message that has been received k Sync messages
earlier than the current Sync message, there is no influence
25 of variations in network delay time that have occurred within
the communication period.
[0065]
The subtracting unit 33 subtracts the difference T2i-k
- T1i-k corresponding to the Sync message received k Sync
30 messages earlier from the difference T2i - T1i corresponding
to the Sync message received this time, and outputs the
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difference (T2i - T1i) - (T2i-k - T1i-k) = Δm × k - Δs × k to
the dividing unit 34.
[0066]
The dividing unit 34 divides the difference Δm × k -
Δs × k, which is input from the subtracting 5 unit 33, by k,
and outputs the frequency difference Δm - Δs obtained as a
result to the later stage.
[0067]
[Description of Operation]
10 An operation of the frequency difference detection
device 30 is now described.
[0068]
Fig. 7 is a flowchart for explaining a frequency
difference detection process to be performed by the frequency
15 difference detection device 30.
[0069]
When the PTP slave including the frequency difference
detection device 30 receives a Sync message as a PTP message,
the subtracting unit 31 in step S1 subtracts the transmission
20 time T1i from the reception time T2i, and outputs the difference
T2i - T1i as the subtraction result to the k-sequence delaying
unit 32 and the subtracting unit 33.
[0070]
In step S2, the k-sequence delaying unit 32 stores the
25 difference T2i - T1i, which has been input from the subtracting
unit 31, and outputs the difference T2i-k - T1i-k corresponding
to the Sync message that has been received k Sync messages
earlier and been stored, to the subtracting unit 33.
[0071]
30 The subtracting unit 33 subtracts the difference T2i-k
- T1i-k corresponding to the Sync message received k Sync
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messages earlier from the difference T2i - T1i corresponding
to the Sync message received this time, and outputs the
subtraction result (T2i - T1i) - (T2i-k - T1i-k) = Δm × k - Δs
× k to the dividing unit 34.
5 [0072]
In step S3, the dividing unit 34 divides the difference
Δm × k - Δs × k, which has been input from the subtracting
unit 33 by k, and outputs the frequency difference Δm - Δs
obtained as the division result to the later stage.
10 [0073]
In the PTP slave, the oscillation frequency f2 is adjusted
so that the frequency difference Δm - Δs obtained as the division
result will be 0.
[0074]
15 As described above, even when variations in network delay
time have occurred within the communication period for k Sync
messages as shown in Fig. 6A, the frequency difference
detection device 30 can detect a frequency difference Δm -
Δs without the influence of the variations. Accordingly, in
20 the PTP slave including the frequency difference detection
device 30, frequency synchronization can be established with
high precision.
[0075]
However, in a case where a variation in network delay
25 time has occurred at an edge of the communication period for
k Sync messages (at the start (k Sync messages earlier) in
the case of Fig. 6A) as shown in Fig. 6B, the difference to
be output from the subtracting unit 33 is Δm × k - Δs × k -
D1 as shown in Fig. 8. Therefore, the output of the dividing
30 unit 34 is Δm - Δs - D1/k, and adjustment of the oscillation
frequency f2 involves an error equivalent to -D1/k. If the
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value of k is large, however, the value of -D1/k is small,
and the influence thereof may be ignored.
[0076]
In view of this, an example structure of a frequency
difference detection device capable of keeping 5 the frequency
difference Δm - Δs from the influence of a variation in network
delay time that has occurred at an edge of the communication
period for k Sync messages is described next.
[0077]
10 [Fourth Example Structure of the Frequency Difference
Detection Device]
Fig. 9 shows a fourth example structure of the frequency
difference detection device as an embodiment. This frequency
difference detection device 40 includes a subtracting unit
15 41, a (k - 1)-sequence delaying unit 42, a 1-sequence delaying
unit 43, a subtracting unit 44, a comparing unit 45, a dividing
unit 46, a switch 47, a subtracting unit 48, a comparing unit
49, a dividing unit 50, and a switch 51.
[0078]
20 Every time the PTP slave including the frequency
difference detection device 40 receives a Sync message as a
PTP message, the subtracting unit 41 subtracts the transmission
time T1i from the reception time T2i, and outputs the difference
T2i - T1i to the (k - 1)-sequence delaying unit 42, the
25 subtracting unit 44, and the subtracting unit 48.
[0079]
The (k - 1)-sequence delaying unit 42 stores the
difference T2i - T1i, which is input from the subtracting unit
41, and outputs the difference T2i-k+1 - T1i-k+1 corresponding
30 to the Sync message that has been received (k - 1) Sync messages
earlier and been stored, to the 1-sequence delaying unit 43
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and the subtracting unit 44. Here, k is an integer of 2 or
greater. For example, k is 8, 16, or the like.
[0080]
The 1-sequence delaying unit 43 stores the difference
T2i-k+1 - T1i-k+1, which is input from the (k - 1)-5 sequence delaying
unit 42, and outputs the difference T2i-k - T1i-k corresponding
to the Sync message that has been received k Sync messages
earlier and been stored, to the subtracting unit 48.
[0081]
10 The subtracting unit 44 subtracts the difference T2i-k+1
- T1i-k+1 corresponding to the Sync message received (k - 1)
Sync messages earlier from the difference T2i - T1i
corresponding to the Sync message received this time, and
outputs the difference (T2i - T1i) - (T2i-k+1 - T1i-k+1) = Δm ×
15 (k - 1) - Δs × (k - 1) to the comparing unit 45 and the dividing
unit 46.
[0082]
The comparing unit 45 compares the absolute value |(Δm
- Δs) × (k - 1)| of the difference that is input from the
20 subtracting unit 44 with a predetermined threshold value, and
controls the switching of the switch 47 in accordance with
the comparison result.
[0083]
The dividing unit 46 divides the difference (Δm - Δs)
25 × (k - 1), which is input from the subtracting unit 44, by
(k - 1), and outputs the frequency difference Δm - Δs obtained
as a result to an input terminal 47a of the switch 47.
[0084]
The switch 47 performs switching under the control of
30 the comparing unit 45, and outputs the frequency difference
Δm - Δs, which is input from the dividing unit 46 to the input
24
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terminal 47a, or the value 0, which is input to an input terminal
47b to an input terminal 51b of the switch 51.
[0085]
The subtracting unit 48 subtracts the difference T2i-k
- T1i-k corresponding to the Sync message 5 received k Sync
messages earlier from the difference T2i - T1i corresponding
to the Sync message received this time, and outputs the
difference (T2i - T1i) - (T2i-k - T1i-k) = Δm × k - Δs × k to
the comparing unit 49 and the dividing unit 50.
10 [0086]
The comparing unit 49 compares the absolute value |(Δm
- Δs) × k| of the difference that is input from the subtracting
unit 48 with a predetermined threshold value, and controls
the switching of the switch 51 in accordance with the comparison
15 result.
[0087]
The dividing unit 50 divides the difference (Δm - Δs)
× k, which is input from the subtracting unit 48, by k, and
outputs the frequency difference Δm - Δs obtained as a result
20 to an input terminal 51a of the switch 51.
[0088]
The switch 51 performs switching under the control of
the comparing unit 49, and outputs the frequency difference
Δm - Δs, which is input from the dividing unit 50 to the input
25 terminal 51a, or the output of the switch 47 that is input
to the input terminal 51b (the frequency difference Δm - Δs,
which is output from the dividing unit 46, or the value 0)
to the later stage.
[0089]
30 [Description of Operation]
An operation of the frequency difference detection
25
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device 40 is now described. Fig. 10 is a flowchart for
explaining a frequency difference detection process to be
performed by the frequency difference detection device 40.
[0090]
When the PTP slave including the frequency 5 difference
detection device 40 receives a Sync message as a PTP message,
the subtracting unit 41 in step S11 subtracts the transmission
time T1i from the reception time T2i, and outputs the difference
T2i - T1i to the (k - 1)-sequence delaying unit 42, the
10 subtracting unit 44, and the subtracting unit 48.
[0091]
In step S12, the subtracting unit 44 subtracts the
difference T2i-k+1 - T1i-k+1, which has been input from the (k
- 1)-sequence delaying unit 42 and corresponds to the Sync
15 message received (k - 1) Sync messages earlier, from the
difference T2i - T1i corresponding to the Sync message received
this time, and outputs the difference (T2i - T1i) - (T2i-k+1
- T1i-k+1) = Δm × (k - 1) - Δs × (k - 1) to the comparing unit
45 and the dividing unit 46.
20 [0092]
In step S13, the dividing unit 46 divides the difference
(Δm - Δs) × (k - 1), which has been input from the subtracting
unit 44, by (k - 1), and outputs the frequency difference Δm
- Δs obtained as a result to the input terminal 47a of the
25 switch 47. Meanwhile, the comparing unit 45 determines
whether the absolute value |(Δm - Δs) × (k - 1)| of the difference
that is input from the subtracting unit 44 is greater than
a predetermined threshold value. If the determination result
is positive, the process moves on to step S14, and the switch
30 47 switches to the input terminal 47b under the control of
the comparing unit 45, and outputs the value 0 to the input
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terminal 51b of the switch 51. If the determination result
in step S13 is negative, on the other hand, the process moves
on to step S15, and the switch 47 switches to the input terminal
47a under the control of the comparing unit 45, and outputs
the frequency difference Δm - Δs, which 5 is input from the
dividing unit 46, to the input terminal 51b of the switch 51.
[0093]
In step S16, the subtracting unit 48 subtracts the
difference T2i-k - T1i-k, which has been input from the 1-sequence
10 delaying unit 43 and corresponds to the Sync message received
k Sync messages earlier, from the difference T2i - T1i
corresponding to the Sync message received this time, and
outputs the difference (T2i - T1i) - (T2i-k - T1i-k) = Δm × k
- Δs × k to the comparing unit 49 and the dividing unit 50.
15 [0094]
In step S17, the dividing unit 50 divides the difference
(Δm - Δs) × k, which has been input from the subtracting unit
48, by k, and outputs the frequency difference Δm - Δs obtained
as a result to the input terminal 51a of the switch 51.
20 Meanwhile, the comparing unit 49 determines whether the
absolute value |(Δm - Δs) × k| of the difference that is input
from the subtracting unit 48 is greater than a predetermined
threshold value. If the determination result is positive,
the process moves on to step S18, and the switch 51 switches
25 to the input terminal 51b under the control of the comparing
unit 49, and outputs the output of the switch 47 to the later
stage. If the determination result in step S17 is negative,
on the other hand, the process moves on to step S19, and the
switch 51 switches to the input terminal 51a under the control
30 of the comparing unit 49, and outputs the frequency difference
Δm - Δs, which is input from the dividing unit 50, to the later
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stage.
[0095]
In the PTP slave, the oscillation frequency f2 is adjusted
so that the frequency difference Δm - Δs obtained as the division
5 result will be 0.
[0096]
As described above, in a case where variations in network
delay time have occurred within the communication period for
k Sync messages as shown in Fig. 6B, for example, the frequency
10 difference detection device 40 detects a frequency difference
based on the (k-1) Sync messages communication period that
is shorter than the above communication period by the time
equivalent to one Sync message and does not have variations
in network delay time as shown in Fig. 6C. In the PTP slave
15 including the frequency difference detection device 40,
frequency synchronization can be established with high
precision.
[0097]
The frequency difference detection device 40 outputs
20 one of the frequency differences with respect to the k Sync
messages communication period and the (k - 1) Sync messages
communication period. However, frequency differences with
respect to communication periods further including stepwise
a (k - 2) Sync messages communication period and a (k - 3)
25 Sync messages communication period may be detected, for example,
and a frequency difference not affected by variations in
network delay time may be selected from those frequency
differences and be output.
[0098]
30 Meanwhile, the predetermined threshold value to be
compared with the input from the subtracting unit 48 at the
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comparing unit 49 of the frequency detection device 40 is
determined in the manner described below, for example.
[0099]
The frequency variable range of a VCO (voltage controlled
oscillator) mounted on each of the PTP master 5 and the PTP slave
is ±300 ppm, each Sync message transmission interval is 1/64
second, and the largest possible difference between the
frequency f2 of the PTP slave and the frequency f1 of the PTP
master is 100 ppm. In this case, due to the largest frequency
10 difference 100 ppm, an error of 1.5 μs (= 100 ppm/64) might
occur in the reception time in a communication of one Sync
message. Therefore, a maximum time error of 1.5k μs is included
in the network delay time in a sequence of k Sync messages.
[0100]
15 In view of this, where the predetermined threshold value
at the comparing unit 49 is 1.5k μs, a check can be made to
determine whether there is a variation in network delay time,
with a time error due to a frequency difference being taken
into consideration. For example, where k = 8, the
20 predetermined threshold value at the comparing unit 49 is 12
μs.
[0101]
However, when a variation in network delay time actually
occurs instead of a time error due to a frequency difference,
25 the variation is not detected if the input from the subtracting
unit 48 is slightly smaller than the predetermined threshold
value. As a result, processing is performed on the assumption
that no variations in network delay time have occurred, and
the frequency f2 is not appropriately adjusted.
30 [0102]
Therefore, there is a need for a mechanism for more
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accurately detecting variations that actually occur in network
delay time, instead of time errors due to frequency
differences.
[0103]
In view of this, an example structure 5 of a frequency
difference detection device capable of more accurately
reflecting variations that actually occur in network delay
time through detection of frequency differences is described
next.
10 [0104]
[Fifth Example Structure of the Frequency Difference
Detection Device]
Fig. 11 shows a fifth example structure of the frequency
difference detection device as an embodiment. This frequency
15 difference detection device 60 includes a subtracting unit
61, a (k - 1)-sequence delaying unit 62, a 1-sequence delaying
unit 63, a subtracting unit 64, a dividing unit 65, a switch
66, a subtracting unit 67, a dividing unit 68, a switch 69,
a 1-sequence delaying unit 70, a subtracting unit 71, a
20 determining unit 72, and comparing units 73 and 74.
[0105]
Every time the PTP slave including the frequency
difference detection device 60 receives a Sync message as a
PTP message, the subtracting unit 61 subtracts the transmission
25 time T1i from the reception time T2i, and outputs the difference
T2i - T1i to the (k - 1)-sequence delaying unit 62, the
subtracting unit 64, the subtracting unit 67, the 1-sequence
delaying unit 70, and the subtracting unit 71.
[0106]
30 The (k - 1)-sequence delaying unit 62 stores the
difference T2i - T1i, which is input from the subtracting unit
30
SP335980WO00
61, and outputs the difference T2i-k+1 - T1i-k+1 corresponding
to the Sync message that has been received (k - 1) Sync messages
earlier and been stored, to the 1-sequence delaying unit 63
and the subtracting unit 67. Here, k is an integer of 2 or
greater. For example, k is 8, 5 16, or the like.
[0107]
The 1-sequence delaying unit 63 stores the difference
T2i-k+1 - T1i-k+1, which is input from the (k - 1)-sequence delaying
unit 42, and outputs the difference T2i-k - T1i-k corresponding
10 to the Sync message that has been received k Sync messages
earlier and been stored, to the subtracting unit 64.
[0108]
The subtracting unit 64 subtracts the difference T2i-k
- T1i-k corresponding to the Sync message received k Sync
15 messages earlier from the difference T2i - T1i corresponding
to the Sync message received this time, and outputs the
difference (T2i - T1i) - (T2i-k - T1i-k) = Δm × k - Δs × k =
(Δm - Δs) × k to the dividing unit 65.
[0109]
20 The dividing unit 65 divides the difference (Δm - Δs)
× k, which is input from the subtracting unit 64, by k, and
outputs the frequency difference Δm - Δs obtained as a result
to an input terminal 66a of the switch 66.
[0110]
25 The switch 66 performs switching under the control of
the comparing unit 74, and outputs the value that is input
to an input terminal 51a or an input terminal 51b to the later
stage.
[0111]
30 The subtracting unit 67 subtracts the difference T2i-k+1
- T1i-k+1 corresponding to the Sync message received (k - 1)
31
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Sync messages earlier from the difference T2i - T1i
corresponding to the Sync message received this time, and
outputs the difference (T2i - T1i) - (T2i-k+1 - T1i-k+1) = Δm ×
(k - 1) - Δs × (k - 1) = (Δm - Δs) × (k - 1) to the dividing
5 unit 68.
[0112]
The dividing unit 68 divides the difference (Δm - Δs)
× (k - 1), which is input from the subtracting unit 67, by
(k - 1), and outputs the frequency difference Δm - Δs obtained
10 as a result to an input terminal 69a of the switch 69.
[0113]
The switch 69 performs switching under the control of
the comparing unit 73, and outputs the frequency difference
Δm - Δs, which is input from the dividing unit 46 to the input
15 terminal 69a, or the value 0, which is input to an input terminal
69b to an input terminal 66b of the switch 66.
[0114]
The 1-sequence delaying unit 70 stores the difference
T2i - T1i, which is input from the subtracting unit 61, and
20 outputs the difference T2i-1 - T1i-1 corresponding to the Sync
message that has been received last time and been stored, to
the subtracting unit 71.
[0115]
The subtracting unit 71 subtracts the difference T2i-1
25 - T1i-1 corresponding to the Sync message received last time
from the difference T2i - T1i corresponding to the Sync message
received this time, and outputs the difference (T2i - T1i)
- (T2i-1 - T1i-1) = (T1i-1 - T1i) - (T2i-1 - T2i) = Δm - Δs to
the determining unit 72.
30 [0116]
The determining unit 72 determines the magnitude
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relationship between the input from the subtracting unit 71
or the frequency difference Δm - Δs obtained from one
communication period and a predetermined threshold value.
This predetermined threshold value is 1.5 μs based on the
following 5 assumptions.
[0117]
Assumptions: The frequency variable range of the VCO
of each of the PTP master and the PTP slave is ±300 ppm, each
Sync message transmission interval is 1/64 second, and the
10 largest possible difference between the frequency f2 and the
frequency f1 is 100 ppm. Due to the largest frequency
difference 100 ppm, an error of 1.5 μs (= 100 ppm/64) might
occur in reception time in one Sync message communication.
[0118]
15 The determining unit 72 further notifies the comparators
73 and 74 of an "L", an "S", or an "O" as a determination result.
Specifically, when the frequency difference Δm - Δs is greater
than a predetermined threshold value, the comparing units are
notified of an L. When the frequency difference Δm - Δs is
20 smaller than the predetermined threshold value, the comparing
units are notified of an S. When the frequency difference
Δm - Δs = 0, the comparing units are notified of an O.
[0119]
Fig. 12 shows the meanings of an "L", an "S", and an
25 "O" that are sent from the determining unit 72. An "L"
indicates that the reception time interval Δs between the
current Sync message and the first Sync message in the PTP
slave is longer than a certain length. An "S" indicates that
the reception time interval Δs between the current Sync message
30 and the first Sync message in the PTP slave is shorter than
the certain length. An "O" indicates that the reception time
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interval Δs between the current Sync message and the first
Sync message in the PTP slave is the certain length.
[0120]
Every time a determination result is input from the
determining unit 72, the comparing unit 73 counts 5 and compares
the number CL of "L"s and the number CS of "S"s among the k
-1 determination results up to this time from the determination
result that has been input (k - 1) determination results earlier.
When the number CL of "L"s is equal to the number CS of "S"s,
10 "L"s and "S"s offset each other. Therefore, it is determined
that no variations in network delay time have occurred during
the (k - 1) communication periods, and the switch 69 is made
to switch to the input terminal 69a. When the number CL of
"L"s differs from the number CS of "S"s, it is determined that
15 a variation in network delay time has occurred during the (k
- 1) communication periods, and the switch 69 is made to switch
to the input terminal 69b.
[0121]
Every time a determination result is input from the
20 determining unit 72, the comparing unit 74 counts and compares
the number CL of "L"s and the number CS of "S"s among the k
determination results up to this time from the determination
result that has been input k determination results earlier.
When the number CL of "L"s is equal to the number CS of "S"s,
25 "L"s and "S"s offset each other. Therefore, it is determined
that no variations in network delay time have occurred during
the k communication periods, and the switch 66 is made to switch
to the input terminal 66a. When the number CL of "L"s differs
from the number CS of "S"s, it is determined that a variation
30 in network delay time has occurred during the k communication
periods, and the switch 66 is made to switch to the input terminal
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66b.
[0122]
[Description of Operation]
An operation of the frequency difference detection
device 60 is now described. Fig. 13 5 is a flowchart for
explaining a frequency difference detection process to be
performed by the frequency difference detection device 60.
[0123]
When the PTP slave including the frequency difference
10 detection device 60 receives a Sync message as a PTP message,
the subtracting unit 61 in step S31 subtracts the transmission
time T1i from the reception time T2i, and outputs the difference
T2i - T1i to the (k - 1)-sequence delaying unit 62, the
subtracting unit 64, the subtracting unit 67, the 1-sequence
15 delaying unit 70, and the subtracting unit 71.
[0124]
In step S32, the subtracting unit 64 subtracts the
difference T2i-k - T1i-k, which has been input via the (k -
1)-sequence delaying unit 62 and the 1-sequence delaying unit
20 63 and corresponds to the Sync message received k Sync messages
earlier, from the difference T2i - T1i corresponding to the
Sync message received this time, and outputs the difference
(T2i - T1i) - (T2i-k - T1i-k) = Δm × k - Δs × k = (Δm - Δs) ×
k to the dividing unit 65. The dividing unit 65 divides the
25 difference (Δm - Δs) × k, which has been input from the
subtracting unit 64, by k, and outputs the frequency difference
Δm - Δs as the calculation result (hereinafter referred to
as the first calculation result) to the input terminal 66a
of the switch 66.
30 [0125]
In step S33, the subtracting unit 67 subtracts the
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difference T2i-k+1 - T1i-k+1, which has been input via the (k
- 1)-sequence delaying unit 62 and corresponds to the Sync
message received (k - 1) Sync messages earlier, from the
difference T2i - T1i corresponding to the Sync message received
this time, and outputs the difference (T2i 5 - T1i) - (T2i-k+1
- T1i-k+1) = Δm × (k - 1) - Δs × (k - 1) = (Δm - Δs) × (k -
1) to the dividing unit 68.
[0126]
The dividing unit 68 divides the difference (Δm - Δs)
10 × (k - 1), which has been input from the subtracting unit 67,
by (k - 1), and outputs the frequency difference Δm - Δs as
the calculation result (hereinafter referred to as the second
calculation result) to the input terminal 69a of the switch
69.
15 [0127]
In step S34, the subtracting unit 71 subtracts the
difference T2i-1 - T1i-1, which has been input via the 1-sequence
delaying unit 70 and corresponds to the Sync message received
last time, from the difference T2i - T1i corresponding to the
20 Sync message received this time, and outputs the difference
(T2i - T1i) - (T2i-1 - T1i-1) = (T1i-1 - T1i) - (T2i-1 - T2i) =
Δm - Δs (hereinafter referred to as the third calculation
result) to the determining unit 72.
[0128]
25 In step S35, the determining unit 72 determines the
magnitude relationship between the third calculation result
that has been input from the subtracting unit 71 and a
predetermined threshold value, and notifies the comparators
73 and 74 of an "L", an "S", or an "O" as a determination result.
30 [0129]
In step S36, the comparing unit 74 counts the number
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CL of "L"s and the number CS of "S"s among the k determination
results up to this time from the determination result that
has been input k determination results earlier, and determines
whether the number CL of "L"s is equal to the number CS of
"S"s. If the determination result is positive, 5 the process
moves on to step S37. In step S37, the comparing unit 74 causes
the switch 66 to switch to the input terminal 66a. As a result,
the switch 66 outputs the first calculation result, which has
been input to the input terminal 66a as the frequency difference
10 Δm - Δs, to the later stage.
[0130]
If the determination result in step S36 is negative,
the process moves on to step S38. In step S38, the comparing
unit 74 causes the switch 66 to switch to the input terminal
15 66b. The comparing unit 73 counts the number CL of "L"s and
the number CS of "S"s among the (k - 1) determination results
up to this time from the determination result that has been
input (k - 1) determination results earlier, and determines
whether the number CL of "L"s is equal to the number CS of
20 "S"s. If the determination result is positive, the process
moves on to step S39.
[0131]
In step S39, the comparing unit 73 causes the switch
69 to switch to the input terminal 69a. As a result, the switch
25 69 outputs the second calculation result, which has been input
to the input terminal 69a, to the input terminal 66b of the
switch 66. Having already switched to the input terminal 66b,
the switch 66 outputs the second calculation result, which
has been input to the input terminal 66b, as the frequency
30 difference Δm - Δs to the later stage.
[0132]
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If the determination result in step S38 is negative,
the process moves on to step S40. In step S40, the comparing
unit 73 causes the switch 69 to switch to the input terminal
66b. As a result, the switch 69 outputs the value 0, which
has been input to the input terminal 69b, to 5 the input terminal
66b of the switch 66. Having already switched to the input
terminal 66b, the switch 66 outputs the frequency difference
Δm - Δs = 0 to the later stage.
[0133]
10 In the PTP slave, the oscillation frequency f2 is adjusted
so that the frequency difference Δm - Δs to be output from
the switch 66 will be 0.
[0134]
As described above, the frequency difference detection
15 device 60 detects a variation in network delay time from the
numbers CL and CS of results of determinations performed by
the determining unit 72 on the magnitude relationship with
respect to the predetermined threshold value 1.5 μs.
Accordingly, a variation in network delay time can be detected
20 with higher precision, and frequency synchronization can be
established at a higher speed than with the frequency
difference detection device 40.
[0135]
The frequency difference detection device 60 outputs
25 the frequency difference with respect to the k Sync messages
communication period or the (k - 1) Sync messages communication
period, like the frequency difference detection device 40.
However, frequency differences with respect to communication
periods further including stepwise a (k - 2) Sync messages
30 communication period and a (k - 3) Sync messages communication
period may be detected, for example, and a frequency difference
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not affected by variations in network delay time may be selected
from those frequency differences and be output.
[0136]
[Modification of the Operation of the Frequency
Difference Detection 5 Device 60]
The determining unit 72, the comparing unit 73, and the
comparing unit 74 may be operated as described below.
[0137]
In a case where the frequency difference Δm - Δs obtained
10 by the subtracting unit 71 with respect to one communication
period is 0, the determining unit 72 outputs 0 to the later
stage. In a case where the frequency difference Δm - Δs is
not 0, the determining unit 72 subtracts a predetermined
threshold value (1.5 μs) from the value of the frequency
15 difference, and outputs the subtraction result to the later
stage.
[0138]
Every time 0 or a subtraction result is input from the
determining unit 72, the comparing unit 73 adds up the (k -
20 1) inputs up to this time from the input that has been made
(k - 1) inputs earlier. If the sum is equal to or smaller
than the predetermined threshold value (1.5 μs), it is
determined that no variations in network delay time have
occurred, and the switch 69 is made to switch to the input
25 terminal 69a. If the sum is greater than the predetermined
threshold value (1.5 μs), on the other hand, it is determined
that a variation in network delay time has occurred, and the
switch 69 is made to switch to the input terminal 69b.
[0139]
30 Every time 0 or a subtraction result is input from the
determining unit 72, the comparing unit 74 adds up the k inputs
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up to this time from the input that has been made k inputs
earlier. If the sum is equal to or smaller than the
predetermined threshold value (1.5 μs), it is determined that
no variations in network delay time have occurred, and the
switch 66 is made to switch to the input 5 terminal 66a. If
the sum is greater than the predetermined threshold value (1.5
μs), on the other hand, it is determined that a variation in
network delay time has occurred, and the switch 66 is made
to switch to the input terminal 66b.
10 [0140]
In the case where such an operation is performed, a
variation in network delay time can also be detected with higher
precision, and frequency synchronization can also be
established at a higher speed than with the frequency
15 difference detection device 40.
[0141]
The above described series of processes by the frequency
difference detection devices 10 through 60 can be performed
with hardware or software. Where the series of processes are
20 performed with software, the program that forms the software
is installed into a computer. Here, the computer may be a
computer incorporated into special-purpose hardware, or may
be a general-purpose personal computer that can execute various
kinds of functions as various kinds of programs are installed
25 thereinto.
[0142]
Fig. 14 is a block diagram showing an example structure
of the hardware of a computer that performs the above described
series of processes in accordance with a program.
30 [0143]
In the computer, a CPU (Central Processing Unit) 101,
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a ROM (Read Only Memory) 102, and a RAM (Random Access Memory)
103 are connected to one another by a bus 104.
[0144]
An input/output interface 105 is further connected to
the bus 104. An input unit 106, an output unit 5 107, a storage
unit 108, a communication unit 109, and a drive 110 are connected
to the input/output interface 105.
[0145]
The input unit 106 is formed with a keyboard, a mouse,
10 a microphone, and the like. The output unit 107 is formed
with a display, a speaker, and the like. The storage unit
108 is formed with a hard disk, a nonvolatile memory, or the
like. The communication unit 109 is formed with a network
interface or the like. The drive 110 drives a removable medium
15 111 such as a magnetic disk, an optical disk, a magnetooptical
disk, or a semiconductor memory.
[0146]
In the computer having the above described structure,
the CPU 101 loads a program stored in the storage unit 108
20 into the RAM 103 via the input/output interface 105 and the
bus 104, and executes the program, so that the above described
series of processes are performed.
[0147]
The program to be executed by the computer (the CPU 101)
25 may be recorded on the removable medium 111 as a package medium
to be provided, for example. Alternatively, the program can
be provided via a wired or wireless transmission medium such
as a local area network, the Internet, or digital satellite
broadcasting.
30 [0148]
In the computer, the program can be installed into the
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storage unit 108 via the input/output interface 105 when the
removable medium 111 is mounted on the drive 110. The program
can also be received by the communication unit 109 via a wired
or wireless transmission medium, and be installed into the
storage unit 108. Also, the program 5 may be installed
beforehand into the ROM 102 or the storage unit 108.
[0149]
The program to be executed by the computer may be a program
for performing processes in chronological order in accordance
10 with the sequence described in this specification, or may be
a program for performing processes in parallel or performing
a process when necessary, such as when there is a call.
[0150]
The embodiments of the present disclosure are not limited
15 to the above described embodiments, and various changes may
be made to them without departing from the scope of the present
disclosure.
REFERENCE SIGNS LIST
20 [0151]
10 Frequency difference detection device
11 Subtracting unit
12 1-sequence delaying unit
13 Subtracting unit
25 14 1-sequence delaying unit
15 Selecting unit
16 Adding unit
17 Dividing unit
18 Median filter
30 20 Frequency difference detection device
21 Subtracting unit
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22 1-sequence delaying unit
23 Subtracting unit
24 Comparing unit
25 Switch
30 Frequency difference 5 detection device
31 Subtracting unit
32 k-sequence delaying unit
33 Subtracting unit
34 Dividing unit
10 40 Frequency difference detection device
41 Subtracting unit
42 (k - 1)-sequence delaying unit
43 1-sequence delaying unit
44 Subtracting unit
15 45 Comparing unit
46 Dividing unit
47 Switch
48 Subtracting unit
49 Comparing unit
20 50 Dividing unit
51 Switch
60 Frequency difference detection device
61 Subtracting unit
62 (k - 1)-sequence delaying unit
25 63 1-sequence delaying unit
64 Subtracting unit
65 Comparing unit
66 Switch
67 Subtracting unit
30 68 Dividing unit
69 Switch
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70 1-sequence delaying unit
71 Subtracting unit
72 Determining unit
73, 74 Comparing unit
5
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CLAIMS
1. A frequency difference detection device that detects
a difference in oscillation frequency between a master device
and a slave device connected to each other via a network,
the frequency difference detection 5 device comprising:
a first subtracting unit configured to calculate a
difference between a transmission time T1 contained in a sync
message transmitted periodically from the master device and
a reception time T2 at which the message has been received;
10 a second subtracting unit configured to calculate a
difference between a result of a subtraction T2i - T1i performed
by the first subtracting unit for the sync message received
for the ith time, and a result of a subtraction T2i-k - T1i-k
performed by the first subtracting unit for the sync message
15 received for the (i - k)th time; and
a first dividing unit configured to divide a result of
the subtraction performed by the second subtracting unit by
k.
20 2. The frequency difference detection device according to
claim 1, further comprising:
a third subtracting unit configured to calculate a
difference between the result of the subtraction T2i - T1i
performed by the first subtracting unit for the sync message
25 received for the ith time and a result of a subtraction T2i-k+j
- T1i-k+j performed by the first subtracting unit for the sync
message received for the (i - k + j)th time (j being an integer
smaller than k);
a second dividing unit configured to divide a result
30 of the subtraction performed by the third subtracting unit
by k - j;
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a switch configured to output one of a result of the
division performed by the first dividing unit with k and a
result of the division performed by the second dividing unit
with k - j; and
a switch control unit configured to control 5 the switch.
3. The frequency difference detection device according to
claim 2, wherein, in the slave device, the oscillation
frequency is adjusted to obtain 0 as one of the result of the
10 division performed by the first dividing unit with k and the
result of the division performed by the second dividing unit
with k - j, the one of the results being output from the switch.
4. The frequency difference detection device according to
15 claim 2, wherein, under the control of the switch control unit,
the switch outputs one of the result of the division performed
by the first dividing unit with k, the result of the division
performed by the second dividing unit with k - j, and the value
0.
20
5. The frequency difference detection device according to
claim 4, wherein,
when the absolute value of the result of the subtraction
performed by the second subtracting unit is equal to or smaller
25 than a predetermined threshold value, the switch control unit
causes the switch to output the result of the division performed
by the first dividing unit with k,
when the absolute value of the result of the subtraction
performed by the second subtracting unit is greater than the
30 predetermined threshold value, and the absolute value of the
result of the subtraction performed by the third subtracting
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unit is equal to or smaller than the predetermined threshold
value, the switch control unit causes the switch to output
the result of the division performed by the second dividing
unit with k - j, and,
when the absolute value of the result 5 of the subtraction
performed by the second subtracting unit is greater than the
predetermined threshold value, and the absolute value of the
result of the subtraction performed by the third subtracting
unit is greater than the predetermined threshold value, the
10 switch control unit causes the switch to output the value 0.
6. The frequency detection device according to claim 4,
further comprising:
a fourth subtracting unit configured to calculate a
15 difference between the result of the subtraction T2i - T1i
performed by the first subtracting unit for the sync message
received for the ith time and a result of a subtraction T2i-1
- T1i-1 performed by the first subtracting unit for the sync
message received for the (i - 1)th time; and
20 a determining unit configured to detect an increase,
a decrease, or no variations in network delay time based on
a result of the subtraction performed by the fourth subtracting
unit.
25 7. The frequency difference detection device according to
claim 6, wherein,
when the number of times an increase in the network delay
time has been detected is equal to the number of times a decrease
in the network delay time has been detected among results of
30 the last k detections performed by the determining unit, the
switch control unit causes the switch to output the result
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of the division performed by the first dividing unit with k,
when the number of times an increase in the network delay
time has been detected differs from the number of times a
decrease in the network delay time has been detected among
the results of the last k detections 5 performed by the
determining unit, and the number of times an increase in the
network delay time has been detected is equal to the number
of times a decrease in the network delay time has been detected
among results of the last (k - 1) detections performed by the
10 determining unit, the switch control unit causes the switch
to output the result of the division performed by the second
dividing unit with k - j, and,
when the number of times an increase in the network delay
time has been detected differs from the number of times a
15 decrease in the network delay time has been detected among
the results of the last k detections performed by the
determining unit, and the number of times an increase in the
network delay time has been detected differs from the number
of times a decrease in the network delay time has been detected
20 among the results of the last (k - 1) detections performed
by the determining unit, the switch control unit causes the
switch to output the value 0.
8. A frequency difference detection method implemented in
25 a frequency difference detection device that detects a
difference in oscillation frequency between a master device
and a slave device connected to each other via a network,
the frequency difference detection method comprising:
a first subtracting step of calculating a difference
30 between a transmission time T1 contained in a sync message
transmitted periodically from the master device and a reception
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time T2 at which the message has been received;
a second subtracting step of calculating a difference
between a result of a subtraction T2i - T1i performed in the
first subtracting step for the sync message received for the
ith time, and a result of a subtraction T2i-5 k - T1i-k performed
in the first subtracting step for the sync message received
for the (i - k)th time; and
a dividing step of dividing a result of the subtraction
performed in the second subtracting step by k,
10 the steps being carried out by the frequency difference
detection device.
9. A program to be executed by a computer that detects a
difference in oscillation frequency between a master device
15 and a slave device connected to each other via a network,
the program causing the computer to function as:
a first subtracting unit configured to calculate a
difference between a transmission time T1 contained in a sync
message transmitted periodically from the master device and
20 a reception time T2 at which the message has been received;
a second subtracting unit configured to calculate a
difference between a result of a subtraction T2i - T1i performed
by the first subtracting unit for the sync message received
for the its time, and a result of a subtraction T2i-k - T1i-k
25 performed by the first subtracting unit for the sync message
received for the (i - k)th time; and
a dividing unit configured to divide a result of the
subtraction performed by the second subtracting unit by k.
50