Master apparatus and slave apparatus and time-synchronization method

A slave apparatus which is connected to a master apparatus via a transmission path and performs time-synchronization with the master apparatus, comprising:

• a sequence executing circuit that repeatedly executes with the master apparatus an offset value calculation notification sequence which includes a data transmission/reception for calculating an offset value for correcting a transmission path delay, and a reception of a notification of the offset value calculated in the master apparatus;
• a first data receiving circuit that receives, every time the offset value calculation notification sequence is executed, first sequence identifier notification data for notifying a sequence identifier, which is an identifier of the offset value calculation notification sequence, transmitted from the master apparatus;
• an offset value storing circuit that stores the offset value notified in the offset value calculation notification sequence in relation to the sequence identifier of the offset value calculation notification sequence notified in the first sequence identifier notification data, the offset value storing section storing a plurality of offset values;
• a second data receiving circuit that receives second selected sequence identifier notification data transmitted from the master apparatus for notifying a selected sequence identifier by the master apparatus;
• and
• an offset value managing circuit that selects, as the offset value used for the time-synchronization with the master apparatus, one of the plurality of offset values previously stored in the offset value storing circuit, the one of the plurality of offset values selected corresponding to the selected sequence identifier notified in the second sequence identifier notification data,
• wherein the offset value managing circuit selects the one of the plurality of offset values previously stored in response to detection of instability in the transmission path delay.

A time-synchronization method performed with a plurality of slave apparatuses by a master apparatus connected to the plurality of slave apparatuses via a transmission path, comprising:

• repeatedly executing an offset value calculation notification sequence in which an offset value for correcting a transmission path delay is calculated after communications with the plurality of slave apparatuses, the offset value calculated is notified to the plurality of slave apparatuses;
• notifying the plurality of slave apparatuses, every time the offset value calculation notification sequence is executed, of a sequence identifier which is an identifier for the offset value calculation notification sequence;
• and
• selecting a sequence identifier from among sequence identifiers previously notified to the plurality of slave apparatuses, notifying the plurality of slave apparatuses of a selected sequence identifier, and instructing the plurality of slave apparatuses to use, for the time-synchronization, an offset value notified in the offset value calculation notification sequence corresponding to the selected sequence identifier,
• wherein the sequence identifier from the sequence identifies previously notified is selected in response to detection of instability in the transmission path delay.

A time-synchronization method performed with a master apparatus by a slave apparatus connected to the master apparatus via a transmission path, comprising:

• repeatedly executing, with the master apparatus, an offset value calculation notification sequence including data transmission/reception to calculate an offset value for correcting a transmission path delay, and reception of a notification of the offset value calculated in the master apparatus;
• receiving, every time the offset value calculation notification sequence is executed, first sequence identifier notification data for notifying a sequence identifier which is an identifier of the offset value calculation notification sequence, transmitted from the master apparatus;
• storing the offset value notified in the offset value calculation notification sequence in relation to the sequence identifier of the offset value calculation notification sequence notified in the first sequence identifier notification data, a plurality of offset values being stored;
• receiving second selected sequence identifier notification data transmitted from the master apparatus for notifying a selected sequence identifier by the master apparatus;
• and
• selecting, as the offset value used for the time-synchronization with the master apparatus, one of the plurality of offset values stored, the one of the plurality of offset values stored corresponding to the selected sequence identifier notified in the second sequence identifier notification data,
• wherein the one of the plurality of offset values previously stored is selected in response to detection of instability in the transmission path delay.