Patent ID: 8750078

Claim:
A slave device used in a system including a master device and the slave device, the slave device comprising: circuitry configured to: output time information; receive messages issued from the master device; issue messages to the master device; calculate a correction value necessary to correct the output time information; and correct the output time information based on the calculated correction value, wherein the circuitry is further configured to: receive a first message that the master device issued at a first time and a second message that contains time information representing the first time and that the master device issued at a time later than the first time; calculate a first correction value by subtracting the first time represented by the time information which is contained in the second message from a second time which is the time at which the first message is received; perform a first stage of correction so that the output time information has a value subtracted by the calculated first correction value; issue a third message to the master device at a third time after the first stage of correction is performed; receive a fourth message that contains time information representing a fourth time at which the third message is received, the fourth message issued by the master device; calculate a second correction value by subtracting the third time at which the third message is issued from the fourth time represented by the time information which is contained in the fourth message and dividing a subtraction result obtained thus by 2; perform a second stage of correction after the first stage of correction is performed so that the output time information has a value added by the calculated second correction value; and increment the output time information by utilizing a counter that is counted up with clocks of a predetermined frequency, and wherein the time information which is contained in the second and fourth messages is a counter value that has not been converted into a unit of seconds.