Patent ID: 8140918

Claim:
A clock supply method for supplying a clock to a plurality of processing units, comprising: supplying a clock from a first clock supply unit to first processing units forming a first group among the plurality of processing units as a primary clock and to second processing units forming a second group among the plurality of processing units as a standby clock; supplying a clock from a second clock supply unit including a clock source different from a clock source of the first clock supply unit to the second processing units as a primary clock and to the first processing units as a standby clock; and switching, when one of the first processing units or one of the second processing units detects an abnormality of its primary clock, the standby clock into use in place of the primary clock being supplied to the one of the first and second processing units for which the abnormality of the primary clock is detected, wherein the first and second clock supply units supply clocks with the same frequency and none of the plurality of processing units belong to both of the first and second groups at the same time.