Disk drive controller for controlling data flow therethrough by switching to secondary bus to receive clock pulses when a failure on master bus is detected

A method for controlling the flow of data through directors of a disk drive controller, the directors being responsive to external clock signals to synchronize the internal clock timing of the directors comprising:

• connecting a master bus and a secondary bus to each director;
• monitoring the occurrence of clock pulses over the buses;
• incrementing, at each director, a counter responsive to each received clock pulse from the buses;
• selecting from which bus to receive clock pulse;
• identifying a first low threshold failure of clock pulses on the master bus;
• effecting a synchronization event in response to the threshold failure wherein the counter is reset;
• deciding, at each director, whether to cause the director to switch to the secondary bus for receiving clock pulses;
• and
• switching from the master bus to the secondary bus for the receipt of clock pulses by the directors upon the occurrence of a failure of clock pulses over the master bus.

A disk drive controller for interconnecting a host computer to a plurality of disk drives, such controller comprising:

• a global memory;
• a plurality of directors each one being coupled to the global memory, each one of the directors having:
• an internal clock;
• a counter;
• and a microprocessor;
• a pair of clock lines, each one of the plurality of directors being coupled to the pair of clock lines, one of such pair of clock lines being initially designated as a primary clock line and the other being a secondary clock line, one of the plurality of directors being initially designated as a source for producing clock pulses on the primary clock line for the plurality of directors;
• wherein directors increment the internal counter thereof for counting the clock pulses on the primary clock line, and wherein the microprocessor therein determines whether the count has reached a predetermined value after a predetermined period of time, and if not, a synchronization event is declared;
• and
• wherein, in response to the declared synchronization event and upon agreement among the plurality of directors, a different one of the directors is selected to produce clock pulses for the plurality of directors on the secondary clock line.