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

Abstract

A method and apparatus for controlling the flow of data through director elements of a disk drive controller are responsive to external clock signals to synchronize the internal clock timing of each director. The external clock signals are available over either a first master bus or a secondary master bus, each of the buses being connected to the director element. Each director element has circuitry which monitors the occurrence of clock pulses over the buses as well as circuitry for switching, upon the occurrence of a failure of clock pulses on the master bus, from the master bus to the secondary bus for the receipt and resynchronization of clock pulses.