A hierarchal organization of registers containing error indicators is utilized to determine which of a plurality of error recovery modules is to be executed. A redundancy mask and a priority mask stored in a data table associated with each register are sequentially applied to each register in order to eliminate redundant error indicators resulting from a common fault and to set the order of execution of error recovery modules. Thus, the redundancy and priorities associated with detected errors can be controlled substantially independent of the actual error recovery actions to be taken.

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.

A method A and apparatus for monitoring and switching over from a primary bus to a back-up bus in a network having a master node and at least one slave node, the primary bus and the back-up bus each interconnecting the master node and the at least one slave node. The method includes periodically sending via the back-up bus from the master node to each of the slave nodes a master test packet containing a master address of the master node on the back-up bus and sending on the back-up bus from the at least one slave node to the master node and in response to receiving the master test packet, a slave test packet containing a slave address of the at least one slave node on the back-up bus. The method further includes indicating failures on the primary and back-up bus and disconnecting the primary bus from the master node and the at least one slave node and resuming communications between the master node and the at least one slave node via the back-up bus when a failure occurs on the primary bus and no failures occur on the back-up bus.

A method of requesting data in a data processing system has the steps of receiving a plurality of requests for data by a request arbitrator (12) from a plurality of requesters (REQUESTER A, REQUESTER B, REQUESTER C), requesting a first portion of each request at a first time and requesting a second portion of each request at a second time. Each of the requests for data corresponds to a first portion of data. At least one of the requests also corresponds to a second portion of data. The first portions and second portion are requested according to a first and to a second predetermined order, respectively. The disclosed method requests a critical mount of data first for each request before any non-critical data portions are requested.

A method and apparatus for coupling a signal from one node to another node prepares a signal for transmission, performs error checking on such signal while simultaneously transferring such signal within a transmitting node, transmits the signal from the transmitting node, receives and formats the signal at a receiving node, including an identifying portion and a data portion, and directly stores the data portion in memory that is directly accessible by a user process executing in the receiving node while simultaneously performing error checking.