Tandem Computers Incorporated

Strikumar R Chandran

Mark S Walker

Albert S Lui

Edward J Rhodes

The present invention is an input/output controller for providing total data integrity for any single point failure. The I/O controller comprises a processor module having two microprocessors, an associated memory, a direct memory access module ('DMA'), and a processor support module ('PSM'); a device drive interface; and a channel interface. The two microprocessors are operated in lockstep as a dual modular redundant processor system. The processors provide true and complement, respectively, addresses, data and control strobes. The PSM compares the true and complement data to detect errors (i.e., corresponding data bits not being a true-complement pair) and generates parity protected data (and checks parity) on the data bus. The PSM also generates and checks dual railed control strobes and provides synchronization of all control strobes and interrupt signals to enable the tru-complement pair of microprocessors to operate in lockstep. The DMA compares the redundant addresses from the processors to detect errors and to generate parity protected addresses (and check parity) on the address bus. The DMA also generates the checks bus arbitration signals and controls direct memory access. Self-checking checkers are used to check the various dual railed, true-complement pairs of signals to detect, locate and isolate internal faults. Mis-compares between true-complement address, data and control signals and parity errors detected in reading program instructions from memory all are treated as fatal errors, which cause both processors to halt. Other types of errors are treated as nonfatal, which cause processor exceptions during which appropriate programming is executed to locate and isolate such errors.

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San Jose, CA, United States of America

Strikumar R Chandran