Unisys Corporation

Thomas D Hartnett

John Steven Kuslak

Peter B Criswell

Douglas A Fuller

Wayne D Ward

Gary J Lucas

Leroy J Longworth

David R Schroeder

A method and apparatus to control logic sections of a pipeline instruction processor is disclosed. A state machine is provided that models the flow of instructions through the pipeline. The state machine is capable of modeling execution for all combinations of instruction types that may be present within the pipeline at a given time. The state machine also models various events that affect the way instruction execution is overlapped within the pipeline, and other system occurrences that may cause the termination of some processing activity within the pipeline. The state machine provides signals to control the various logic sections. These signals may be used to determine whether the results of processing activity within the logic sections should be retained or discarded.

Central control system and method for using state information to model inflight pipelined instructions

A synchronous pipeline design is provided that includes a first predetermined number of fetch logic sections, or 'stages', and a second predetermined number of execution stages. Instructions are retrieved from memory and undergo instruction pre-decode and decode operations during the fetch stages of the pipeline. Thereafter, decoded instruction signals are passed to the execution stages of the pipeline, where the signals are dispatched to other execution logic sections to control operand address generation, operand retrieval, any arithmetic processing, and the storing of any generated results. Instructions advance within the various pipeline fetch stages in a manner that may be independent from the way instructions advance within the execution stages. Thus, in certain instances, instruction execution may stall such that the execution stages of the pipeline are not receiving additional instructions to process. This may occur, for example, because an operand required for instruction execution is unavailable. It may also occur for certain instructions that require additional processing cycles. Even though instructions are not entering the execution stages, instructions may continue to enter the fetch stages of the pipeline until all fetch stages are processing a respective instruction. As a result, when normal instruction execution resumes within the execution stages of the pipeline, all fetch stages of the pipeline have been filled, and pre-decode and decode operations have been completed for those instructions awaiting the entry into the execution stages of the pipeline.

Pipeline controller for providing independent execution between the preliminary and advanced stages of a synchronous pipeline

A programmable pipeline depth controller is provided to control the number of instructions that begins execution within an instruction pipeline of an instruction processor within a predetermined period of time. The pipeline depth controller of the present invention includes a logic sequencer responsive to a programmable count value. Upon being enabled, the logic sequencer generates a pipeline control signal to selectively delay the entry of some instructions into the instruction pipeline so that the number of instructions that begins execution within the instruction pipeline during the predetermined period of time following the enabling of the logic sequencer is equal to the count value.

Pipeline depth controller for an instruction processor

A system and method for selectively injecting parity errors into instructions of a data processing system when the instructions are copied from a read buffer to a first level cache. The parity errors are selectively injected according to programmable indicators, each programmable indicator being associated with one or more instructions stored in the read buffer. The error-injection system also includes programmable operating modes whereby error injection will occur during, for example, every copy back from the read buffer to the first level cache, or alternatively, during only a selected copy back sequence. The system allows for comprehensive testing of error detection and recovery logic in an instruction processor, and further allows for comprehensive testing of the logic associated with performing a data re-fetch from a second level cache or storage device.

First level cache parity error inject

Instruction processor and method supporting dual-mode execution of computer instructions. In various embodiments, certain instructions are executable in one of two modes. The first mode is compatible with the native instruction set and data words, and the second mode is an adaptation suitable for platform independent instructions. A control word RAM is addressed by the operation code of an instruction, and each word in the control word RAM includes an address into a microcode RAM. The address into the microcode RAM is manipulated in accordance with the various embodiments to reference either a first set of microcode for native instructions and data words, or a second set of microcode for execution in a platform-independent mode.

Dual microcode RAM address mode instruction execution using operation code RAM storing control words with alternate address indicator

A system and method is provided for selectively injecting interrupts within the instruction stream of a data processing system. The system includes a programmable storage device for storing interrupt injection signals, each of which is associated with a respective machine instruction. When execution of the associated machine instruction is initiated, the stored signal is read from the storage device and is made available to the interrupt logic within the instruction processor. If set to a predetermined logic level, the signal causes an interrupt to be injected within the instruction processor. The system provides the capability to simultaneously inject different types of interrupts, including fault and non-fault interrupts, during the execution of any instruction. The invention further provides a programmable means for injecting errors at predetermined intervals in the instruction stream. Because the current invention allows interrupt injection to be controlled by programmable logic within the instruction processor itself instead by stimulus generated and controlled by a simulation program as in prior art systems, there is no need to develop complex simulation programs to generate and control the external stimulus. Any simulation program can utilize the interrupt injection system to test the interrupt logic. Furthermore, the injected interrupts are handled in a manner which is transparent to the system software, which makes development of test-version interrupt handling code unnecessary. Moreover, the interrupt injection system may be used during normal (non-test) situations to place the instruction processor under microcode control. This can be useful to provide temporary fixes to hardware problems in a manner which is transparent to the operating system.

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Roseville, MN, United States of America

Thomas D Hartnett