Abstract: A method and apparatus for improving the efficiency of a processor-based emulation engine. The emulation engine is composed of a plurality of processors, each processor capable of emulating a logic gate. Processors are arranged into groups of processors called clusters. Each processor receives inputs, processes the inputs, and stores the outputs in an output array. The output array allows processors within a cluster to fetch an output from a processor that was written to the output array during a previous cycle. The output array can also store and transfer data between clusters of processors. Consequently, the number of cycles that a processor or a cluster has to wait to fetch data is greatly reduced and the efficiency of the emulation engine is increased.

Abstract: The present system and methods are directed to the interconnection of clusters of emulation processors comprising emulation processors in a software-driven hardware design verification system. The processors each output one NBO output signal. The clusters are interconnected by partitioning a common NBO bus into a number of smaller NBO busses, each carrying unique NBO signals but together carrying every NBO. Each of the smaller NBO busses are passed into a series of multiplexers, each dedicated to a particular processor. The multiplexers select a signal for output back to the emulation clusters. The multiplexers that handle these smaller NBO busses are narrower than was previously required, thus reducing the amount of power, interconnect, and area required by the multiplexer array and dedicated interconnect.

Abstract: An instruction processing system and method which utilizes instruction completion to isolate errors, including those in the post-completion processing of operand stores, to an interval between checkpoints, while allowing the processing of checkpointing instructions to be overlapped with that of other instructions. Checkpoints are established before and after such instructions, and all processing (including that of operand stores) from before a checkpoint must be done prior to allowing instruction completion to move beyond the checkpoint. Nevertheless, instructions from beyond a checkpoint are allowed to be processed up to the point of completion while waiting for the checkpoint to be cleared. The point at which instructions must wait on a prior checkpoint is thus moved to the final phase of instruction processing (instruction completion), at significant performance advantage over a conventional implementation in which this waiting is done at instruction fetch, decode, or execution time.

Abstract: An instruction processing system and method which utilizes instruction completion to isolate errors, including those in the post-completion processing of operand stores, to an interval between checkpoints, while allowing the processing of checkpointing instructions to be overlapped with that of other instructions. Checkpoints are established before and after such instructions, and all processing (including that of operand stores) from before a checkpoint must be done prior to allowing instruction completion to move beyond the checkpoint. Nevertheless, instructions from beyond a checkpoint are allowed to be processed up to the point of completion while waiting for the checkpoint to be cleared. The point at which instructions must wait on a prior checkpoint is thus moved to the final phase of instruction processing (instruction completion), at significant performance advantage over a conventional implementation in which this waiting is done at instruction fetch, decode, or execution time.

Abstract: Insures data integrity in process ownership indications by providing an ownership interlock on the data units in a pipeline to a store-in type of cache. An ownership interlock prevents any processor ownership change to occur (i.e. exclusive or readonly ownership) for a cache data unit until all outstanding stores have been made in the cache data unit, after which the ownership may be changed. An ownership change may be signalled by a cross-invalidate (XI) signal to a processor. Outstanding stores are received by the pipeline after the stores are completed by a processor, and the outstanding stores output from the pipeline into a store-in cache. A continuous flow of stores is enabled into and out of the pipeline to expedite a change of ownership requested of a data unit in the cache. The continuous flow avoids having to stop a processor from putting stores into the pipeline and avoids forcing all outstanding stores out of the pipeline into the cache before indicating a change of processor ownership.

Abstract: A system whereby a central processor continues operation beyond a serialization point before the architecture defines that it is permissible to do so. According to the system, it is ascertained whether correct results are being achieved after the serializing point. If some doubt develops about the correctness of the results, the processor is returned to its status at the serialization point and the processing is repeated. In one embodiment, correctness of results is determined by way of a monitoring mechanism which depends on the fact that interactions between CPUs are confined to references to storage. The operations which are performed prior to the time that the architecture allows them, are restricted to ones which depend on fetches made from storage.

Abstract: A method of handling errors in the C bit of a storage key by modifying the INSERT STORAGE KEY (ISK) and the RESET REFERENCE BIT (RRB) instructions. If an error is found in the C bit during the execution of these instructions, microcode is instructed to refresh the C bit. The C bit is interrogated a second time to determine if the refreshed C bit is still in error. If the refreshed C bit is not in error a second time, then the first error was caused by a soft or transient error, and the instruction is continued. If the refreshed C bit is in error a second time then the first and second errors were caused by a permanent error such as a stuck bit, and a system recovery machine check error is generated. The handling of C bit errors is thus done in a dynamic fashion as the instructions are executed.