International Business Machines Corporation

Other

Motorola Corporation

Charles Roberts Moore

James Allan Kahle

John Stephen Muhich

Robert J Reese

Michael Scott Allen

Hung Qui Le

Terence M Potter

Michael Julio Garcia

Chien-Chyun Lee

Ravi Nair

David James Shippy

Larry Edward Thatcher

Yoanna Baumgartner

Gregory F Grohoski

Wolfram M Sauer

Pradeep Kumar Dubey

Michael C Becker

Tan V Chu

Brian James Vicknair

Edmond J Boufarah

A Storage Reference Buffer (SRB) designed as an autonomous unit for all Store operations that transfer data from the execution unit of a processor to the memory hierarchy and Load operations that transfer data from the memory hierarchy to the execution unit of the processor. The SRB partitions up the Load and Store operations into several smaller operations in order to perform them in parallel with other Load and Store requests. System elements are included to determine unambiguously which of these Load and Store operations may be performed without waiting for prior operations to be completed. The SRB also includes system elements to detect whether requests may be satisfied by existing entries in the SRB without having to access the cache. The SRB is operated as a content addressable memory. Load request are simultaneously launched to cache and to the SRB with the Cache request being canceled if the Load request may be satisfied by an SRB entry.

Managing load and store operations using a storage management unit with data flow architecture

A processor having improved branch prediction accuracy includes at least one execution unit that executes sequential instructions, a condition register, and a branch prediction circuit that predicts a condition register-dependent branch instruction by reference to a potentially stale condition register value to produce a speculative instruction fetch address. In a preferred embodiment, the processor includes branch execution circuitry that subsequently determines if the speculative instruction fetch address is correct by reference to a non-stale value of the condition register.

Processor and method that predict condition register-dependent conditional branch instructions utilizing a potentially stale condition register value

The present invention is a mechanism for providing redundancy in the register file of a microprocessor such that registers having a defective operational status, as determined by testing, can be tolerated and the baseline specification of the microprocessor can be met. The present invention utilizes the register renaming capability of a microprocessor to allow additional registers, above those called for in the specification to be provided. The registers are then tested and those found &ldquo;bad&rdquo; are identified and avoided by the allocation/deallocation logic, which is used to assign registers to the various instructions being executed by the microprocessor. More particularly, the present invention maintains a list of physical registers in a register file that have a functional operational status and are available to be allocated to various instructions as they execute. The allocated registers are typically used to store interim data resulting from the execution of the assigned instruction. When the data in the rename register is complete it is then committed to the architecture by rewriting the results to an architected register. The present invention uses this rename capability to prevent a defective register that was manufactured bad to ever be included in the list of registers that are available for allocation to the processor instructions.

Method and apparatus for utilizing renamed registers based upon a functional or defective operational status of the register

A microprocessor and method of processing instructions for addressing timing assymetries are disclosed. A sequence of instructions including a first instruction and a second instruction are received. Dependency logic determines if any dependencies between the first and second instructions. The dependency logic then selects between first and second issue queue partitions for storing the first and second instructions pending issue based upon the dependency determination, wherein the first issue queue partition issues instructions to a first execution unit and the second issue queue partition issues instructions to a second execution unit. The first and second issue queue partitions may be asymmetric with respect to a first register file in which instruction results are stored. The first and second instructions are then stored in the selected partitions. Selecting between the first and second issue queue partitions may include selecting a common issue queue partition for the first and second instructions if there is a dependency between the first and second instructions and selecting between the first and second issue queue partition may be based upon a fairness algorithm if the first and second instructions lack dependencies.

Partitioned issue queue and allocation strategy

A microprocessor includes a first processor core and a second processor core. The first core includes a first processing block. The first processing block includes an execution unit suitable for executing a first type of instruction. The second core includes a second processing block. The second processing block includes an execution unit suitable for executing an instruction if the instruction is of the first type. The processor further includes a shared execution unit. The first and second processor cores are adapted to forward an instruction to the shared execution unit for execution if the instruction is of a second type. In one embodiment, the first type of instruction includes fixed point instructions, load/store instructions, and branch instructions and the second type of instruction includes floating point instructions.

Shared execution unit in a dual core processor

A processor having improved branch prediction accuracy includes at least one execution unit that executes sequential instructions and a plurality of branch prediction circuits including a lock acquisition branch prediction circuit that predicts a speculative execution path for a conditional branch instruction. The processor further includes a selector that selects the speculative execution path predicted by the lock acquisition branch prediction circuit in response to an indication that the conditional branch instruction is dependent upon lock acquisition. In a preferred embodiment, the indication that the conditional branch instruction is dependent upon lock acquisition is encoded within the conditional branch instruction.

Processor and method for separately predicting conditional branches dependent on lock acquisition

A microprocessor and method of processing instructions therein are disclosed. Initially, a sequence of instructions is dispatched by a dispatch unit of the microprocessor. A code sequence recognition unit (CSR) is configured to detect a short branch sequence within the sequence of instruction, where the short branch sequence includes a condition setting instruction, a conditional branch, and at least one additional instruction that is executed if the conditional branch is not taken. The short branch sequence is then internally converted to a predicated instruction sequence that includes the condition setting instruction and a predicated instruction corresponding to each additional instruction in the short branch sequence. The predicated instruction sequence is then executed in at least one functional unit of the processor. Detecting the short branch sequence may include calculating the relative branch address associated with the conditional branch instruction and comparing the relative branch address to a specified maximum. In one embodiment, the received sequence of instructions may be converted into an instruction group by the processor. In this embodiment, the specified maximum number of instructions in a short branch sequence may be a function of the number of instructions in an instruction group. In an embodiment where the conditional branch statement is preferably allocated to the last slot of the instruction group, the additional instructions in the short branch sequence are located in the next subsequent instruction group. Converting the short branch sequence to the predicated instruction sequence may include converting each additional instruction in the short branch sequence to an analogous predicated instruction. In one embodiment, converting each additional instruction to its analogous predicated instruction includes determining a predicated instruction opcode for each additional instruction in the short branch sequence by adjusting the opcode of each additional instruction by a predetermined offset. In another embodiment, the opcode conversion may be accomplished with an opcode lookup table.

Converting short branches to predicated instructions

A processor having improved branch prediction accuracy includes at least one execution unit that executes sequential instructions and branch processing circuitry that processes branch instructions. The branch processing circuitry includes a number of branch prediction circuits that are each capable of providing a branch prediction for a conditional branch instruction and a selector that selects a branch prediction of a branch prediction circuit based upon the type of condition upon which the conditional branch instruction depends. The selector preferably includes hardware that determines the type of condition upon which the conditional branch instruction depends by reference to an instruction context defined by one or more instructions adjacent the conditional branch instruction in programmed sequence. The branch processing circuitry further includes path address logic that determines a path address of the selected branch prediction. Thus, branch prediction accuracy can be improved by considering the type of condition upon which a conditional branch instruction depends, rather than just branch history.

Branch prediction circuit selector with instruction context related condition type determining

A microprocessor and related method and data processing system are disclosed. The microprocessor includes a dispatch unit suitable for issuing an instruction executable by the microprocessor, an execution pipeline configured to receive the issued instruction, and a pending instruction unit. The pending instruction unit includes a set of pending instruction entries. A copy of the issued instruction is maintained in one of the set of pending instruction entries. The execution pipeline is adapted to record, in response detecting to a condition preventing the instruction from successfully completing one of the stages in the pipeline during a current cycle, an exception status with the copy of the instruction in the pending instruction unit and to advance the instruction to a next stage in the pipeline in the next cycle thereby preventing the condition from stalling the pipeline. Preferably, the dispatch unit, in response to the instruction finishing pipeline execution with an exception status, is adapted to use the copy of the instruction to re-issue the instruction to the execution pipeline in a subsequent cycle. In one embodiment, the dispatch unit is adapted to deallocate the copy of the instruction in the pending instruction unit in response to the instruction successfully completing pipeline execution. The pending instruction unit may detect successful completion of the instruction by detecting when the instruction has been pending for a predetermined number of cycles without recording an exception status. In this embodiment, each entry in the pending instruction unit may include a timer field comprising a set of bits wherein the number of bits in the time field equals the predetermined number of cycles. The pending instruction unit may set, in successive cycles, successive bits in the timer field such that successful completion of an instruction is indicated when a last bit in the time field is set. In one embodiment, pending instruction unit includes a set of copies of instructions corresponding to each of a set of instructions pending in the execution pipeline at any given time. In various embodiments, the execution pipeline may comprise a load/store pipeline, a floating point pipeline, or a fixed point pipeline.

Determining successful completion of an instruction by comparing the number of pending instruction cycles with a number based on the number of stages in the pipeline

A microprocessor includes a fetch unit, an instruction cracking unit, and dispatch and completion control logic. The fetch unit retrieves a set of instructions from an instruction cache. The instruction cracking unit receives the set of fetched instructions and organizes the set of instructions into an instruction group. The dispatch and completion logic assigns a group tag to the instruction group and records the group tag in an entry of the completion table for tracking the completion status of the instructions comprising the instruction group. The dispatch and control logic may record a single instruction address in the completion table entry corresponding to the each instruction group. Preferably, the single instruction address is the instruction address of the first instruction in the instruction group. The processor may flush the instruction group in response to detecting an exception generated by an instruction in the instruction group.

Assigning a group tag to an instruction group wherein the group tag is recorded in the completion table along with a single instruction address for the group to facilitate in exception handling

The present invention is a mechanism for providing redundancy in the instruction buffer of a microprocessor such individual entries which test bad during manufacturing can be tolerated and the baseline specification of the microprocessor can be met. The present invention utilizes the instruction allocation logic of a microprocessor to allow additional buffer entries, above those called for in the specification to be provided. More particularly, each buffer entry is tested and the results are used to identify which individual entry or entries have a defective operational status. This information is then used to update the instruction allocation logic such that functional entries are considered for allocation, while those entries that test bad can be avoided. Further, the test status information can be used to set a &ldquo;manufactured good&rdquo; bit in the entry itself. This bit is then read ultimately by the allocation logic and instructions can be allocated accordingly, i.e. only to those entries which have tested good.

Microprocessor instruction buffer redundancy scheme

A processor and data processing system suitable for dispatching an instruction to an issue unit. The issue unit includes a primary issue queue and a secondary issue queue. The instruction is stored in the primary issue queue if the instruction is currently eligible to issue for execution. The instruction is stored in the secondary issue queue if the instruction is currently ineligible to issue for execution. An instruction may be moved from the primary issue queue to the secondary issue queue if instruction is dependent upon results from another instruction. In one embodiment, the instruction may be moved from the primary issue queue to the secondary issue queue after issuing the instruction for execution. In this embodiment, the instruction may be maintained in the secondary issue queue for a specified duration. Thereafter, the secondary issue queue entry containing the instruction is deallocated if the instruction has not been rejected.

Microprocessor with primary and secondary issue queue

A method and system are efficiently maintaining data coherency in a multiprocessor data processing system having multiple processors coupled together via common bus. Each time an attempted modification is made to selected data by one of the processors, a multistate bus synchronization flag is established within the initiating processor. A bus operation request which is appropriate for the type of data modification is then issued from a cache associated with the initiating processor to a memory queue associated therewith. The bus operation request is then transmitted onto the common bus from the memory queue on an opportunistic basis, permitting additional cache operations to occur during the pendency of the bus operation request. A successful assertion of the bus operation request, indicating no coherency problems exist with respect to other processors, results in an alteration of the state of the multistate bus synchronization flag, permitting modification of the selected data. A failure to successfully assert the bus operation request will result in the automatic reissue of the bus operation request, greatly enhancing the ability of the system to maintain data coherency.

Method and system for efficient maintenance of data coherency in a

A method and system for the enhanced efficiency of data transfers from memory to multiple processors in a data processing system. Each of the multiple processors has an associated buffer for storing data transferred via a common bus which couples the processors and memory together. Each of the multiple processors continually monitors the common bus and is capable of asserting a selected control signal in response to an attempted activity of another one of the multiple processors which would violate data coherency within the data processing system during a particular period of time following the attempted activity. Data is transferred from memory to a buffer associated with one of the multiple processors and stored in the buffer in response to a request from the processor associated with the buffer prior to expiration of the particular period of time and prior to a determination of whether or not this transfer will result in a possible data coherency problem. The common bus is continually monitored during the particular period of time. Transfer of the data from the buffer to the processor is prohibited in response to a presence on the common bus of the selected control signal prior to expiration of the particular of time. Transfer of the data from the buffer to the processor is permitted in response to an absence on the common bus of the selected control signal.

Method and system for enhanced efficiency of data transfers from memory

A method and system are provided for processing instruction threads. Execution is initiated by a processing system of a first set of instructions including a particular instruction. The particular instruction includes an indication of a second set of instructions. In response to execution of the particular instruction and to the processing system being of a first type, the processing system continues executing the first set while initiating execution of the second set. In response to execution of the particular instruction and to the processing system being of a second type, the processing system continues executing the first set without initiating execution of the second set.

Growing community of inventors

Austin, TX, United States of America

Charles Roberts Moore