Abstract: A pipelined, simultaneous and redundantly threaded (“SRT”) processor comprising, among other components, load/store units configured to perform load and store operations to or from data locations such as a data cache and data registers and a cycle counter configured to keep a running count of processor clock cycles. The processor is configured to detect transient faults during program execution by executing instructions in at least two redundant copies of a program thread and wherein false errors caused by incorrectly replicating cycle count values in the redundant program threads are avoided by implementing a cycle count queue for storing the actual values fetched by read cycle count instructions in the first program thread. The load/store units then access the cycle count queue and not the cycle counter to fetch cycle count values in response to read cycle count instructions in the second program thread.

Abstract: A method and system for executing instructions in a computer. Each instruction has a look-ahead code indicating the number of instructions after which may be executed before its own execution is completed. The look-ahead code increments a counter associated with the instruction one past the look-ahead location. The instruction then begins execution. The next instructions will also be cleared to begin execution if they are less than the look-ahead code away from the current instruction. A large number of instructions can thus begin execution and be executing at the same time, thus increasing the speed of the computer operation.

Abstract: A redundantly threaded processor is disclosed having an Active Load Address Buffer (“ALAB”) that ensures efficient replication of data values retrieved from the data cache. In one embodiment, the processor comprises a data cache, instruction execution circuitry, and an ALAB. The instruction execution circuitry executes instructions in two or more redundant threads. The threads include at least one load instruction that causes the instruction execution circuitry to retrieve data from the data cache. The ALAB includes entries that are associated with data values that a leading thread has retrieved. The entries include a counter field that is incremented when the instruction execution circuitry retrieves the associated data value for the leading thread, and that is decremented with the associated data value is retrieved for the trailing thread. The entries preferably also include an invalidation field which may be set to prevent further incrementing of the counter field.

Abstract: An instruction queue is physically divided into two (or more) instruction queues. Each instruction queue is configured to store a dependency vector for each instruction operation stored in that instruction queue. The dependency vector is evaluated to determine if the corresponding instruction operation may be scheduled for execution. Instruction scheduling logic in each physical queue may schedule instruction operations based on the instruction operations stored in that physical queue independent of the scheduling logic in other queues. The instruction queues evaluate the dependency vector in portions, during different phases of the clock. During a first phase, a first instruction queue evaluates a first portion of the dependency vectors and generates a set of intermediate scheduling request signals. During a second phase, the first instruction queue evaluates a second portion of the dependency vector and the intermediate scheduling request signal to generate a scheduling request signal.

Abstract: An optimization scheme used at run-time or compile-time is capable of identifying partially redundant loads and determining whether the load is truly redundant. The truly redundant load may be replaced with a register copy instruction to reduce the memory traffic and save CPU cycle time.

Abstract: Performing hazard detection in a processor that exhibits register latencies between execution units. The opcode classes of producer and consumer instructions are determined. Using these opcode classes, the register latency between the producer and consumer instructions is determined, and a register status signal is sent.

Abstract: One embodiment of the present invention is a computer processor that includes a first scheduler adapted to dispatch a first type of computer instructions, and a second scheduler coupled to the first scheduler and adapted to dispatch a second type of computer instructions. The first type of instructions all have a first latency and the second type of instructions all have a second latency. The first scheduler is skewed relative to the second scheduler so that when the first scheduler dispatches one of the first type of computer instructions having a first latency, the second scheduler will dispatch one of the second type of computer instructions that is dependent on the first type of computer instruction at a time equal to the first latency.

Abstract: A method and apparatus for increasing instruction level parallelism using a buffer pointer assignment scheme is implemented whereby rename buffers are assigned during dispatch even though the physical rename registers may not yet be available. These virtual rename buffers are assigned by a buffer pointer assignment table. A virtual bit implemented along with each of the physical rename registers is flipped when an instruction corresponding to the entry stored within a particular physical rename register is completed and the result written to the architected register. Thus, at dispatch time, rename registers are assigned as if there were more rename buffers than there existed physical rename registers.

Abstract: A reorder buffer is provided which stores a last in buffer (LIB) indication corresponding to each instruction. The last in buffer indication indicates whether or not the corresponding instruction is last, in program order, of the instructions within the buffer to update the storage location defined as the destination of that instruction. The LIB indication is included in the dependency checking comparisons. A dependency is indicated for a given source operand and a destination operand within the reorder buffer if the operand specifiers match and the corresponding LIB indication indicates that the instruction corresponding to the destination operand is last to update the corresponding storage location. At most one of the dependency comparisons for a given source operand can indicate dependency. According to one embodiment, the reorder buffer employs a line-oriented configuration.

Abstract: A register renaming system for out-of-order execution of a set of reduced instruction set computer instructions having addressable source and destination register fields, adapted for use in a computer having an instruction execution unit with a register file accessed by read address ports and for storing instruction operands. A data dependence check circuit is included for determining data dependencies between the instructions. A tag assignment circuit generates one of more tags to specify the location of operands, based on the data dependencies determined by the data dependence check circuit. A set of register file port multiplexers select the tags generated by the tag assignment circuit and pass the tags onto the read address ports of the register file for storing execution results.

Abstract: A method for associating subroutine calls with corresponding targets includes the step of maintaining a first table of entries. Each entry in the first table includes: a first table first address identifying an entry point address for a corresponding subroutine; and a first table second address identifying a return address of a return for the corresponding subroutine. A second table of entries is also maintained. Each entry in the second table includes: a second table first address identifying a return address of a return for a respective subroutine called by a corresponding subroutine call instruction; a second table second address identifying a target address of the return for the respective subroutine; and a second table third address identifying an entry point address for the respective subroutine. It is determined whether the second table stores an entry whose second table first address corresponds to a return address of a return for a considered subroutine.

Abstract: A method and circuit is disclosed for tagging and invalidating speculatively executed instructions. The method includes fetching a first plurality of instructions which includes a conditional branch instruction which identifies a target address if the branch is taken. The conditional branch instruction is detected and in response thereto first and second instruction tags are generated. At least a first instruction is tagged with the first instruction tag wherein the first instruction is included in the first plurality of instructions and wherein the first instruction sequentially follows the first conditional branch instruction in program order. Thereafter, a second plurality of instructions are fetched wherein the second plurality of instructions corresponds to the target address of the conditional branch instruction. At least one of these second plurality of instructions is tagged with the second instruction tag. Thereafter, the conditional branch instruction is executed and resolved.

Abstract: A computer apparatus incorporating special instructions to force load and store operations to execute in program order. The present invention provides a new and novel store instruction that is suspended until all prior store instructions have been completed by an associated CPU. Also, a new load instruction is provided which blocks any subsequent load instructions from executing until this load instruction has been completed by an associated CPU. These instructions allow for high efficiency computer systems to be implemented which optimize instruction throughput by executing subsequent instructions while waiting for a prior instruction to complete.

Abstract: A method for structuring a multi-instruction computer program as containing a plurality of basic blocks, that each compose from internal instructions and external jumps organised in an internal directed acyclic graph. A guarding is executed on successor instructions that each collectively emanate from a respectively associated single predecessor instruction. A subset of joined instructions that converge onto a single join/target instruction are then unconditionally joined. This is accomplished by letting each respective instruction in the subset of joined instructions be executed under mutually non-related conditions, specifying all operations with respect to a jump instruction, specifying all operations that must have been executed previously, and linking various basic blocks comprising subsets of successor instructions in a directed acyclic graph which allows parallel execution of any further subset of instructions contained therein.

Abstract: In one aspect the present invention provides for an apparatus that includes at least two physical registers and a rename unit to assign at least one of the physical registers to an original register. The original register appears as a destination address in a micro-op. The apparatus includes a rename table having a location for recording the assigned physical register to the original register. The location has at least one bit for indicating whether the assigned physical register belongs to a first or a second class. The rename table is connected to the rename unit and is adapted to lookups of the assigned physical register.

Abstract: A processor employing a dependency link file. Upon detection of a load which hits a store for which store data is not available, the processor allocates an entry within the dependency link file for the load. The entry stores a load identifier identifying the load and a store data identifier identifying a source of the store data. The dependency link file monitors results generated by execution units within the processor to detect the store data being provided. The dependency link file then causes the store data to be forwarded as the load data in response to detecting that the store data is provided. The latency from store data being provided to the load data being forwarded may thereby be minimized. Particularly, the load data may be forwarded without requiring that the load memory operation be scheduled.

Abstract: An apparatus including a set of data storage units having a set of scoreboard bits associated with the set of data storage units; a first execution unit having an output coupled to the data storage unit and a first input; a first switching unit having an output coupled to the first input of the first execution unit and a first input coupled to the output of the first execution unit; and, a first bypass control unit coupled to the first switching unit. The first bypass control unit is configured to cause the first switching unit to couple the output of the first switching unit to the first input of the first switching unit based upon the set of scoreboard bits.

Abstract: A method and system in an information processing system are disclosed for efficiently maintaining copies of values stored within a plurality of registers. The information processing system includes first circuitry, second circuitry, and a plurality of buffers. The first circuitry processes an execution state of a first type of instruction which always specifies a destination of at least one of a first type of register or a second type of register, and which outputs first information in response thereto. The first circuitry also processes an execution stage of a second type of instruction which always specifies a destination of only a third type of register, and outputs second information in response thereto.

Abstract: An instruction fetch unit 10 issues a normal ALU operating instruction or a wide ALU operating instruction using two operating units to a first pipeline 14. The instruction fetch unit 10 also issues a normal ALU operating instruction to a second pipeline 16. Occasionally, a wide ALU operating instruction using both a first integer unit 20 and a second integer unit 24 to the first pipeline 14 while a normal ALU operating instruction using the second integer unit 24 to the second pipeline 16. In this case, if the normal ALU operating instruction is earlier, then the normal ALU operating instruction is executed preferentially. If the wide ALU operating instruction is earlier, then the wide ALU operating instruction is executed preferentially.

Abstract: A microprocessor having an instruction queue capable of out-of-order instruction dispatch and rapidly selecting one or more oldest eligible entries is disclosed. The microprocessor may comprise a plurality of instruction execution pipelines, an instruction cache, and an instruction queue coupled to the instruction cache and execution pipelines. The instruction queue may comprise a plurality of instruction storage locations and may be configured to output up to a predetermined number of non-sequential out of order instructions per clock cycle. The microprocessor may be further configured with high speed control logic coupled to the instruction queue. The control logic may comprise a number of pluralities of multiplexers, wherein the first plurality of multiplexers are configured to select a first subset of the instructions stored in the queue. The second plurality of multiplexers then select a second subset of instructions from the first subset.

Abstract: In one embodiment, a processor includes thread management logic including a thread predictor having state machines to indicate whether thread creation opportunities should be taken or not taken. The processor includes a predictor training mechanism to receive retired instructions and to identify potential threads from the retired instructions and to determine whether a potential thread of interest meets a test of thread goodness, and if the test is met, one of the state machines that is associated with the potential thread of interest is updated in a take direction, and if the test is not met, the state machine is updated in a not take direction. The thread management logic may control creation of an actual thread and may further include reset logic to control whether the actual thread is reset and wherein if the actual thread is reset, one of the state machines associated with the actual thread is updated in a not take direction.

Abstract: A reorder buffer is configured into multiple lines of storage, wherein a line of storage includes sufficient storage for instruction results regarding a predefined maximum number of concurrently dispatchable instructions. A line of storage is allocated whenever one or more instructions are dispatched. A microprocessor employing the reorder buffer is also configured with fixed, symmetrical issue positions. The symmetrical nature of the issue positions may increase the average number of instructions to be concurrently dispatched and executed by the microprocessor. The average number of unused locations within the line decreases as the average number of concurrently dispatched instructions increases. One particular implementation of the reorder buffer includes a future file. The future file comprises a storage location corresponding to each register within the microprocessor.

Abstract: According to the present invention, a system for reordering commands to achieve an optimal command sequence based on a target response restriction is disclosed. A data queue coupled to a command queue is arranged to store a time indicating when the data transfer will appear on the data bus between the controller for an already issued request to the target device as well as arranged to store the burst bit and the read/write bit (r/w). The system also includes a collision detector coupled to the data queue and the command queue arranged to detect the possible collisions on the data bus between the issued command that is stored in the command queue and already issued commands that are stored in the data queue. A queues and link controller is coupled to the collision detector and the data queue and the command queue and is arranged to store and reorder commands to be issued wherein the controller calculates the new issue time of commands as well as a time when the data appears on the data bus.

Abstract: A processor employs ordering dependencies for load instruction operations upon store address instruction operations. The processor divides store operations into store address instruction operations and store data instruction operations. The store address instruction operations generate the address of the store, and the store data instruction operations route the corresponding data to the load/store unit. The processor maintains a store address dependency vector indicating each of the outstanding store addresses and records ordering dependencies upon the store address instruction operations for each load instruction operation. Accordingly, the load instruction operation is not scheduled until each prior store address instruction operation has been scheduled. Store addresses are available for dependency checking against the load address upon execution of the load instruction operation. If a memory dependency exists, it may be detected upon execution of the load instruction operation.

Abstract: A superscalar computer architecture for executing instructions out-of-order, comprising a multiplicity of execution units, a plurality of registers, and a register renaming circuit which generates a list of tags corresponding to specific registers that are not in use during loading of a given instruction. A table is constructed having one bit for each register per instruction in flight. The entries in the table may be combined in a logical OR fashion to create a vector that identifies which registers are in use by instructions that are in flight. Validity bits can also be generated to indicate validity of the generated tags, wherein a generated tag is invalid only if an insufficient number of registers are available during loading of the given instruction. The execution units are preferably pipelined.

Abstract: A processor employs an instruction queue and dependency vectors therein which allow a flexible dependency recording structure. The dependency vector includes a dependency indication for each instruction queue entry, which may provide a universal mechanism for scheduling instruction operations. An arbitrary number of dependencies may be recorded for a given instruction operation, up to a dependency upon each other instruction operation. Since the dependency vector is configured to record an arbitrary number of dependencies, a given instruction operation can be ordered with respect to any other instruction operation. Accordingly, any architectural or microarchitectural restrictions upon concurrent execution or upon order of particular instruction operations in execution may be enforced. The instruction queues evaluate the dependency vectors and request scheduling for each instruction operation for which the recorded dependencies have been satisfied.

Abstract: Storage access blocking instructions, such as the EIEIO instruction implemented within the PowerPC architecture, block other storage access instructions at the bus interface stage as opposed to the execute stage. Therefore, cacheable instructions, and other similar instructions, are allowed to complete without being blocked by such an EIEIO instruction not ordered by the EIEIO instruction.

Abstract: The existing execution units of a high-performance processor are augmented by tile addition of a supplemental integer execution unit, termed the Add/Move Unit (AMU), which performs select adds and moves in parallel and out-of-order with respect to the other execution units. At small incremental cost, AMU enables better use of the expensive limited resources of an existing Address Preparation unit (AP), which handles linear and physical address generation for memory operand references, control transfers, and page crosses. AMU removes data dependencies and thereby increases the available instruction level parallelism. The increased instruction level parallelism is readily exploited by the processor's ability to perform out-of-order and speculative execution, and performance is enhanced as a result.

Abstract: A microprocessor capable of out-of-order instruction decoding and in-order dependency checking is disclosed. The microprocessor may include an instruction cache, two decode units, a reorder queue, and dependency checking logic. The instruction cache is configured to output cache line portions to the decode units. The decode units operate independently and in parallel. One of the decode units may be a split decoder that receives all instruction bytes from instructions that extend across cache line portion boundaries. The split decode unit may be configured to reassemble the instruction bytes into instructions. These instructions are then decoded by the split decode unit. A reorder queue may be used to store the decoded instructions according to their relative cache line positions. The decoded instructions are read out of the reorder queue in program order, thereby enabling the dependency checking logic to perform dependency checking in program order.

Abstract: The present invention is directed to method and apparatus for reordering load operations in a computer processing system.

Abstract: A superscalar microprocessor includes a reorder buffer to correctly handle dependency checking and multiple updates to the same destination. The reorder buffer stores instructions in program order, and retires instructions that have executed and the results obtained. When a instruction is retired, the results of the instruction are stored and the memory space in the reorder buffer is deallocated. The results of the retired instructions are stored to a register file via a retire bus. If the results of two or more retired instructions output to the same register in the register file, then only the newest instruction, the later instruction in the original program sequence, is stored to the program register. The register file has a plurality of write ports for the transfer of data via the retire bus. If two retired instructions output to the same register, then a write port is not utilized. The retire window is the number of instructions monitored for retirement.

Abstract: The present invention discloses a method and apparatus for matching data types of operands in an instruction. A type code of an operand used by the instruction is determined. An attribute value of a storage element which corresponds to the operand is read from a speculative array. This attribute value is then compared with the type code.

Abstract: In one embodiment of the invention, a processor includes an execution pipeline to concurrently execute at least portions of threads, wherein at least one of the threads is dependent on at least another one of the threads. The processor also includes detection circuitry to detect speculation errors in the execution of the threads. In another embodiment, the processor includes thread management logic to control dynamic creation of threads from a program.

Abstract: A very long instruction word (VLIW) processor exploits program level parallelism as well as instruction level parallelism. Unlike prior VLIW machines which obtain speed advantages using instruction level parallelism, the present processor exploits the parallelism inherent in a VLIW processor by providing new instruction level mechanisms to separate processor execution into parallel threads. This separation allows greater hardware use because more than one program can exploit instruction level parallelism on the system at the same time. A first program and a second program execute concurrently such that the second program executes using resources and cycles that would have been wasted by the first program. This construct is especially useful where the second program is an interrupt service routine because the interrupt service routine can be threaded through the machine with high or low priority while the functional units still process the first program stream.

Abstract: Instruction issue logic is disclosed that assesses register availability. The issue logic comprises register scoreboard logic that includes destination register storage elements to identify destination registers of instructions queued for issue. An arbiter selects instructions for issue during a machine cycle from the queued instructions. Register-clean wires associated with each register are driven in response to the corresponding destination storage elements and the arbiter. These wires are used to identify the read-availability of registers. Specifically, such a logic system is capable of reflecting freed registers on the subsequent machine cycle so that previously issued instructions do not hinder queuing of new instructions, unless they require multiple cycles to complete. To increase speed of operation, single NMOS devices bridge the register-clean wires and the issue signal from the arbiter.

Abstract: An event notification system for a network including a managed device that includes one or more management agents that detect one or more management events of a plurality of possible management events. The managed device further includes event notification logic that generates an event notification message (ENM) which includes event related information. The ENM is written using a markup language, such as XML, to encode the event related information based on the management event. The ENM may include executable code written in a scripting language or the like, that when executed, causes at least one action to be performed. A management server is provided that includes an event processor that executes the code to perform the desired actions in response to the particular management event. The event related information may further include a URL to locate one or more information files in the network that provides further information about the management event.

Abstract: Two instruction executions circuits C1 and C2, possibly pipelined, share a write port to write instruction results to their destinations. When both circuits have results available for writing in the same clock cycle, the write port is given to circuit C1. Circuit C2 gets the write port only when there is a bubble in the write back stage of circuit C1. Circuit C2 executes instructions that occur infrequently in an average program. Examples are division, reciprocal square root, and power computation instructions. Circuit C1 executes instructions that occur more frequently. Circuits C1 and C2 are part of a functional unit of a VLIW processor.

Abstract: A method and computer program product are provided for paging control using a reference structure in a computer system. The reference structure is scanned to identify a next selected entry for an IO range building routine. The next selected entry is compared with a set hardlimit value. Responsive to the next selected entry being greater than the hardlimit value, the IO range building routine is exited. A shortlimit value is identified. The next selected entry is compared with the identified shortlimit value. Responsive to the next selected entry being greater than the identified shortlimit value, the IO range building routine is exited. A first array is used for storing entry IDs for selected entries found from scanning the reference structure and a second array is used for tracking blocks of storage used for the selected entries.

Abstract: An apparatus is provided for collecting state information associated with an execution path of recently processed instructions in a processor pipeline of a computer system. The apparatus identifies a class of instructions to be sampled. Path-identifying state information of a currently processed instruction is sampled when the currently processed instruction belongs to the identified class of instructions. A shift register stores a predetermined number of entries storing selected state information, the shift register is simultaneously sampled along with additional state information about the instruction being executed at the time of sampling.

Abstract: Embodiments of the present invention provide a stack renaming method and apparatus for stack based processors. Using principles of the present invention, a stack can be accessed simultaneously by one or more functional units in a stack processor. The stack apparatus includes a stack renaming unit capable of renaming a logical stack address to a real stack address. Each logical stack address corresponds to a storage element in the stack renaming unit which stores a real stack address. A circular counter is used in the stack renaming unit to sequentially cycle through each of the logical stack addresses. The real stack addresses corresponding to each of the logical stack addresses can be stored out of order in the stack renaming unit. A stack control unit is coupled to the stack renaming unit and provides one or more control signals to the stack renaming unit and coordinates the operation of the stack renaming unit within the stack apparatus.

Abstract: A system and method for performing register renaming of source registers in a processor having a variable advance instruction window for storing a group of instructions to be executed by the processor, wherein a new instruction is added to the variable advance instruction window when a location becomes available. A tag is assigned to each instruction in the variable advance instruction window. The tag of each instruction to leave the window is assigned to the next new instruction to be added to it. The results of instructions executed by the processor are stored in a temp buffer according to their corresponding tags to avoid output and anti-dependencies. The temp buffer therefore permits the processor to execute instructions out of order and in parallel. Data dependency checks for input dependencies are performed only for each new instruction added to the variable advance instruction window and register renaming is performed to avoid input dependencies.

Abstract: A microprocessor comprises a plurality of instruction pipelines having a plurality of stages for processing a stream of instructions, circuitry for simultaneously issuing instructions into two or more of the pipelines without regard to whether one of the simultaneously issued instructions has a data dependency on other of the simultaneously issued instructions, detecting circuitry for detecting dependencies between instructions in the pipelines and circuitry for controlling the flow of instructions through the pipelines such that an instruction is not delayed due to a data dependency on another instruction unless the data dependency must be resolved for proper processing of the instruction in its current stage.

Abstract: A reorder buffer is configured into multiple lines of storage, wherein a line of storage includes sufficient storage for instruction results regarding a predefined maximum number of concurrently dispatchable instructions. A line of storage is allocated whenever one or more instructions are dispatched. A microprocessor employing the reorder buffer is also configured with fixed, symmetrical issue positions. The symmetrical nature of the issue positions may increase the average number of instructions to be concurrently dispatched and executed by the microprocessor. The average number of unused locations within the line decreases as the average number of concurrently dispatched instructions increases. One particular implementation of the reorder buffer includes a future file. The future file comprises a storage location corresponding to each register within the microprocessor.

Abstract: An on-chip breakpoint unit of an integrated circuit device is connected to receive the contents of an instruction pointer register via an address communication path. The breakpoint unit has a breakpoint register configured to hold a breakpoint address at which the normal operation of the CPU is to be interrupted for diagnostic purposes, and a comparator circuit operative to compare the breakpoint address with the contents of the instruction pointer register and to issue a breakpoint signal on a breakpoint signal path when there is a match. The on-chip breakpoint unit also has circuitry configured to inhibit generation of the breakpoint signal for a next instruction to be executed upon resumption of normal operation of the CPU after it has been interrupted.

Abstract: Herein disclosed is a microcomputer MCU adopting the general purpose register method. The microcomputer is enabled to have a small program capacity or a high program memory using efficiency and a low system cost, while enjoying the advantage of simplification of the instruction decoding as in the RISC machine having a fixed length instruction format of the prior art, by adopting a fixed length instruction format having a power of 2 but a smaller bit number than that of the maximum data word length fed to instruction execution means. And, the control of the coded division is executed by noting the code bits.

Abstract: An optimized storage system is implemented in a processor that executes instructions out of order. The system minimizes storage requirements for dependency operands in the processor by eliminating a need for separate storage mechanisms for holding different dependency operands that are produced from different instructions. The system comprises the following elements. An instruction reordering mechanism is configured to permit execution of the instructions in an out of order sequence. Rename registers (RRs) are associated with the reordering mechanism. Logic causes storage of trap information in the rename registers intermixed with instruction execution results. The trap information may be associated with arithmetic integer or floating point (fp) operations and can include the identity of the trapped instruction, the trapped operation, etc. Logic further causes storage of different sized dependency operands within the RRs.

Abstract: An instruction queue is physically divided into two (or more) instruction queues. Each instruction queue is configured to store a dependency vector for each instruction operation stored in that instruction queue. The dependency vector is evaluated to determine if the corresponding instruction operation may be scheduled for execution. Instruction scheduling logic in each physical queue may schedule instruction operations based on the instruction operations stored in that physical queue independent of the scheduling logic in other queues. The instruction queues evaluate the dependency vector in portions, during different phases of the clock. During a first phase, a first instruction queue evaluates a first portion of the dependency vectors and generates a set of intermediate scheduling request signals. During a second phase, the first instruction queue evaluates a second portion of the dependency vector and the intermediate scheduling request signal to generate a scheduling request signal.

Abstract: A non-aligned double word fetch buffer is integrated into a digital signal processor to handle non-aligned double word (32 bit) fetches. When a misaligned double word fetch is detected, the buffer causes a two cycle non-interruptable instruction to be initiated. The first cycle is a 16-bit misaligned data fetch. The address pointer is incremented by 2 and stored in a temporary pointer register. The second cycle is a 32-bit double word fetch based on the temporary pointer with its least significant bit set to 0 (an aligned fetch). The low word from this fetch is used to satisfy the current misaligned double word fetch and the high word is stored in a temporary buffer register in case it proves useful in subsequent misaligned double fetch instructions. Finally, the temporary address pointer is incremented by 2 for possible use in subsequent misaligned fetches.

Abstract: A processor includes a lookahead address/result calculation unit which is configured to receive operand information (either the operand or a tag identifying the instruction which will produce the operand value) corresponding to the source operands of one or more instructions. If the operands are available, lookahead address/result calculation unit may generate either a lookahead address for a memory operand of the instruction or a lookahead result corresponding to a functional instruction operation of the instruction. The lookahead address may be provided to a load/store unit for early initiation of a memory operation corresponding to the instruction. The lookahead result may be provided to a speculative operand source (e.g. a future file) for updating therein. A lookahead state for a register may thereby be provided early in the pipeline. Subsequent instructions may receive the lookahead state and use the lookahead state to generate additional lookahead state early.

Abstract: A method of scheduling program instructions for execution in a computer processor comprises fetching and holding instructions from an instruction memory and executing the fetched instructions out of program order. When load/store order violations are detected, the effects of the load operation and its dependent instructions are erased and they are re-executed. The load is associated with all stores on whose data the load depends. This collection of stores is called a store set. On a subsequent issuance of the load, its execution is delayed until any store in the load's store set has issued. Two loads may share a store set, and separate store sets are merged when a load from one store set is found to depend on a store from another store set. A preferred embodiment employs two tables. The first is a store set ID table (SSIT) which is indexed by part of, or a hash of, an instruction PC.