Cadence Design Systems, Inc.

Oracle America, Inc.

Oracle International Corporation

Western Digital Technologies, Inc.

Matthew B Smittle

Robert T Golla

Jama Ismail Barreh

Paul Joseph Jordan

Yuan C Chou

Xiang Shan Li

Jared C Smolens

Manish K Shah

Christopher Hans Olson

Jeffrey S Brooks

Mark Luttrell

Thomas M Wicki

Gideon N Levinsky

Nathan Francis Sheeley

Deepak Panwar

Muhammad Tauseef Rab

Mark Greenberg

Munsefar Khaleque

A memory circuit may include both an array circuit and multiple register circuits, where the power to retrieve data from one of the register circuits may be less than the power to retrieve data from the array circuit. The array circuit may store multiple data words, and the multiple register circuits may be configured to store a subset of the multiple data words. During a first cycle, a read command and an address may be received. In response to a determination that the address corresponds to a given data word included in the subset of the multiple data words, the array circuit may be de-activated in a second cycle subsequent to the first cycle and an output signal may be generated by selecting data retrieved from a particular register circuit of the multiple register circuits in which the given data word may be stored.

Memory circuit with power registers

A queue circuit that manages access to a memory circuit in a computer system includes multiple sets of entries for storing access requests. The entries in one set of entries are assigned to corresponding sources that generate access requests to the memory circuit. The entries in the other set of entries are floating entries that can be used to store requests from any of the sources. Upon receiving a request from a particular source, the queue circuit checks the entry assigned to the particular source and, if the entry is unoccupied, the queue circuit stores the request in the entry. If, however, the entry assigned to the particular source is occupied, the queue circuit stores the request in one of the floating entries.

Queue circuit for controlling access to a memory circuit

A cache memory circuit capable of dealing with multiple conflicting requests to a given cache line is disclosed. In response to receiving an acquire request for the given cache line from a particular lower-level cache memory circuit, the cache memory circuit sends probe requests regarding the given cache line to other lower-level cache memory circuits. In situations where a different lower-level cache memory circuit is simultaneously trying to evict the given cache line at the particular lower-level cache memory circuit is trying to obtain a copy of the cache line, the cache memory circuit performs a series of operations to service both requests and ensure that the particular lower-level cache memory circuit receives a copy of the given cache line that includes any changes in the evicted copy of the given cache line.

Managing multiple cache memory circuit operations

An instruction storage circuit within a processor that includes an instruction memory and a memory control circuit. The instruction memory is configured to store instructions of a program for the processor. The memory control circuit is configured to receive a particular instruction from the instruction memory, detect a data integrity error in the particular instruction, and generate and store a corrected version of the particular instruction in an error storage circuit within the instruction memory. A flush of an execution pipeline may be performed in response to the error. In response to a refetch of the particular instruction after the pipeline flush, the instruction storage circuit may be configured to cause the particular instruction to be provided from the error storage circuit to the execution pipeline to permit forward progress of the processor.

Instruction error handling

The present disclosure is directed to a mechanism for forcing a processor to enter a debug mode. In one embodiment, a processor includes a logic circuit configured to receive a halt request. In response to receiving the halt request while the processor is not in a quiescent state, the logic circuit forces the processor into the quiescent state after a threshold amount of time has elapsed. Processor operation is then halted, and the processor thus becomes accessible for a debugger to perform debug operations.

Forced debug mode entry

Techniques are disclosed relating to using non-debug path circuitry to perform debug commands. In some embodiments, an apparatus includes a processor core that includes path circuitry configured to access data for instructions executed by the processor core and storage elements which the path circuitry is configured to access via one or more ports. In some embodiments, the apparatus includes debug circuitry configured to receive external debug inputs and send abstract commands to the processor core based on the external debug inputs. In some embodiments, the apparatus includes control circuitry in the processor core configured to, in response to an abstract command to access one or more of the storage elements: generate signaling to access the one or more storage elements using the path circuitry, access read data from the one or more storage elements based on the signaling, and transmit the accessed read data to the debug circuitry.

Debug command execution using existing datapath circuitry

Techniques are disclosed relating to the handling of exceptions generated by illegal instructions in a processor. In an embodiment, a processor may be configured to fetch instructions defined according to an instruction set architecture (ISA). The ISA may include a set of uncompressed instructions and a set of compressed instructions. The processor may further be configured to, upon detecting a given one of the set of compressed instructions, cause a copy of the given compressed instruction to be saved and convert the given compressed instruction to a corresponding given uncompressed instruction. The processor may also be configured to detect that the given uncompressed instruction is illegal and was converted from the given compressed instruction, and based at least in part on these, cause an illegal instruction exception to be generated using the copy of the given compressed instruction.

Illegal instruction exception handling

Techniques are disclosed relating to cache debug using control registers based on debug commands. In some embodiments, an apparatus includes a processor core, debug circuitry, and control circuitry. In some embodiments, the debug circuitry is configured to receive external debug inputs and send abstract commands to the processor core based on the external debug inputs. In some embodiments, the control circuitry is configured to, in response to an abstract command to read data from the cache: write cache address information to a first control register, assert a trigger signal to cause a read of the data from the cache to a second control register, based on the cache address information in the first control register, and send data from the second control register to the debug circuitry. In various embodiments, this may facilitate hardware cache debug using debug circuitry that also controls software debugging.

Cache diagnostic techniques

An apparatus includes an execution unit, an instruction queue, and a control circuit. The control circuit may be configured to activate a plurality of processor threads. Each of the plurality of processor threads may include a respective plurality of instructions. The instruction queue may be configured to issue at least one instruction included in the plurality of processor threads to the execution unit at a first rate. The control circuit may also be configured to track, for a particular processor thread, a period of time from activating the particular processor thread. The instruction queue may be further configured to limit issue of a next instruction for at least one other processor thread to a second rate, based on a comparison of the period of time to a threshold amount of time. The second rate may be lower than the first rate.

Hardware mechanism to mitigate stalling of a processor core

An apparatus includes a buffer configured to store a plurality of instructions previously fetched from a memory, wherein each instruction of the plurality of instructions may be included in a respective thread of a plurality of threads. The apparatus also includes control circuitry configured to select a given thread of the plurality of threads dependent upon a number of instructions in the buffer that are included in the given thread. The control circuitry is also configured to fetch a respective instruction corresponding to the given thread from the memory, and to store the respective instruction in the buffer.

Optimizing thread selection at fetch, select, and commit stages of processor core pipeline

Systems and methods for efficient out-of-order dynamic deallocation of entries within a shared storage resource in a processor. A processor comprises a unified pick queue that includes an array configured to dynamically allocate any entry of a plurality of entries for a decoded and renamed instruction. This instruction may correspond to any available active threads supported by the processor. The processor includes circuitry configured to determine whether an instruction corresponding to an allocated entry of the plurality of entries is dependent on a speculative instruction and whether the instruction has a fixed instruction execution latency. In response to determining the instruction is not dependent on a speculative instruction, the instruction has a fixed instruction execution latency, and said latency has transpired, the circuitry may deallocate the instruction from the allocated entry.

Optimal deallocation of instructions from a unified pick queue

Systems and methods for identification of dependent instructions on speculative load operations in a processor. A processor allocates entries of a unified pick queue for decoded and renamed instructions. Each entry of a corresponding dependency matrix is configured to store a dependency bit for each other instruction in the pick queue. The processor speculates that loads will hit in the data cache, hit in the TLB and not have a read after write (RAW) hazard. For each unresolved load, the pick queue tracks dependent instructions via dependency vectors based upon the dependency matrix. If a load speculation is found to be incorrect, dependent instructions in the pick queue are reset to allow for subsequent picking, and dependent instructions in flight are canceled. On completion of a load miss, dependent operations are re-issued. On resolution of a TLB miss or RAW hazard, the original load is replayed and dependent operations are issued again from the pick queue.

Dependency matrix for the determination of load dependencies

Techniques are disclosed relating to integrated circuits that include hardware support for divide and/or square root operations. In one embodiment, an integrated circuit is disclosed that includes a division unit that, in turn, includes a normalization circuit and a plurality of divide engines. The normalization circuit is configured to normalize a set of operands. Each divide engine is configured to operate on a respective normalized set of operands received from the normalization circuit. In some embodiments, the integrated circuit includes a scheduler unit configured to select instructions for issuance to a plurality of execution units including the division unit. The scheduler unit is further configured to maintain a counter indicative of a number of instructions currently being operated on by the division unit, and to determine, based on the counter whether to schedule subsequent instructions for issuance to the division unit.

Division unit with normalization circuit and plural divide engines for receiving instructions when divide engine availability is indicated

Systems and methods for efficient picking of instructions for out-of-order issue and execution in a processor. In one embodiment, a processor comprises a unified pick queue that is dynamically allocated. Each entry is configured to store age and dependency information relative to other decoded instructions. Also, each entry stores a picked field, which when asserted indicates the decoded instruction has already been picked for out-of-order issue and execution. When asserted, a trigger field indicates a result of a corresponding decoded instruction will be available a predetermined number of clock cycles afterward. A younger instruction dependent on a result of an older instruction is ready to be picked before the result of the older instruction is available. In this case, the older instruction has asserted picked and trigger fields.

Unified high-frequency out-of-order pick queue with support for triggering early issue of speculative instructions

Various techniques for mitigating dependencies between groups of instructions are disclosed. In one embodiment, such dependencies include 'evil twin' conditions, in which a first floating-point instruction has as a destination a first portion of a logical floating-point register (e.g., a single-precision write), and in which a second, subsequent floating-point instruction has as a source the first portion and a second portion of the same logical floating-point register (e.g., a double-precision read). The disclosed techniques may be applicable in a multithreaded processor implementing register renaming. In one embodiment, a processor may enter an operating mode in which detection of evil twin 'producers' (e.g., single-precision writes) causes the instruction sequence to be modified to break potential dependencies. Modification of the instruction sequence may continue until one or more exit criteria are reached (e.g., committing a predetermined number of single-precision writes). This operating mode may be employed on a per-thread basis.

Growing community of inventors

Allen, TX, United States of America

Matthew B Smittle