International Business Machines Corporation

Qualcomm Incorporated

Victor Roberts Augsburg

Thomas Andrew Sartorius

James Norris Dieffenderfer

Jeffrey Todd Bridges

Rodney Wayne Smith

Bernard Charles Drerup

Richard Gerard Hofmann

Barry Joe Wolford

Thomas Philip Speier

Michael Scott McIlvaine

Robert Douglas Clancy

Kenneth Alan Dockser

Thomas Kevin Collopy

Brian Joseph Kopec

Brian Stempel

Jaya Prakash Subramaniam Ganasan

Michael S Mcilvaine

Brian Michael Stempel

A processor includes a conditional branch instruction prediction mechanism that generates weighted branch prediction values. For weakly weighted predictions, which tend to be less accurate than strongly weighted predictions, the power associating with speculatively filling and subsequently flushing the cache is saved by halting instruction prefetching. Instruction fetching continues when the branch condition is evaluated in the pipeline and the actual next address is known. Alternatively, prefetching may continue out of a cache. To avoid displacing good cache data with instructions prefetched based on a mispredicted branch, prefetching may be halted in response to a weakly weighted prediction in the event of a cache miss.

Power efficient instruction prefetch mechanism

A Block Normal Cache Allocation (BNCA) mode is defined for a processor. In BNCA mode, cache entries may only be allocated by predetermined instructions. Normal memory access instructions (for example, as part of interrupt code) may execute and will retrieve data from main memory in the event of a cache miss; however, these instructions are not allowed to allocate entries in the cache. Only the predetermined instructions (for example, those used to establish locked cache entries) may allocate entries in the cache. When the locked entries are established, the processor exits BNCA mode, and any memory access instruction may allocate cache entries. BNCA mode may be indicated by setting a bit in a configuration register.

Cache locking without interference from normal allocations

Address translation performance within a processor is improved by identifying an address that causes a boundary crossing between different pages in memory and linking address translation information associated with both memory pages. According to one embodiment of a processor, the processor comprises circuitry configured to recognize an access to a memory region crossing a page boundary between first and second memory pages. The circuitry is also configured to link address translation information associated with the first and second memory pages. Thus, responsive to a subsequent access the same memory region, the address translation information associated with the first and second memory pages is retrievable based on a single address translation.

Address translation method and apparatus

Data from a source domain operating at a first data rate is transferred to a FIFO in another domain operating at a different data rate. The FIFO buffers data before transfer to a sink for further processing or storage. A source side counter tracks space available in the FIFO. In disclosed examples, the initial counter value corresponds to FIFO depth. The counter decrements in response to a data ready signal from the source domain, without delay. The counter increments in response to signaling from the sink domain of a read of data off the FIFO. Hence, incrementing is subject to the signaling latency between domains. The source may send one more beat of data when the counter indicates the FIFO is full. The last beat of data is continuously sent from the source until it is indicated that a FIFO position became available; effectively providing one more FIFO position.

Latency insensitive FIFO signaling protocol

A method for optimizing throughput in a microprocessor that is capable of processing multiple threads of instructions simultaneously. Instruction issue logic is provided between the input buffers and the pipeline of the microprocessor. The instruction issue logic speculatively issues instructions from a given thread based on the probability that the required operands will be available when the instruction reaches the stage in the pipeline where they are required. Issue of an instruction is blocked if the current pipeline conditions indicate that there is a significant probability that the instruction will need to stall in a shared resource to wait for operands. Once the probability that the instruction will stall is below a certain threshold, based on current pipeline conditions, the instruction is allowed to issue.

Speculative instruction issue in a simultaneously multithreaded processor

A processor having a multistage pipeline includes a TLB and a TLB controller. In response to a TLB miss signal, the TLB controller initiates a TLB reload, requesting address translation information from either a memory or a higher-level TLB, and placing that information into the TLB. The processor flushes the instruction having the missing virtual address, and refetches the instruction, resulting in re-insertion of the instruction at an initial stage of the pipeline above the TLB access point. The initiation of the TLB reload, and the flush/refetch of the instruction, are performed substantially in parallel, and without immediately stalling the pipeline. The refetched instruction is held at a point in the pipeline above the TLB access point until the TLB reload is complete, so that the refetched instruction generates a 'hit' in the TLB upon its next access.

Translation lookaside buffer manipulation

A method of managing cache partitions provides a first pointer for higher priority writes and a second pointer for lower priority writes, and uses the first pointer to delimit the lower priority writes. For example, locked writes have greater priority than unlocked writes, and a first pointer may be used for locked writes, and a second pointer may be used for unlocked writes. The first pointer is advanced responsive to making locked writes, and its advancement thus defines a locked region and an unlocked region. The second pointer is advanced responsive to making unlocked writes. The second pointer also is advanced (or retreated) as needed to prevent it from pointing to locations already traversed by the first pointer. Thus, the pointer delimits the unlocked region and allows the locked region to grow at the expense of the unlocked region.

Method and apparatus for managing cache partitioning using a dynamic boundary

In an instruction execution pipeline, the misalignment of memory access instructions is predicted. Based on the prediction, an additional micro-operation is generated in the pipeline prior to the effective address generation of the memory access instruction. The additional micro-operation accesses the memory falling across a predetermined address boundary. Predicting the misalignment and generating a micro-operation early in the pipeline ensures that sufficient pipeline control resources are available to generate and track the additional micro-operation, avoiding a pipeline flush if the resources are not available at the time of effective address generation. The misalignment prediction may employ known conditional branch prediction techniques, such as a flag, a bimodal counter, a local predictor, a global predictor, and combined predictors. A misalignment predictor may be enabled or biased by a memory access instruction flag or misaligned instruction type.

Methods and apparatus for predicting unaligned memory access

A processor includes a hierarchical Translation Lookaside Buffer (TLB) comprising a Level-1 TLB and a small, high-speed Level-0 TLB. Entries in the L0 TLB replicate entries in the L1 TLB. The processor first accesses the L0 TLB in an address translation, and access the L1 TLB if a virtual address misses in the L0 TLB. When the virtual address hits in the L1 TLB, the virtual address, physical address, and page attributes are written to the L0 TLB, replacing an existing entry if the L0 TLB is full. The entry may be locked against replacement in the L0 TLB in response to an L0 Lock (L0L) indicator in the L1 TLB entry. Similarly, in a hardware-managed L1 TLB, entries may be locked against replacement in response to an L1 Lock (L1L) indicator in the corresponding page table entry.

TLB lock indicator

A system for optimizing translation lookaside buffer entries is provided. The system includes a translation lookaside buffer configured to store a number of entries, each entry having a size attribute, each entry referencing a corresponding page, and control logic configured to modify the size attribute of an existing entry in the translation lookaside buffer if a new page is contiguous with an existing page referenced by the existing entry. The existing entry after having had its size attribute modified references a consolidated page comprising the existing page and the new page.

Method and system for optimizing translation lookaside buffer entries

A processor includes a cache memory having at least one entry managed according to a copy-back algorithm. A global modified indicator (GMI) indicates whether any copy-back entry in the cache contains modified data. On a cache miss, if the GMI indicates that no copy-back entry in the cache contains modified data, data fetched from memory are written to the selected entry without first reading the entry. In a banked cache, two or more bank-GMIs may be associated with two or more banks. In an n-way set associative cache, n set-GMIs may be associated with the n sets. Suppressing the read to determine if the copy-back cache entry contains modified data improves processor performance and reduces power consumption.

Global modified indicator to reduce power consumption on cache miss

A method of designing a system on a chip (SoC) to operate with varying latencies and frequencies. A layout of the chip is designed with specific placement of devices, including a bus controller, initiator, and target devices. The time for a signal to propagate from a source device to a destination device is determined relative to a default propagation time. A pipeline stage is then inserted into a bus path between said source device and destination device for each additional time the signal takes to propagate. Each device (i.e., initiators, targets, and bus controller) is designed with logic to control a protocol that functions with a variety of response latencies. With the additional logic, the devices do not need to be changed when pipeline stages are inserted in the various paths. Registers are utilized as the pipeline stages that are inserted within the paths.

Growing community of inventors

Cary, NC, United States of America

Victor Roberts Augsburg