Oracle International Corporation

Oracle America, Inc.

Tarik Ono

Mark R Greenstreet

Suwen Yang

A source-synchronization interface circuit includes: a sender synchronous-to-asynchronous protocol converter that receives sender data and a sender clock and that has regenerative gain to resolve metastability during phase synchronization of the sender clock and a receiver clock; an asynchronous FIFO buffer with multiple stages that conveys phase information and data from the sender synchronous-to-asynchronous protocol converter to a receiver synchronous-to-asynchronous protocol converter; and a receiver synchronous-to-asynchronous protocol converter that receives the receiver clock and that has regenerative gain to resolve metastability during the phase synchronization. Moreover, the source-synchronization interface circuit includes control logic that initializes the source-synchronization interface circuit by operating the stages in the asynchronous FIFO buffer in a slow mode having a cycle time less than a data-transfer period for a predetermined number of clock cycles, and subsequently operating the stages in a normal mode having a cycle time that is less than that for the slow mode.

Deskew FIFO buffer with simplified initialization

A clock deskew circuit for transferring data from a first clock domain to a second clock domain. This circuit includes a data path, which has: a transmitter latch controlled by a transmitter clock in a first clock domain; a receiver latch controlled by a receiver clock in a second clock domain; and an intermediate latch coupled between the transmitter latch and the receiver latch. The transmitter clock and the receiver clock have an unknown phase offset. The circuit additionally includes a control circuit coupled between the transmitter clock and the receiver clock, and generates a control clock for the immediate latch based on the transmitter clock and the receiver clock. The control circuit selects between a first operation mode and a second operation mode for the data path circuit based at least on the phase relationship of the control clock with respect to the transmitter clock and the receiver clock.

Flip-flop-based clock deskew circuit

The disclosed embodiments provide a system that filters pre-fetch requests to reduce pre-fetching overhead. During operation, the system executes an instruction that involves a memory reference that is directed to a cache line in a cache. Upon determining that the memory reference will miss in the cache, the system determines whether the instruction frequently leads to cache misses. If so, the system issues a pre-fetch request for one or more additional cache lines. Otherwise, no pre-fetch request is sent. Filtering pre-fetch requests based on instructions' likelihood to miss reduces pre-fetching overhead while preserving the performance benefits of pre-fetching.

Filtering pre-fetch requests to reduce pre-fetching overhead

The disclosed embodiments provide a system that uses speculative cache requests to reduce cache miss delays for a cache in a multi-level memory hierarchy. During operation, the system receives a memory reference which is directed to a cache line in the cache. Next, while determining whether the cache line is available in the cache, the system determines whether the memory reference is likely to miss in the cache, and if so, simultaneously sends a speculative request for the cache line to a lower level of the multi-level memory hierarchy.

Using speculative cache requests to reduce cache miss delays

The disclosed embodiments provide a synchronization circuit that supports multiple parallel reads and writes. This synchronization circuit includes multiple coupled data storage locations that synchronize data and control signals between two time domains and control logic that facilitates simultaneously accessing a variable number of such data storage locations in the same clock cycle. During operation, the synchronization circuit receives a request to simultaneously access (e.g., read and/or write) two or more synchronized data storage locations. In response to the request, the control logic in the synchronization circuit determines whether the present state of the synchronization circuit can accommodate the request, and if so, simultaneously accesses two or more synchronized data storage locations.

Synchronization circuit that facilitates multiple parallel reads and writes

Embodiments of a synchronization circuit are described. This synchronization circuit includes multiple selectively coupled synchronization stages which are configurable to synchronize data and control signals between a first time domain and a second time domain, where the synchronization can be performed based on asynchronous or synchronous events associated with either the first time domain or the second time domain. Additionally, the synchronization circuit includes control logic, coupled to the synchronization stages, which is configured to adapt a number of synchronization stages used to synchronize the data and the control signals based on an estimate of a probability of metastability persisting to an output of the synchronization circuit during the synchronization.

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Cupertino, CA, United States of America

Tarik Ono