International Business Machines Corporation

Arm Limited

Mark Andrew Brittain

Warren Edward Maule

Jeffrey A Stuecheli

Eric Eugene Retter

John Steven Dodson

Kevin Charles Gower

Stephen J Powell

Edgar Rolando Cordero

Sanjeev Ghai

Gary Alan Morrison

Timothy Jay Dell

Benjiman L Goodman

Scott Barnett Swaney

Luiz Carlos Alves

James Stephen Fields, Jr

Karthick Rajamani

Robert Brett Tremaine

Kenneth Douglas Klapproth

Michael Andrew Campbell

John Thomas Hollaway, Jr

Joseph J Palumbo

Benjamin Lee Goodman

Vu T Le

An apparatus and method are provided for controlling access to a memory device. The apparatus has a pending access requests storage that is used to store access requests waiting to be issued to the memory device, and memory access control circuitry is then used to issue to the memory device access requests selected from the pending access requests storage. Access requests are received at an interface of the apparatus from at least one requesting device, and access request evaluation circuitry within the apparatus is arranged to apply criteria to determine, for a current access request, whether to accept that current access request or reject that current access request. The criteria applied takes account of at least one access timing characteristic of the memory device. The access request evaluation circuitry is responsive to determining that the current access request is to be accepted, to cause that current access request to be stored in the pending access requests storage. However, if instead the access request is rejected, it is prevented from being added to the pending access requests storage at that time, and instead a rejection indication is issued to the requesting device that issued that current access request. This provides a mechanism for significantly improving the performance of the memory device by providing more selectivity as to what access requests are accepted into the pending access requests storage.

Apparatus and method for controlling access to a memory device

Techniques for handling queuing of memory accesses prevent passing excessive requests that implicate a region of memory subject to a high latency memory operation, such as a memory refresh operation, memory scrubbing or an internal bus calibration event, to a re-order queue of a memory controller. The memory controller includes a queue for storing pending memory access requests, a re-order queue for receiving the requests, and a control logic implementing a queue controller that determines if there is a collision between a received request and an ongoing high-latency memory operation. If there is a collision, then transfer of the request to the re-order queue may be rejected outright, or a count of existing queued operations that collide with the high latency operation may be used to determine if queuing the new request will exceed a threshold number of such operations.

Memory queue handling techniques for reducing impact of high-latency memory operations

A method for controlling memory refresh operations in dynamic random access memories. The method includes determining a count of deferred memory refresh operations for a first memory rank. Responsive to the count approaching a high priority threshold, issuing an early high priority refresh notification for the first memory rank, which indicates the pre-determined time for performing a high priority memory refresh operation at the first memory rank. Responsive to the early high priority refresh notification, the behavior of a read reorder queue is dynamically modified to give priority scheduling to at least one read command targeting the first memory rank, and one or more of the at least one read command is executed on the first memory rank according to the priority scheduling. Priority scheduling removes these commands from the re-order queue before the refresh operation is initiated at the first memory rank.

Memory reorder queue biasing preceding high latency operations

A memory system and data processing system for controlling memory refresh operations in dynamic random access memories. The memory controller comprises logic that: tracks a time remaining before a scheduled time for performing a high priority, high latency operation a first memory rank of the memory system; responsive to the time remaining reaching a pre-established early notification time before the schedule time for performing the high priority, high latency operation, biases the re-order queue containing memory access operations targeting the plurality of ranks to prioritize scheduling of any first memory access operations that target the first memory rank. The logic further: schedules the first memory access operations to the first memory rank for early completion relative to other memory access operations in the re-order queue that target other memory ranks; and performs the high priority, high latency operation at the first memory rank at the scheduled time.

A method for performing refresh operations on a rank of memory devices is disclosed. After the completion of a memory operation, a determination is made whether or not a refresh backlog count value is less than a predetermined value and the rank of memory devices is being powered down. If the refresh backlog count value is less than the predetermined value and the rank of memory devices is being powered down, an Idle Count threshold value is set to a maximum value such that a refresh operation will be performed after a maximum delay time. If the refresh backlog count value is not less than the predetermined value or the rank of memory devices is not in a powered down state, the Idle Count threshold value is set based on the slope of an Idle Delay Function such that a refresh operation will be performed accordingly.

Method for scheduling memory refresh operations including power states

Apparatus for scheduling memory refresh operations including power states

A method and system for enabling directed temperature/power management at the DIMM-level and/or DRAM-level utilizing intelligent scheduling of memory access operations received at the memory controller. Hot spots within the memory subsystem, caused by operating the DIMMs/DRAMs above predetermined/preset threshold power/temperature values for operating a DIMM and/or a DRAM, are avoided/controlled by logic within the memory controller. The memory controller logic throttles the number/frequency at which commands (read/write operations) are issued to the specific DIMM/DRAM based on stored parameter values and tracking of outstanding operations issued to the memory subsystem devices.

Power management via DIMM read operation limiter

A memory subsystem completes multiple read operations in parallel, utilizing the functionality of buffered memory modules in a daisy chain topology. A variable read latency is provided with each read command to enable memory modules to run independently in the memory subsystem. Busy periods of the memory device architecture are hidden by allowing data buses on multiple memory modules attached to the same data channel to run in parallel rather than in series and by issuing reads earlier than required to enable the memory devices to return from a busy state earlier. During scheduling of reads, the earliest received read whose target memory module is not busy is immediately issued at a next command cycle. The memory controller provides a delay parameter with each issued read. The number of cycles of delay is calculated to allow maximum utilization of the memory modules' data bus bandwidth without causing collisions on the memory channel.

Streaming reads for early processing in a cascaded memory subsystem with buffered memory devices

A memory system is provided that manages thermal conditions at a memory device level transparent to a memory controller. The memory systems comprises a memory hub device integrated in a memory module, a set of memory devices coupled to the memory hub device, and a first set of thermal sensors integrated in the set of memory devices. A thermal management control unit integrated in the memory hub device monitors a temperature of the set of memory devices sensed by the first set of thermal sensors. The memory hub device reduces a memory access rate to the set of memory devices in response to a predetermined thermal threshold being exceeded thereby reducing power used by the set of memory devices which in turn decreases the temperature of the set of memory devices.

System to enable a memory hub device to manage thermal conditions at a memory device level transparent to a memory controller

A memory system is provided that provides memory system power reduction without reducing overall memory system performance. The memory system comprises a memory hub device integrated in a memory module. The memory hub device comprises a command queue that receives a memory access command from an memory controller via a memory channel at a first operating frequency. The memory system also comprises a memory hub controller integrated in the memory hub device. The memory hub controller reads the memory access command from the command queue at a second operating frequency. By receiving the memory access command at the first operating frequency and reading the memory access command at the second operating frequency an asynchronous boundary is implemented. Using the asynchronous boundary, the memory channel operates at a maximum designed operating bandwidth while the second operating frequency is independently decreased to reduce power being consumed by the set of memory devices.

System to provide memory system power reduction without reducing overall memory system performance

A memory system is provided that increases the overall bandwidth of a memory channel by operating the memory channel at a independent frequency. The memory system comprises a memory hub device integrated in a memory module. The memory hub device comprises a command queue that receives a memory access command from an external memory controller via a memory channel at a first operating frequency. The memory system also comprises a memory hub controller integrated in the memory hub device. The memory hub controller reads the memory access command from the command queue at a second operating frequency. By receiving the memory access command at the first operating frequency and reading the memory access command at the second operating frequency an asynchronous boundary is implemented. Using the asynchronous boundary, the memory channel operates at a maximum designed operating bandwidth, which is independent of the second operating frequency.

System to increase the overall bandwidth of a memory channel by allowing the memory channel to operate at a frequency independent from a memory device frequency

A memory system is provided that reduces latency by running a memory channel fully asynchronous from a memory device frequency. The memory system comprises a memory hub device integrated in a memory module. The memory hub device comprises a command queue that receives a memory access command from an external memory controller via a memory channel at a first operating frequency. The memory system also comprises a memory hub controller integrated in the memory hub device. The memory hub controller reads the memory access command from the command queue at a second operating frequency. By receiving the memory access command at the first operating frequency and reading the memory access command at the second operating frequency an asynchronous boundary is implemented. The first operating frequency is a maximum designed operating frequency of the memory channel and the first operating frequency is independent of the second operating frequency.

System to reduce latency by running a memory channel frequency fully asynchronous from a memory device frequency

A memory system is provided that implements an asynchronous boundary in a memory module. The memory system comprises a memory hub device integrated in a memory module. The memory system also comprises a set of memory devices coupled to the memory hub device. The memory hub device comprises a command queue that receives a memory access command from an external memory controller via a memory channel at a first operating frequency. The memory system further comprises a memory hub controller integrated in the memory hub device. The memory hub controller reads the memory access command from the command queue at a second operating frequency. By receiving the memory access command at the first operating frequency and reading the memory access command at the second operating frequency an asynchronous boundary is implemented within the memory hub device of the memory module.

System to support a full asynchronous interface within a memory hub device

A method and system is presented for correcting a data error in a primary Dynamic Random Access Memory (DRAM) in a Dual In-line Memory Module (DIMM). Each DRAM has a left half (for storing bits) and a right half (for storing bits). A determination is made as to whether the data error was in the left or right half of the primary DRAM. The half of the primary DRAM in which the error occurred is removed from service. All subsequent reads and writes for data originally stored in the primary DRAM's defective half are made to a half of a spare DRAM in the DIMM, while the DRAM's non-defective half continues to be used for subsequently storing data.

Double DRAM bit steering for multiple error corrections

A system, method, and memory controller are provided that alters a memory command stream to a hardware memory. Data is written to the hardware memory and, after the data is stored in the memory, error correction code is received from the memory. Bit errors are identified based upon the error correction code that was received. The memory command stream is then altered based upon the number of bit errors that were identified. In one embodiment, altering the memory command stream includes adjusting a memory refresh rate, while in another embodiment, altering the memory command stream includes adjusting a memory usage delay.

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Pflugerville, TX, United States of America

Mark Andrew Brittain