Abstract: A method, an apparatus, and a computer program are provided for controlling a transmission enable (TX_ENA) signal. In Extreme Data Rate (XDR™) Dynamic Random Access Memories (DRAMs) or XDRAMS, there is a requirement that a TX_ENA signal remain logic high for a few cycles before data transmission, and, when TX_ENA transitions to logic low, TX_ENA remain logic low for a few cycles. However, maintaining this timing can be difficult with back-to-back writes. Therefore, additional logic is employed within XDRAM memory controllers to insure that TX_ENA does not violate system requirements by allowing TX_ENA to remain logic high between successive writes or when the system is devoid of commands.

Abstract: A method and apparatus for managing write-to-read turnarounds in an early read after write memory system are presented. Memory controller logic identifies a write operation's bank set, allows a different bank set read operation to issue prior to the write operation's completion, and allows a same bank set read operation to issue once the write operation completes. The memory controller includes operation counter logic, operation selection logic, operation acceptance logic, command formatting logic, and memory interface logic. The operation counter logic receives new-operation-related signals from the operation acceptance logic and, in turn, provides signals to the operation selection logic and the operation acceptance logic as to when to issue a read operation that corresponds to either an even DRAM bank or an odd DRAM bank.

Abstract: A method, an apparatus, and a computer program are provided to reuse functional data buffers. With Extreme Data Rate (XDR™) Dynamic Random Access Memory (DRAM), test patterns are employed to dynamically calibrate data with the clock. To perform this task, data buffers are employed to store data and commands for the calibration patterns. However, there are different procedures and requirements for transmission and reception calibrations. Hence, to reduce the amount of hardware needed to perform transmission and reception calibrations, the data buffers employ additional front end circuitry to reuse the buffers for both tasks.

Abstract: A structure of sequencers, a method, and a computer program are provided for performing initial and periodic calibrations in an XDR™ memory system. A memory controller that performs these calibrations is divided into identical, independent halves, with each half containing a Current/Impedance Calibration (i/z Cal) sequencer and six Bank sequencers. The i/z Cal sequencer contains three pathways that perform the XIO current and termination calibrations, and the XDR™ DRAM current and termination impedance calibrations. Each Bank sequencer contains normal read and write operation pathways that are reused to accomplish receive setup, receive hold, transmit setup, transmit hold, XIO receive, and XIO transmit timing calibrations. Initial and periodic calibrations are necessary to ensure the precise transfer of data between the XIOs and the XDR™ DRAMs.

Abstract: Embodiments of the present invention provide methods, systems and apparatus for performing memory maintenance and calibration operations. To perform calibration operations, calibration data may first be written to memory, and subsequently read back. The calibration operations may then be performed in response to detecting discrepancies between the data written and data read back from memory. To prevent the calibration data from being altered during memory maintenance operations, embodiments of the invention provide for the skipping of sections containing calibration data during the memory maintenance operations. Therefore, the calibration data is preserved, allowing for appropriate calibration operations to be performed.

Abstract: Embodiments of the present invention optimize data bandwidth across an asynchronous buffer in a system with a variable clock domain. A move signal may be asserted to transfer data associated with a command into the asynchronous buffer. After the data has been moved into the buffer, an acknowledge signal may indicate that the transfer is complete. A launch signal may transfer the data in the asynchronous buffer to memory. Embodiments of the present invention allow the processing of a next command to begin at the earliest possible time while data associated with a previous command is being transferred into and out of the buffer, thereby increasing throughput and improving performance.

Abstract: The present invention generally relates to memory controllers operating in a system containing a variable system clock. The memory controller may exchange data with a processor operating at a variable processor clock frequency. However the memory controller may perform memory accesses at a constant memory clock frequency. Asynchronous buffers may be provided to transfer data across the variable and constant clock domains. To prevent read buffer overflow while switching to a lower processor clock frequency, the memory controller may quiesce the memory sequencers and pace read data from the sequencers at a slower rate. To prevent write data under runs, the memory controller's data flow logic may perform handshaking to ensure that write data is completely received in the buffer before performing a write access.

Abstract: A method and apparatus are provided for scaling an input bandwidth for bandwidth allocation technology. An original bandwidth count value of an input flow is received. A bandwidth scaler constant is provided and used for scaling the received original bandwidth count value to provide a scaled bandwidth value between zero and one. The scaled bandwidth value is stored and used for calculating a transmit probability for the input flow.

Abstract: A memory controller capable of handling precharge-to-precharge restrictions is disclosed. Upon commencement of a write operation, the location of the corresponding write precharge command is tracked from a timing standpoint. A determination is then made as to whether or not a subsequent read precharge command will collide with any pending write precharge command. In a determination that a subsequent read precharge command will collide with any pending write precharge command, the issuance of this read precharge command is delayed in order to avoid any collision; also, a specific time interval between this read precharge command and subsequent read precharge commands is maintained.

Abstract: A memory controller capable of locating an open command cycle for the purpose of issuing a precharge packet to extreme data rate (XDR) dynamic random access memory (DRAM) devices is disclosed. In response to a receipt of two request packets concurrently, a determination is made as to whether one of the request packets includes a non-precharge command and the other one of the request packets includes a precharge command. If one of the request packets includes a non-precharge command and the other one of the request packets includes a precharge command, the request packet having a non-precharge command proceeds. In addition, the precharge command is deferred and its dynamic offset is adjusted accordingly.

Abstract: A method and system for using constraints to simplify a memory controller are presented. A memory controller design tool retrieves parameter ranges supported by a memory controller, and identifies troublesome parameter value combinations. The memory controller design tool suggests to 1) add logic to the memory controller to resolve the conflict, 2) incorporate a constraint that reduces/eliminates command collisions, data conflicts, and/or the need to check particular timing parameters, or 3) a combination of both. The memory controller design tool may work in conjunction with a memory controller designer to define and use the constraints.

Abstract: A method and apparatus to avoid collisions between row activate and column read or column write commands is presented. A memory controller includes control logic, activate allowed logic, and last column counter logic. The control logic sends particular values to the activate allowed logic and the last column counter logic at the beginning of a read or write operation, such as a new command load value, a read count value, and a write count value. In turn, the control logic receives an activate allowed signal from the activate allowed logic, which indicates the times at which a new activate command may be issued. As a result, the memory controller allows an activate command to commence on “even” command cycles or anytime after the last outstanding column command has been issued.

Abstract: A method and apparatus for managing write-to-read turnarounds in an early read after write memory system are presented. Memory controller logic identifies a write operation's bank set, allows a different bank set read operation to issue prior to the write operation's completion, and allows a same bank set read operation to issue once the write operation completes. The memory controller includes operation counter logic, operation selection logic, operation acceptance logic, command formatting logic, and memory interface logic. The operation counter logic receives new-operation-related signals from the operation acceptance logic and, in turn, provides signals to the operation selection logic and the operation acceptance logic as to when to issue a read operation that corresponds to either an even DRAM bank or an odd DRAM bank.

Abstract: In a first aspect, a first method is provided for storing a command. The first method includes the steps of (1) receiving a new command referencing an address; (2) determining whether the new command is dependent on at least one previously-received command referencing the address stored in a queue of pending commands; (3) identifying the most-recently received command of the at least one previously-received command; and (4) associating the new command with the most-recently received command of the at least one previously-received command. Numerous other aspects are provided.

Abstract: A method, an apparatus, and a computer program are provided to reuse functional data buffers. With Extreme Data Rate (XDR™) Dynamic Random Access Memory (DRAM), test patterns are employed to dynamically calibrate data with the clock. To perform this task, data buffers are employed to store data and commands for the calibration patterns. However, there are different procedures and requirements for transmission and reception calibrations. Hence, to reduce the amount of hardware needed to perform transmission and reception calibrations, the data buffers employ additional front end circuitry to reuse the buffers for both tasks.

Abstract: A method, an apparatus, and a computer program are provided to account for data stored in Dynamic Random Access Memory (DRAM) write buffers. There is difficulty in tracking the data stored in DRAM write buffers. To alleviate the difficulty, a cache line list is employed. The cache line list is maintained in a memory controller, which is updated with data movement. This list allows for ease of maintenance of data without loss of consistency.

Abstract: A method, an apparatus, and a computer program are provided to control refreshes in Extreme Data Rate (XDR™) memory systems. XDR™ memory systems employ calibrations to ensure the precise transmission of data. During calibrations, memory refreshes can occur; however, these refreshes can interfere with calibration streams. Therefore, to alleviate collisions and interferences, refreshes are deferred to periods where no calibrations are taking place. The number of deferred refreshes is also tracked such that the overall loss of refreshes is prevented.

Abstract: A structure of sequencers, a method, and a computer program are provided for performing initial and periodic calibrations in an XDR™ memory system. A memory controller that performs these calibrations is divided into identical, independent halves, with each half containing a Current/Impedance Calibration (i/z Cal) sequencer and six Bank sequencers. The i/z Cal sequencer contains three pathways that perform the XIO current and termination calibrations, and the XDR™ DRAM current and termination impedance calibrations. Each Bank sequencer contains normal read and write operation pathways that are reused to accomplish receive setup, receive hold, transmit setup, transmit hold, XIO receive, and XIO transmit timing calibrations. Initial and periodic calibrations are necessary to ensure the precise transfer of data between the XIOs and the XDR™ DRAMs.

Abstract: A method, an apparatus, and a computer program are provided for controlling a transmission enable (TX_ENA) signal. In Extreme Data Rate (XDR™) Dynamic Random Access Memories (DRAMs) or XDRAMS, there is a requirement that a TX_ENA signal remain logic high for a few cycles before data transmission, and, when TX_ENA transitions to logic low, TX_ENA remain logic low for a few cycles. However, maintaining this timing can be difficult with back-to-back writes. Therefore, additional logic is employed within XDRAM memory controllers to insure that TX_ENA does not violate system requirements by allowing TX_ENA to remain logic high between successive writes or when the system is devoid of commands.