International Business Machines Corporation

Melissa Ann Barnum

Lonny Lambrecht

Paul Allen Ganfield

Mark David Bellows

Tolga Ozguner

Kent Harold Haselhorst

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.

Memory controller operating in a system with a variable system clock

Separate handling of read and write operations of Read-Modify-Write Commands in an XDR&#x2122; memory system is provided. This invention allows the system to issue other commands between the reads and writes of a RMW. This insures that the dataflow time from read to write is not a penalty. A RMW buffer is used to store the read data and a write buffer is used to store the write data. A MUX is used to merge the read data and the write data, and transmit the merged data to the target DRAM via the XIO. The RMW buffer can also be used for scrubbing commands.

Separate handling of read and write of read-modify-write

A method, an apparatus, and a computer program are provided for the separate handling of read and write operations of Read-Modify-Write Commands in an XDR&#x2122; memory system. This invention allows the system to issue other commands between the reads and writes of a RMW. This insures that the dataflow time from read to write is not a penalty. A RMW buffer is used to store the read data and a write buffer is used to store the write data. A MUX is used to merge the read data and the write data, and transmit the merged data to the target DRAM via the XIO. The RMW buffer can also be used for scrubbing commands.

An arbitration structure, a method, and a computer program are provided for an arbitration scheme that can handle a plurality of memory commands in an operating system. Typically, in a memory system there are three types of memory commands: periodic, read, and write. An arbitration scheme determines the order of priority in which these commands are executed. This arbitration scheme is flexible because it contains a read/write priority module, which can be programmed to execute any order of priority combination of read and write commands. This enables an arbitration scheme for any memory system to be easily programmed for maximum efficiency.

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Kasson, MN, United States of America

Melissa Ann Barnum