Abstract: An efficient system and method for managing reads and writes on a bi-directional bus to optimize bus performance while avoiding bus contention and avoiding read/write starvation. In particular by intelligently managing reads and writes on a bi-directional bus, bus latency can be reduced while still ensuring no bus contention or read/write starvation. This is accomplished by utilizing bus streaming control logic, separate queues for reads and writes, and a simple 2 to 1 mux.

Abstract: A system and method is disclosed to track a large number of open pages in a computer memory system. The computer system contains one or more processors each including a memory controller containing a page table, the page table organized into a plurality of rows with each row able to store an address of an open memory page. A RIMM module containing RDRAM devices is coupled to each processor, each RDRAM containing a plurality of memory banks. The page table increases system memory performance by tracking a large number of open memory pages. Associated with the page table is a bank active table that indicates the memory banks in each RDRAM device having open memory pages. The page table enqueues accesses to the RIMM module in a precharge queue resulting from a page miss caused by the address of an open memory page occupying the same row of the page table as the address of the system memory access resulting in the page miss.

Abstract: A computer system has a memory controller that includes read buffers coupled to a plurality of memory channels. The memory controller advantageously eliminates the inter-channel skew caused by memory modules being located at different distances from the memory controller. The memory controller preferably includes a channel interface and synchronization logic circuit for each memory channel. This circuit includes read and write buffers and load and unload pointers for the read buffer. Unload pointer logic generates the unload pointer and load pointer logic generates the load pointer. The pointers preferably are free-running pointers that increment in accordance with two different clock signals. The load pointer increments in accordance with a clock generated by the memory controller but that has been routed out to and back from the memory modules.

Abstract: A computer system has a memory controller that includes read buffers coupled to a plurality of memory channels. The memory controller advantageously eliminates the inter-channel skew caused by memory modules being located at different distances from the memory controller. The memory controller preferably includes a channel interface and synchronization logic circuit for each memory channel. This circuit includes read and write buffers and load and unload pointers for the read buffer. Unload pointer logic generates the unload pointer and load pointer logic generates the load pointer. The pointers preferably are free-running pointers that increment in accordance with two different clock signals. The load pointer increments in accordance with a clock generated by the memory controller but that has been routed out to and back from the memory modules. The unload pointer increments in accordance with a clock generated by the computer system itself.

Abstract: A computer system includes a memory controller interfacing the processor to a memory system. The memory controller supports a memory system with a plurality of memory devices, with multiple memory banks in each memory device. The memory controller supports simultaneous memory accesses to different memory banks. Memory bank conflicts are avoided by examining each transaction before it is loaded in the memory transaction queue. On a first clock cycle, the new pending memory request is transferred from a pending request queue to a memory mapper. On the subsequent clock cycle, the memory mapper formats the pending memory request into separate signals identifying the DEVICE, BANK, ROW and COLUMN to be accessed by the pending transaction. In the next clock cycle, the DEVICE and BANK signals are compared with every entry in the memory transaction queue to determine if a bank conflict exists. If so, the new memory request is rejected and recycled to the pending request queue.

Abstract: A system and method is disclosed to increase computer memory system performance by reducing lost clock cycles caused by bus turnarounds. The computer system contains one or more processors each including a memory controller containing a page table, the page table organized into a plurality of rows with each row able to store an address of an open memory page. The memory controller also contains a precharge queue, a Row-address-select (“RAS”) queue, a Column-address-select (“CAS”) Read queue, and a CAS Write queue. The CAS Read queue and CAS Write queue outputs are connected to a 2-to-1 multiplexer. The 2-to-1 multiplexer streams groups of read requests and groups of write requests to main memory resulting in fewer lost clock cycles caused by bus turnarounds. The memory controller places system memory read requests into the CAS Read queue and system memory write requests into the CAS Write queue.

Abstract: A computer system contains a processor that includes a software programmable memory mapper. The memory mapper maps an address generated by the processor into a device address for accessing physical main memory. The processor also includes a cache controller that maps the processor address into a cache address. The cache address places a block of data from main memory into a memory cache using an index subfield. The physical main memory contains RDRAM devices, each of the RDRAM devices containing a number of memory banks that store rows and columns of data. The memory mapper maps processor addresses to device addresses to increases memory system performance. The mapping minimizes memory access conflicts between the memory banks. Conflicts between memory banks are reduced by placing a number of bits corresponding to the bank subfield above the most significant boundary bit of the index subfield.

Abstract: A command queueing apparatus for directing address and command information amongst the various interfaces, or consumers, on a multi-CPU node in a computer system. The apparatus includes a core queue containing core queue entries, each core queue entry corresponding to a pending system bus operation. Each core queue entry includes one or more consumer information fields specific to each consumer. Also included is a plurality of virtual queues, each virtual queue corresponding to a consumer, each virtual queue having a virtual queue entry. A virtual queue entry for a consumer is a subset of the fields of a core queue entry, the subset of fields including the consumer information fields for the consumer corresponding to the virtual queue.

Abstract: A method and apparatus in a computer system for updating Duplicate Tag cache status information. The invention operates in a computer system having one or more processor modules coupled to a system bus operating in accordance with a SNOOPING bus protocol. Processor commands and addresses for modification of an entry of the processor's Duplicate Tag status information is provided by the processor to its address interface to the system bus. System bus command and address information is received and stored in a interface pipeline of the address interface. A determination is made as to whether the system bus commands and addresses in the interface pipeline are valid. If there are no valid system bus commands and addresses in the interface pipeline, the Duplicate Tag status information is updated without determining if the processor commands and addresses conflict with the system bus commands and addresses.

Abstract: In the operation of high-speed computers, it is frequently advantageous to employ a high speed cache memory within each CPU of a multiple CPU computer system. A standard, slower memory configuration remains in use for the large, common main memory, but those portions of main memory which are expected to be used heavily are copied into the cache memory. Thus, on many memory references, the faster cache memory is exploited, while only infrequent references to the slower main memory are necessary. This configuration generally speeds the overall operation of the computer system; however, memory integrity problems arise by maintaining two separate copies of selected portions of main memory. Accordingly, the memory access unit of the CPU uses error correction code (ECC) hardware to ensure the integrity of the data delivered between the cache and main memory. The prevent the ECC hardware from slowing the overall operation of the CPU, the error correction is performed underneath a write back operation.