Abstract: A method and apparatus handles concurrent address translation cache misses and hits under those misses while maintaining command order based upon virtual channel. Commands are stored in a command processing unit that maintains ordering of the commands. A command buffer index is assigned to each address being sent from the command processing unit to an address translation unit. When an address translation cache miss occurs, a memory fetch request is sent. The CBI is passed back to the command processing unit with a signal to indicate that the fetch request has completed. The command processing unit uses the CBI to locate the command and address to be reissued to the address translation unit.

Abstract: In a first aspect, a method for maintaining control structure coherency is provided. The method includes the steps of (1) writing a pointer to a control structure in a hardware update list while one or more portions of the control structure are accessed by hardware during a hardware update operation; and (2) delaying a software access to one or more portions of the control structure during a software update operation while the pointer to the control structure is on the hardware update list. Numerous other aspects are provided.

Abstract: Method and apparatus for prefetching cache with requested data are described. A processor initiates a read access to main memory for data which is not in the main memory. After the requested data is brought into the main memory, but before the read access is reinitiated, the requested data is prefetched from main memory into the cache subsystem of the processor which will later reinitiate the read access.

Abstract: Method and apparatus for prefetching cache with requested data are described. A processor initiates a read access to main memory for data which is not in the main memory. After the requested data is brought into the main memory, but before the read access is reinitiated, the requested data is prefetched from main memory into the cache subsystem of the processor which will later reinitiate the read access.

Abstract: A memory cache system is used in a multiprocessor environment. The first processor accesses data using a first level 1 cache, and the second processor accesses data using a second level 1 cache. A storage control circuit is positioned between the first and second level 1 caches and a level 2 cache and main memory. The level 2 cache maintains copies of data in main storage and further maintains an indication of those level 1 caches having copies of data and whether those copies have been modified. When a processor accesses data that is not resident in the connected level 1 cache, a request is delivered to the level 2 cache for this data. The level 2 cache then determines whether it can return a copy of the data to the level 1 cache or must access the data from main memory.

Abstract: A method and apparatus for handling commands and data associated therewith includes a data buffer and a command directory. The command directory receives and stores a command from at least one command source, and freely allocates an unused portion of the data buffer to the command. The data buffer stores the data associated with the command in the allocated portion of the data buffer. Based on status information also stored by the command directory with respect to each command, routing logic in the command directory, corresponding to each command sink, identifies which commands stored in the command buffer to route to the command sink, and routes the identified commands to the command sink. The routing logic also determines a priority of the identified commands and routes the identified commands in order of priority. The command directory also uses the status information to track the processing of commands.

Abstract: A hardware data string operation controller is provided which (1) performs variable length main store string operation; (2) executes at least a subset of both left to right and right to left instructions, having variable length multibyte operands; and (3) performs multicycle storage to storage operations on variable length multibyte operand data, all under the control of a single control word. The controller comprises (a) means for dynamically determining (and if necessary, adjusting) the maximum number of operand related data string bytes that can be processed (by the controller) during each machine cycle (referred to as"data mode" calculation/alteration); (b) means for performing partial machine "holdoffs" (i.e.