International Business Machines Corporation

Thomas D Kim

John R Hattersley

Forrest A Reiley

Jeffery Y Lee

Dynamic address translation structures and procedures are capable of multiple address translations for the same processor in a single cycle. According to one approach, a plurality of directory look aside tables (DLATs) are used to provide multiple address translation. The DLATs are accessed in parallel by separate virtual address generators. To avoid the problem of generating the same address multiple times for each of the DLATs, a generated address for one DLAT may be written to all the DLATs or, alternatively, if a miss occurs in one DLAT, a search is made of the other DLATs before the address is generated. In the former case, an address written to all the DLATs may overwrite an address that will be needed for a future translation by one of the other DLATs. This is avoided in the latter case, but translations in other DLATs are interrupted when a miss occurs in one of the DLATs. This, in turn, may be avoided by employing 'shadow' DLATs which are copies of the DLATs. The shadow DLATs are searched when a miss occurs in one of the DLATs thereby avoiding any interruption of translations by the DLATs themselves. Rather than use multiple DLATs, a single interleaved DLAT may be used by multiple address generators.

Multiple virtual address translation per computer cycle

An address translation mechanism for generating real addresses, within a page. based on stride from a beginning translated address in the page. However, whenever there is a page crossing, an address must go to either the directory look aside table (DLAT) or buffer control element (BCE) to translate a virtual page-address to a real page-address. To avoid the delay this usually causes, the address translation request is sent out before the address is actually needed. This is done by predicting the next page-crossing while real addresses with the current page are being generated based on the stride value. The prediction is based on the stride value, operand size, and page mode.

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Highland Park, NJ, United States of America

Thomas D Kim