Browse Prior Art Database

Address Compares in Unaligned Storage

IP.com Disclosure Number: IPCOM000112337D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 59K

Publishing Venue

IBM

Related People

Thatcher, L: AUTHOR

Abstract

A method for making address comparisons in unaligned storage is disclosed. A comparison is made between 2 storage accesses unaligned across storage boundaries to see if either touch.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 53% of the total text.

Address Compares in Unaligned Storage

Fig. 1  The 3 Cases of Unaligned Comparisons

                      Doubleword

                       Ev Od

   Quadword Boundary  |--+-|--+-|--+-|

 Case I      Data 0          XX XX         Aligned

             Data 1          XX XX

 Case II     Data 0          XX XX         Unaligned

             Data 1       XX XX

 Case III    Data 0          XX XX         Unaligned

             Data 1             XX XX

      A method for making address comparisons in unaligned storage is
disclosed.  A comparison is made between 2 storage accesses unaligned
across storage boundaries to see if either touch.

      In high performance RISC processors store operations to cache
are often postponed and placed into queues called
Pending-Store-Queues (PSQ's).  Then when a load operation occurs it
is checked against the PSQ.  If the cache follows traditional storage
boundaries this is a simple task of comparing 2 addresses aligned to
the same boundary.  If the cache can make unaligned accesses this
becomes a much more difficult task.

      This invention is implemented in a high performance RISC
processor capable of accessing a quadword on any doubleword boundary.
This provides a high floating point performance in being able to
load/store 2 doubleword registers in a cycle on any doubleword...