The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Feb. 01, 2000
Filed:
May. 13, 1998
Philip Erna Milling, Austin, TX (US);
International Business Machines Corporation, Armonk, NY (US);
Abstract
The present invention provides a method and apparatus for providing memory coherency among an L1 and an L2 cache memory devices and a main memory device. In an embodiment of the invention, a memory controller generates an address snoop for locating modified copies of a data residing in the main memory. As a result of the snoop, the memory controller is notified as to whether a modified copy of the data is in the cache memory devices. If both cache memory devices have a modified copy of the data, the modified copy in the L2 cache will not be allowed to be transferred since modified copies of data in the L1 cache memory are considered to always be the most recent copies of the data. Thus, if the L1 cache memory is unable to transfer the data, The memory controller will continue to snoop the address until the L1 cache memory transfers the data. If, however, there is only one copy of the modified data and it resides in the L2 cache memory device, the copy will be allowed to be transferred to the memory controller.