06636906 is referenced by 37 patents.

A snapshot mechanism that includes an apparatus and method for tracking DMA read requests for cacheable data that can be altered before the data is returned to a requesting I/O device is herein disclosed. Attributes that uniquely identify the original I/O device and DMA read request are stored in a cache tag unit. A read lock is set when a request is made to obtain the requested data when it is not resident in a local cache. When the cache line containing the requested data is snooped out and the read lock is set, then the cache line is set in a snapshot state. The snapshot state assures that only the original I/O device receives the read data when it has been altered subsequent to the time the original DMA read request was made. Once the data is returned to the original I/O device, the cache line is invalidated in order to prevent another I/O device from reading the stale data. Prefetched data is marked as such and cannot be marked as snapshot data.

Title
Apparatus and method for ensuring forward progress in coherent I/O systems
Application Number
9/560553
Publication Number
6636906 (B1)
Application Date
April 28, 2000
Publication Date
October 21, 2003
Inventor
Carl H Jackson
Plano
TX, US
Joe P Cowan
Fort Collins
CO, US
John A Wickeraad
Granite Bay
CA, US
Sharon M Ebner
Mountain View
CA, US
Debendra Das Sharma
Santa Clara
CA, US
Agent
Clare T Hartnett
US
Assignee
Hewlett Packard Development Company
TX, US
IPC
G06F 13/28
View Original Source