Method and apparatus for maintaining cache coherency in a computer system with a highly pipelined bus and multiple conflicting snoop requests

• US 5,875,467 A
• Filed: 04/04/1997
• Issued: 02/23/1999
• Est. Priority Date: 12/06/1995
• Status: Expired due to Fees

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Merchant, Amit A.
• Primary Examiner(s): BRAGDON, REGINALD GLENWOOD
• Application Number:
  US08/826,556
• Time in Patent Office: 690 Days
• Field of Search: 711/146, 711/140, 711/169, 711/3, 711/152, 711/167, 711/163, 711/158, 711/145, 395/726, 395/874
• US Class Current: 711/140
• CPC Class Codes: G06F 12/0831 using a bus scheme, e.g. with bus monitoring or watching means
• CPC Class Codes: G06F 12/0833 in combination with broadcast means (e.g. for invalidation or updating)

Abstract

A method of maintaining cache coherency for snoop operations includes initiating a first snoop operation in response to a snoop request while one or more previous snoop operations are pending in a queue. Furthermore, one or more subsequent snoop operations can be queued, wherein a step of determining if the one or more snoop requests are orthogonal, i.e. the processing of one request is not dependent on the outcome of a previous request, is included. The step of determining if the one or more snoop requests are orthogonal includes utilizing a block bit, a sleep bit, and a plurality of previously pending snoop request bits in a snoop queue entry to determine if the entry is orthogonal or not.

Claims

1. A method of handling multiple snoop requests in a processor comprising the steps of:

(a) initiating a first snoop operation in response to a snoop request while one or more previous snoop operations are pending;

(b) queuing one or more subsequent snoop requests; and

(c) determining which of the one or more subsequent snoop requests are orthogonal, wherein the step of determining includes utilizing a first block indication, a second block indication and a history indication associated with a particular one of said one or more subsequent snoop requests to determine if said particular one of said one or more subsequent snoop requests is orthogonal with other snoop requests that are pending.

2. The method of handling multiple snoop requests of claim 1 wherein address matching is used to block the one or more subsequent snoop requests from starting one or more subsequent snoop operations until the first snoop operation completes.

3. The method of handling multiple snoop requests of claim 1 wherein the first snoop operation has an address associated with it, and each of the one or more previous snoop operations have an address associated with it, the method further comprising the steps of:

(d) comparing the address of the first snoop operation with the addresses of the one or more previous snoop operations to see if there is a match; and

(e) blocking the one or more subsequent snoop requests from starting one or more subsequent snoop operations until the first snoop operation completes if a match is found in the step (c).