Data processing apparatus and method for managing snoop operations

A method of managing snoop operations in a data processing apparatus, the data processing apparatus comprising a plurality of processing units for performing data processing operations requiring access to data in shared memory, at least two of said processing units having a cache associated therewith for storing a subset of said data for access by that processing unit, the method comprising the steps of:

• employing a snoop-based cache coherency protocol to ensure data accessed by each processing unit is up-to-date;
• on issuance of an access request by one of said processing units, determining whether a snoop process is required having regard to the snoop-based cache coherency protocol;
• defining within snoop control storage a plurality of snoop schemes, each snoop scheme defining a series of snoop phases to be performed to implement the snoop process, and each snoop phase requiring a snoop operation to be performed on either a single cache or multiple caches;
• and
• when said snoop process is required, referencing the snoop control storage to identify, having regard to one or more properties of the access request, the snoop scheme to be employed to perform said snoop process.

A data processing apparatus comprising:

• a plurality of processing means for performing data processing operations requiring access to data in shared memory means;
• at least two of said processing means having a cache means associated therewith for storing a subset of said data for access by that processing means;
• cache coherency means for employing a snoop-based cache coherency protocol to ensure data accessed by each processing means is up-to-date, on issuance of an access request by one of said processing means, the cache coherency means for determining whether a snoop process is required having regard to the snoop-based cache coherency protocol;
• snoop control storage means for defining a plurality of snoop schemes, each snoop scheme defining a series of snoop phases to be performed to implement the snoop process, and each snoop phase requiring a snoop operation to be performed on either a single cache or multiple caches;
• and
• a snoop means, responsive to the cache coherency means determining that said snoop process is required, for referencing the snoop control storage means to identify, having regard to one or more properties of the access request, the snoop scheme to be employed to perform said snoop process.