COHERENCY CHECKING OF INVALIDATE TRANSACTIONS CAUSED BY SNOOP FILTER EVICTION IN AN INTEGRATED CIRCUIT

摘要

An interconnect has coherency control circuitry for performing coherency control operations and a snoop filter for identifying which devices coupled to the interconnect have cached data from a given address. When an address is looked up in the snoop filter and misses, and there is no spare snoop filter entry available, then the snoop filter selects a victim entry corresponding to a victim address, and issues an invalidate transaction for invalidating locally cached copies of the data identified by the victim. The coherency control circuitry for performing coherency checking operations for data access transactions is reused for performing coherency control operations for the invalidate transaction issued by the snoop filter. This greatly reduces the circuitry complexity of the snoop filter.

主权项

1. An interconnect for connecting devices in an integrated circuit, the interconnect comprising:
coherency control circuitry capable of performing coherency control operations for transactions received by the interconnect from the devices, and determining transactions to be serviced by the devices based on the coherency control operations; and a snoop filter capable of identifying which devices have cached data for a target address of a transaction received by the interconnect, the snoop filter comprising at least one snoop filter entry for identifying which devices have cached data for a corresponding memory address; wherein in response to a transaction specifying a target address other than an address having a corresponding snoop filter entry in the snoop filter, the snoop filter is capable of allocating a new snoop filter entry for the target address; when one or more snoop filter entries which can be allocated for the target address are already allocated to another address, then the snoop filter is capable of selecting a victim snoop filter entry corresponding to a victim address, and issuing an invalidate transaction for invalidating the cached data for the victim address at one or more of the devices; and the coherency control circuitry is capable of performing the coherency control operations for the invalidate transaction issued by the snoop filter, to determine when the invalidate transaction can be serviced.