Abstract: Aspects of the present disclosure relate to an apparatus comprising processing circuitry, first cache circuitry and second cache circuitry, wherein the second cache circuitry has an access latency higher than an access latency of the first cache circuitry. The second cache circuitry is responsive to receiving a request for data stored within the second cache circuitry to identify said data as pseudo-invalid data and provide said data to the first cache circuitry. The second cache circuitry is responsive to receiving an eviction indication, indicating that the first cache circuitry is to evict said data, to, responsive to determining that said data has not been modified since said data was provided to the first cache circuitry, identify said pseudo-invalid data as valid data.

Abstract: An apparatus and method for handling stash requests are described. The apparatus has a processing element with an associated storage structure that is used to store data for access by the processing element, and an interface for coupling the processing element to interconnect circuitry. Stash request handling circuitry is also provided that, in response to a stash request targeting the storage structure being received at the interface from the interconnect circuitry, causes a block of data associated with the stash request to be stored within the storage structure. The stash request identifies a given address that needs translating into a corresponding physical address in memory, and also identifies an address space key. Address translation circuitry is used to convert the given address identified by the stash request into the corresponding physical address by performing an address translation that is dependent on the address space key identified by the stash request.

Abstract: In response to determining circuitry determining that a portion of data to be sent to a recipient over an interconnect has a predetermined value, data sending circuitry performs data elision to: omit sending at least one data FLIT corresponding to the portion of data having the predetermined value; and send a data-elision-specifying FLIT specifying data-elision information indicating to the recipient that sending of the at least one data FLIT has been omitted and that the recipient can proceed assuming the portion of data has the predetermined value. The data-elision-specifying FLIT is a FLIT other than a write request FLIT for initiating a memory write transaction sequence. This helps to conserve data FLIT bandwidth for other data not having the predetermined value.

Abstract: A request node is provided comprising request circuitry to issue write requests to write data to storage circuitry. The write requests are issued to the storage circuitry via a coherency node. Status receiving circuitry receives a write status regarding write operations at the storage circuitry from the coherency node and throttle circuitry throttles a rate at which the write requests are issued to the storage circuitry in dependence on the write status. A coherency node is also provided, comprising access circuitry to receive a write request from a request node to write data to storage circuitry and to access the storage circuitry to write the data to the storage circuitry. Receive circuitry receives, from the storage circuitry, an incoming write status regarding write operations at the storage circuitry and transmit circuitry transmits an outgoing write status to the request node based on the incoming write status.

Abstract: An apparatus and method for handling stash requests are described. The apparatus has a processing element with an associated storage structure that is used to store data for access by the processing element, and an interface for coupling the processing element to interconnect circuitry. Stash request handling circuitry is also provided that, in response to a stash request targeting the storage structure being received at the interface from the interconnect circuitry, causes a block of data associated with the stash request to be stored within the storage structure. The stash request identifies a given address that needs translating into a corresponding physical address in memory, and also identifies an address space key. Address translation circuitry is used to convert the given address identified by the stash request into the corresponding physical address by performing an address translation that is dependent on the address space key identified by the stash request.

Abstract: Circuitry comprises a set of two or more data handling nodes each having respective storage circuitry to hold data; and a home node to serialise data access operations and to control coherency amongst data held by the one or more data handling nodes so that data written to a memory address is consistent with data read from that memory address in response to a subsequent access request; in which: a requesting node of the set of data handling nodes is configured to communicate a request to the home node for exclusive access to a given instance of data at a given memory address; and the home node is configured, in response to the request, to communicate information to other data handling nodes of the set of data handling nodes to control handling, by those other data handling nodes, of any further instances of the data at the given memory address which are held by those other data handling nodes.

Abstract: Apparatus and a corresponding method of operating a hub device, and a target device, in a coherent interconnect system are presented. A cache pre-population request of a set of coherency protocol transactions in the system is received from a requesting master device specifying at least one data item and the hub device responds by cause a cache pre-population trigger of the set of coherency protocol transactions specifying the at least one data item to be transmitted to a target device. This trigger can cause the target device to request that the specified at least one data item is retrieved and brought into cache. Since the target device can therefore decide whether to respond to the trigger or not, it does not receive cached data unsolicited, simplifying its configuration, whilst still allowing some data to be pre-cached.

Abstract: A data processing system (2) incorporates a first exclusive cache memory (8, 10) and a second exclusive cache memory (14). A snoop filter (18) located together with the second exclusive cache memory on one side of the communication interface (12) serves to track entries within the first exclusive cache memory. The snoop filter includes retention data storage circuitry to store retention data for controlling retention of cache entries within the second exclusive cache memory. Retention data transfer circuitry (20) serves to transfer the retention data to and from the retention data storage circuitry within the snoop filter and the second cache memory as the cache entries concerned are transferred between the second exclusive cache memory and the first exclusive cache memory.

Abstract: A data processing apparatus is provided, which includes receiving circuitry to receive a snoop request in respect of requested data on behalf of a requesting node. The snoop request includes an indication as to whether forwarding is to occur. Transmitting circuitry transmits a response to the snoop request and cache circuitry caches at least one data value. When forwarding is to occur and the at least one data value includes the requested data, the response includes the requested data and the transmitting circuitry transmits the response to the requesting node.

Abstract: A request node is provided comprising request circuitry to issue write requests to write data to storage circuitry. The write requests are issued to the storage circuitry via a coherency node. Status receiving circuitry receives a write status regarding write operations at the storage circuitry from the coherency node and throttle circuitry throttles a rate at which the write requests are issued to the storage circuitry in dependence on the write status. A coherency node is also provided, comprising access circuitry to receive a write request from a request node to write data to storage circuitry and to access the storage circuitry to write the data to the storage circuitry. Receive circuitry receives, from the storage circuitry, an incoming write status regarding write operations at the storage circuitry and transmit circuitry transmits an outgoing write status to the request node based on the incoming write status.

Abstract: An apparatus to is provided, to be used with an interconnect comprising a home node. The apparatus includes general-purpose storage circuitry and specialised storage circuitry. Transfer circuitry performs a non-forwardable transfer of a data item from the general-purpose storage circuitry to the specialised storage circuitry. Transmit circuitry transmits an offer to the home node, at a time of the non-forwardable transfer, to transfer the data item to the home node. The apparatus is inhibited from forwarding the data item from the specialised storage circuitry to the home node.

Abstract: A data processing apparatus is provided that includes a plurality of storage elements. Receiving circuitry receives a plurality of incoming data beats from cache circuitry and stores the incoming data beats in the storage elements. At least one existing data beat in the storage elements is replaced by an equal number of the incoming data beats belonging to a different cache line of the cache circuitry. The existing data beats stored in said plurality of storage elements form an incomplete cache line.

Abstract: An apparatus to is provided, to be used with an interconnect comprising a home node. The apparatus includes general-purpose storage circuitry and specialised storage circuitry. Transfer circuitry performs a non-forwardable transfer of a data item from the general-purpose storage circuitry to the specialised storage circuitry. Transmit circuitry transmits an offer to the home node, at a time of the non-forwardable transfer, to transfer the data item to the home node. The apparatus is inhibited from forwarding the data item from the specialised storage circuitry to the home node.

Abstract: Circuitry comprises a set of two or more data handling nodes each having respective storage circuitry to hold data; and a home node to serialise data access operations and to control coherency amongst data held by the one or more data handling nodes so that data written to a memory address is consistent with data read from that memory address in response to a subsequent access request; in which: a requesting node of the set of data handling nodes is configured to communicate a request to the home node for exclusive access to a given instance of data at a given memory address; and the home node is configured, in response to the request, to communicate information to other data handling nodes of the set of data handling nodes to control handling, by those other data handling nodes, of any further instances of the data at the given memory address which are held by those other data handling nodes.

Abstract: A requester issues a request specifying a target address indicating an addressed location in a memory system. A completer responds to the request. Tag error checking circuitry performs a tag error checking operation when the request issued by the requester is a tag-error-checking request specifying an address tag. The tag error checking operation comprises determining whether the address tag matches an allocation tag stored in the memory system associated with a block of one or more addresses comprising the target address specified by the tag-error-checking request. The requester and the completer communicate via a memory interface having at least one data signal path to exchange read data or write data between the requester and the completer; and at least one tag signal path, provided in parallel with the at least one data signal path, to exchange address tags or allocation tags between the requester and the completer.

Abstract: A requester issues a request specifying a target address indicating an addressed location in a memory system. A completer responds to the request. Tag error checking circuitry performs a tag error checking operation when the request issued by the requester is a tag-error-checking request specifying an address tag. The tag error checking operation comprises determining whether the address tag matches an allocation tag stored in the memory system associated with a block of one or more addresses comprising the target address specified by the tag-error-checking request. The requester and the completer communicate via a memory interface having at least one data signal path to exchange read data or write data between the requester and the completer; and at least one tag signal path, provided in parallel with the at least one data signal path, to exchange address tags or allocation tags between the requester and the completer.

Abstract: The present disclosure is concerned with improvements to cache systems that can be used to improve the performance (e.g. hit performance) and/or bandwidth within a memory hierarchy. For instance, a data processing apparatus is provided that comprises a cache. Access circuitry receives one or more requests for data and when the data is present in the cache the data is returned. Retrieval circuitry retrieves the data and stores the data in the cache, either proactively or in response to the one or more requests for the data. Control circuitry evicts the data from the cache and, in dependence on at least one condition, stores the data in the further cache. The at least one condition comprises a requirement that the data was stored into the cache proactively and that a number of the one or more requests is above a threshold value.

Abstract: Storage circuitry is provided, that is designed to form part of a memory hierarchy. The storage circuitry comprises receiver circuitry for receiving a request to obtain data from the memory hierarchy. Transfer circuitry causes the data to be stored at a selected destination in response to the request, wherein the selected destination is selected in dependence on at least one selection condition. Tracker circuitry tracks the request while the request is unresolved. If at least one selection condition is met then the destination is the storage circuitry and otherwise the destination is other storage circuitry in the memory hierarchy.

Abstract: An apparatus and method are provided for processing ownership upgrade requests in relation to cached data. The apparatus has a plurality of processing units, at least some of which have associated cache storage. A coherent interconnect couples the plurality of master units with memory, the coherent interconnect having a snoop unit used to implement a cache coherency protocol when a request received by the coherent interconnect identifies a cacheable memory address within the memory. Contention management circuitry is provided to control contended access to a memory address by two or more processing units within the plurality of processing units.

Abstract: A memory controller comprises memory access circuitry configured to initiate a data access of data stored in a memory in response to a data access hint message received from another node in data communication with the memory controller; to access data stored in the memory in response to a data access request received from another node in data communication with the memory controller and to provide the accessed data as a data access response to the data access request.