Technique for handling prefetching using trigger circuitry

Abstract

An apparatus has cache circuitry providing a cache storage to store data for access by processing circuitry, and request handling circuitry arranged to process requests, each request providing an address indication for associated data. The request handling circuitry determines with reference to the address indication whether the associated data is available in the cache circuitry. The cache circuitry forms a given level of a multi-level memory hierarchy, and the request handling circuitry is responsive to determining that the associated data is unavailable in the cache circuitry to issue an onward request to cause the associated data to be retrieved into the cache circuitry from a lower level of the multi-level memory hierarchy than the given level. Prefetch circuitry issues, as one type of request to be handled by the request handling circuitry, prefetch requests, and the request handling circuitry is arranged in response to a given prefetch request to retrieve into the cache circuitry the associated data in anticipation of that associated data being requested by the processing circuitry. In addition, trigger circuitry, responsive to a specified condition being detected in respect of the given prefetch request, issues a prefetch trigger signal for receipt by control circuitry associated with further cache circuitry at a higher level of the multi-level memory hierarchy, to cause a higher level prefetch procedure to be triggered by the control circuitry to retrieve the associated data from the cache circuitry into the further cache circuitry.