ACS (Access Control Services) is used to control which devices are allowed to communicate with one another, and thus avoid improper routing of packets. It is specially appropriate with ATS. 

Core supports up to 32 Egress Vector. ACS Source Validation & ACS Translation Blocking are implemented in core for downstream ports; all other checks must be implemented in app/switching logic. Well-defined interfaces will enable selectively controlled access between PCI Express Endpoints and between Functions within a multi-function device. Some of the benefits enabled through the use of these controls include:

  • Use of ACS to prevent many forms of silent data corruption by preventing PCI Express requests from being routed to a peer Endpoint  incorrectly. As an example, if there is silent corruption of an address within a Request header within a PCI Express Switch (such as in an implementation of store-and-forward), the transaction may be routed to a downstream Endpoint or Root Port incorrectly and processed as if it were a valid transaction. This could create a number of problems which might not be detected by the associated application or service.
  • ACS can be used to preclude PCI Express Requests from routing between Functions within a multi-function device,  preventing data leakage.
  • The use of ACS to validate that the Request transactions between two downstream components is allowed. This validation can occur within the intermediate components or within the RC itself.
  • In systems using ATS, ACS can enable the direct routing of peer-to-peer Memory Requests whose addresses have been correctly Translated, while blocking or redirecting peer-to-peer Memory Requests whose addresses have not been Translated. 



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