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Method for Using In-Band Means for Establishing Endpoint Designations for a Peripheral Component Interconnect Express Generation 3 Link

IP.com Disclosure Number: IPCOM000235984D
Publication Date: 2014-Apr-01
Document File: 4 page(s) / 47K

Publishing Venue

The IP.com Prior Art Database

Abstract

A method is disclosed for establishing one or more root-endpoint designations for one or more Peripheral Component Interconnect Express (PCIe*) generation 3 (gen3) links using an in-band means.

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This is the abbreviated version, containing approximately 41% of the total text.

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Method for Using In-Band Means for Establishing Endpoint Designations for a Peripheral Component Interconnect Express Generation 3 Link

A popular standard for I/O connectivity in one or more compute servers is Peripheral Component Interconnect Express (PCIe*). When using PCIe to provide a point-to-point connection, the physical link layer initialization protocol allows the option to connect downstream-facing ports together to allow communication between root complexes. However, in certain applications, the equalization of the link circuitry is not possible at generation 3 (gen3) speeds unless each end of the link is configured to have a unique designation, with one end configured as the downstream-facing or 'root' node, and the other end configured as the upstream-facing or 'endpoint' node. When a PCIe link is used to provide connections between a compute complex that includes at least one of a processor and a memory and I/O complex that includes at least one of a switch and an adapter, the designation of link endpoints is implicit, wherein the compute complex is

the root and the I/O complex is the endpoint. However, when the PCIe link is used as a

communication channel between two compute complexes, the link endpoint

designations are not obvious.

If both compute complexes are under the same management domain, then the node assignment choice can be made by the system manager. If the compute complexes are not under the same management domain, a sideband channel on another interface could be used to establish root-endpoint assignments but at the expense of having such an additional path. Another potential solution is to have, when attempting to

establish link initialization, both ends of the link randomly choose a designation and randomly rotate through being root or endpoint until link initialization is successful.

When the two ends of a PCIe gen3 link are under separate management domains, the most desirable solution for establishing the root-endpoint designations is one that is deterministic and does not require a sideband interface.

Disclosed is a method for establishing one or more root-endpoint designations for one or more PCIe gen3 links using in-band means. The method deterministically assigns the one or more root-endpoint designations to one or more nodes of the one or more PCIe gen3 links where each node is under a separate management domain. The one or more PCIe gen3 links are capable of negotiating to a lesser generation of PCIe such as, but not limited to, a generation 1 (gen1) and generation 2 (gen2). Due to the lower link speeds of previous versions of PCIe such as gen1 and gen2, the requirement for explicit root-endpoint node designation can be easily relaxed, thus, supporting a connection configuration known as crosslink.

The method uses the above mentioned characteristics for initializing the one or more PCIe gen3 links. Initially, the method utilizes driver firmware on both sides of the one or more PCIe gen3 link...