Connect PCI Express Subsystems With Advanced Switching Fabrics

Maintaining Order
AS ordering and deadlock avoidance rules provide compliance with these same rules for PCI Express Base (and PCI), although the rules for AS and PCI Express Base aren’t identical. Unlike AS, PCI Express technology requires that writes bypass completions to avoid deadlocks. This rule exists in PCI Express standards to support (now obsolete) PCI bridges that don’t support delayed transactions. AS doesn’t require the capability because it guarantees forward progress for completions. Nevertheless, writes can bypass completions on the PCI Express side of an AS-to-PCI Express bridge.

However, these differences are made transparent to PCI Express devices and software by AS flow-control mechanisms and the PI-8 bridge architecture. As a result, PCI Express/PCI transactions can be transported transparently from one subsystem to another via the AS fabric while maintaining strong ordering and remaining free from deadlock.

To summarize, PCI Express Base and AS are designed to be complementary, despite the divergence between the two standards at the transaction layer. AS is a natural fit for high-end switching fabrics, and through the use of PI-8 switching devices, both standards can be intertwined. These switches ensure proper translation of routing methods, and provide system configuration, buffer-management techniques, and a transaction ordering process to bridge the different methodologies of each standard. Even all legacy PCI Express software can be maintained with the fabric-manager node running on the AS fabric.