Expansion of cross-domain addressing for PCI-express packets passing through non-transparent bridge

摘要

A PCI-Express compatible switch is provided with two or more, internal virtual buses. In one embodiment, at least one of the plural virtual buses is designated as a special bus that is limited to having no more than 16 devices on it even though the protocol allows for more. In a supplemental or alternate embodiment, at least one virtual bus is limited to having no devices on it. A non-transparent bridge is provided on at least one of the special buses for providing cross-border routing of packets from one root domain to another root domain. The number-of-devices limitation placed on the special bus reduces the number of bits needed in a corresponding Device identifying field of a destination ID Tag to 4 or less, this integer number being smaller than the prescribed 5 bits called for by the PCI-Express standard for addressing the maximum of 32 devices per bus.