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Avoidance of deadlock for some PCI host bridges

IP.com Disclosure Number: IPCOM000014056D
Original Publication Date: 2001-Feb-01
Included in the Prior Art Database: 2003-Jun-19
Document File: 4 page(s) / 72K

Publishing Venue

IBM

Abstract

On the PCI system displayed below, multiple PCI Busses are connected together via PCI Host Bridges and PCI PCI Bridge Systems. The Host Processor can communicate with any of the PCI slot’s adapters on the Primary and Secondary PCI Busses. The PCI PCI Bridge Systems have connections to three PCI Busses; the Secondary PCI Bus, and two Primary PCI Busses. This PCI PCI Bridge System configuration allows any two adapters in the system to communicate with each other without using the Host Processor Bus, thus leaving the Host Processor Complex unaffected by the communication between the two adapters. This frees the Host Processor Bus for other operations. This configuration does present a problem with a possible deadlock condition when two adapters are communicating in opposite directions through the same PCI PCI Bridge System. For example, when an adapter in slot0 on PPCI-1 is communicating with an adapter in slot2 on PPCI-2 through PCI-PCI Bridge System 1. In this article, a solution to avoid this deadlock condition will be presented. S L

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Avoidance of deadlock for some PCI host bridges

    On the PCI system displayed below, multiple PCI Busses are connected together via PCI Host Bridges and PCI - PCI Bridge Systems. The Host Processor can communicate with any of the PCI slot's adapters on the Primary and Secondary PCI Busses. The PCI - PCI Bridge Systems have connections to three PCI Busses; the Secondary PCI Bus, and two Primary PCI Busses. This PCI - PCI Bridge System configuration allows any two adapters in the system to communicate with each other without using the Host Processor Bus, thus leaving the Host Processor Complex unaffected by the communication between the two adapters. This frees the Host Processor Bus for other operations.

This configuration does present a problem with a possible deadlock condition when two adapters are communicating in opposite directions through the same PCI - PCI Bridge System. For example, when an adapter in slot0 on PPCI-1 is communicating with an adapter in slot2 on PPCI-2 through PCI-PCI Bridge System 1. In this article, a solution to avoid this deadlock condition will be presented.

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    In Figure 1, a PCI Bus system is shown containing Primary and Secondary busses, that are interconnected by PCI-PCI Bridge Systems. PPCI-1 is the first primary PCI Bus, PPCI-2 is the second primary PCI Bus, and PPCI-3 is the third primary PCI Bus. Each of these primary PCI Busses have three slots for adapters. The secondary PCI Busses are designated SPCI-1, SPCI-2, and SPCI-3 and they each have four PCI slots for adapters. The primary PCI busses each contain three PCI adapter cards in addition to the connection to their respective local and remote secondary PCI Busses via a custom PCI-PCI Bridge System. Each of the secondary PCI Busses contain four PCI adapters.

    Any of the PCI adapters on the Secondary or Primary PCI Busses can communicate to each other without use of the Host Processor Bus via the custom PCI-PCI Bridge System. When two adapters are communicating through the same PCI-PCI Bridge System, there is a possible deadlock condition when both are writing to each other. A PCI deadlock in the PCI-PCI Bridge System, would hang all the communications that needed to use that path. This deadlock can be avoided in various ways, of which one method will be presented here.

In Figure 2 below, some details of the PCI-PCI Bridge System are shown. The local and remote Primary PCI Busses and the Secondary PCI Bus are connected to PCI Host Bridges with a local bus interface on...