Background
Some systems that employ the use of PCI and PCI-X require high availability or non-stop operation. For example, many customers require computer systems that experience downtimes of just a few minutes a year, or less. Clearly, manufacturers must focus on equipment reliability, and also provide a method of identifying and repairing equipment failures quickly. An important feature in supporting these goals is the Hot Plug/Hot Swap solutions that provide three important capabilities:
a method of replacing failed expansion cards without turning the system off keeping the O/S and other services running during the repair shutting down and restarting software associated with the failed device
Prior to the widespread acceptance of PCI many proprietary Hot Plug solutions were available to support this type of removal and replacement of expansion cards. However the original PCI implementation was not designed to support hot removal and insertion of cards, but a standardized solution for supporting this capability in PCI was needed. Consequently, two major approaches to hot replacement of PCI expansion devices have been developed. These approaches are:
In both solutions, control logic is implemented to isolate the card logic from the PCI bus via electronic switches. In conjunction with isolation logic, power, reset, and clock are controlled to ensure an orderly power down and power up of cards when they are removed and replaced. Also, status and power LEDs provide indications to the user that it is safe to remove or install the card.
The need to extend hot plug support to PCI Express cards is clear. Designers of PCI Express have incorporated Hot removal and replacement of cards as a "native" feature. The specification defines configuration registers, Hot Plug Messages, and procedures to support Hot Plug solutions.
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