Standard Hot Plug Controller Signaling Interface

Figure 17-3 on page 669 represents a more detailed view of the logic within root and switch ports, along with the signals routed between the slot and port. The importance of the standardized Hot Plug Controller is the common software interface that allows the device driver to be integrated into operating systems.

The PCI Express specification in conjunction with the Card ElectroMechanical (CEM) specification define the slot signals and the support required for Hot Plug PCI Express. Following is a list of required and optional port interface signals needed to support the Standard Usage Model:

• PWRLED# (required) — port output that controls state of Power Indicator

• ATNLED# (required) — port output controls state of Attention Indicator

• PWREN (required, if reference clock is implemented) — port output that controls main power to slot

• REFCLKEN# (required) — port output that controls delivery of reference clock to the slot

• PERST# (required) — port output that controls PERST# at slot

• PRSNT1# (required) — Grounded at the connector

• and PRSNT2# (required) — port input indicates presence of card in slot. Also pulled up on system board

• PWRFLT# (required) — port input that notifies the Hot-Plug controller of a power fault condition detected by external logic

• AUXEN#(required, if AUX power is implemented) — port output that controls switched AUX signals and AUX power to slot when MRL is opened and closed. The MRL# signal is required with AUX power is present.

• MRL# (required if MRL Sensor is implemented, otherwise it's optional) — port input from the MRL sensor

• BUTTON# (required if Attention Button is implemented, otherwise it's optional) — port input indicating operator wishes to perform a Hot-Plug operation