Presence Detection

When a module is plugged in and power is supplied, the physical layer will detect the presence of the device, and the root port sets SLSTS.PDS and SLSTS.PDC. If SLCTL.PDE and SLCTL.HPE are both set, the root port will also generate an interrupt.

When a module is removed (using the physical layer detection), the root port clears SLSTS.PDS and sets SLSTS.PDC. If SLCTL.PDE and SLCTL.HPE are both set, the root port will also generate an interrupt.

SMI/SCI Generation

Interrupts for power - management events are not supported on legacy operating systems. To support power - management on non - PCI Express* aware operating systems, power management events can be routed to generate SCI. To generate SCI, MPC.HPCE must be set. When set, enabled hot - plug events will cause SMSCS.HPCS to be set.

Additionally, BIOS workaround for hot - plug can be supported by setting MPC.HPME. When this bit is set, hot - plug events can cause SMI status bits in SMSCS to be set. Supported hot - plug events and their corresponding SMSCS bit are:

• Presence Detect Changed – SMSCS.HPPDM
• Link Active State Changed – SMSCS.HPLAS

When any of these bits are set, SMI# will be generated. These bits are set regardless of whether interrupts or SCI is enabled for hot - plug events. The SMI# may occur concurrently with an interrupt or SCI.