Separate Reference Clock with Independent SSC (SRIS)

The current PCI - SIG “PCI Express* External Cabling Specification” (www.pcisig.com) defines the reference clock as part of the signals delivered through the cable. Inclusion of the reference clock in the cable requires an expensive shielding solution to meet EMI requirements.

The need for an inexpensive PCIe* cabling solution for PCIe* SSDs requires a cabling form factor that supports non-common clock mode with spread spectrum enabled, such that the reference clock does not need to be part of the signals delivered through the cable. This clock mode requires the components on both sides of a link to tolerate a much higher ppm tolerance of ~5600 ppm compared to the PCIe* Base Specification defined as 600 ppm.

Soft straps are needed as a method to configure the port statically to operate in this mode. This mode is only enabled if the SSD connector is present on the motherboard, where the SSD connector does not include the reference clock. No change is being made to PCIe* add-in card form factors and solutions.

ASPM L0s is not supported in this form factor. The L1 exit latency advertised to software would be increased to 10 us. The root port does not support Lower SKP Ordered Set generation and reception feature defined in SRIS ECN.