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IDT Link Operation
Notes
PES4T4 User Manual
sition to the L1 state from its link partner. Note that L1 entry requests are only made by the PES4T4
upstream port. If the link partner acknowledges the transition, the L1 state is entered. Otherwise the L0s
state is entered.
– The upstream switch port will only request entry into the L1 state when all of the downstream ports
which are not in a low power state (i.e., D3) and whose link is not down are in the L1 state.
Link Status
Associated with each port is a Port Link Up (PxLINKUPN) status output and a Port Activity (PxAC-
TIVEN) status output. These outputs are provided on I/O expander 4. See section I/O Expanders on page
6-5 for the operation of the I/O expander and the mapping of these status outputs to I/O expander pins.
The PxLINKUPN and PxACTIVEN status outputs may be used to provide a visual indication of system
state and activity or for debug. The PxLINKUPN output is asserted when the PCI Express data link layer is
up (i.e., when the LTSSM is in the L0, L0s, L1 or recovery states). When the data link layer is down, this
output is negated. The PxACTIVEN output is asserted whenever any TLP, other than a vendor defined
message, is transmitted or received on the corresponding port's link. Whenever a PxACTIVEN output is
asserted, it remains asserted for at least 200 ms. Since an I/O expander output may change no more
frequently than once every 40 ms, this translates into five I/O expander update periods.
4 - 4
February 1, 2011
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