IDT 89HPES48T12G2, User Manual, Page: 77 / 276

IDT Link Operation
PES48T12G2 User Manual 6 - 13 April 5, 2013
Notes L0s Exit Conditions
The transmit side L0s exit conditions depend on the port’s operational state. A port configured in
‘Upstream Switch Port’ mode initiates exit from L0s when any of the conditions listed below are met:
– The port has a TLP or DLLP scheduled for transmission.
– A downstream port in the switch has initiated exit from L0s.
A port configured in ‘Downstream Switch Port’ mode initiates exit from L0s when any of the conditions
listed below are met:
– The port has a TLP or DLLP scheduled for transmission.
– The upstream port in the switch has initiated exit from L0s.
L1 ASPM
L1 entry/exit is initiated by downstream link components (i.e., upstream ports) and affects both direc-
tions of the link. Upstream link components (i.e., downstream ports) accept or reject L1 entry requests from
the link partner.
L1 Entry Conditions
The PES48T12G2 downstream ports may accept or reject L1 entry requests sent by the link partner. A
port configured in ‘Downstream Switch Port’ mode accepts L1 entry requests when all of the conditions
listed below are met. Else, the L1 entry request is rejected.
– L1 ASPM is enabled via the port’s PCIELCTL register.
– The port has no TLPs pending for transmission.
– The port has no ACK or NAK DLLPs pending for transmission.
The PES48T12G2 upstream ports request entry into L1 based on the criteria defined below. The L1
entry conditions must be met for 1 ms before the upstream port transitions the link to the L1 state. If these
conditions are met and the link is in the L0 or L0s states, then the hardware will request a transition to the
L1 state from its link partner. If the link partner acknowledges the transition, then the L1 state is entered.
Otherwise, L0s entry is attempted
1
A port configured in ‘Upstream Switch Port’ mode initiates L1 entry
when all of the conditions listed below are met:
– L1 ASPM is enabled via the port’s PCIELCTL register.
– 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.
– The port has no TLPs pending for transmission.
The port’s replay-buffer is empty.
– The port has no DLLPs pending for transmission.
– The port’s receiver is idle (i.e., no TLPs or DLLPs are received) for the amount of time specified
above.
– The port has accumulated enough flow-control header and data credits to transmit the largest
possible packet of each type (i.e., posted, non-posted, or completion).
L1 Exit Conditions
The L1 exit conditions depend on the port’s operational state. A port configured in ‘Upstream Switch
Port’ mode initiates exit from L1 when any of the conditions listed below are met:
– The port has a TLP scheduled for transmission.
– A downstream port in the switch has initiated exit from L1.
The latency between the downstream port’s initiated exit from L1 and the upstream port’s initi-
ated exit from L1 must not exceed 1 µs.
A port configured in ‘Downstream Switch Port’ mode initiates exit from L1 when any of the conditions
listed below are met:
– The port has a TLP scheduled for transmission.
– The upstream port in the switch has initiated exit from L1.
The latency between the upstream port’s initiated exit from L1 and the downstream port’s initi-
ated exit from L1 must not exceed 1 µs.
1.
L0s entry is subject to the rules specified in section L0s ASPM on page 6-12.