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IDT Link Operation
Notes
PES48H12G2 User Manual
L0s ASPM
L0s entry/exit operates independently for each direction of the link. On the receive side, the
PES48H12G2 upstream and downstream ports always respond to L0s entry/exit requests from the link
partner. On the transmit side, the L0s entry conditions must be met for 7us before the hardware transitions
the transmit link to the L0s state.
L0s Entry Conditions
The transmit side L0s entry conditions depend on the port's operational state. A port configured in
'Upstream Switch Port' mode initiates L0s entry when all of the conditions listed below are met:
– L0s ASPM is enabled via the port's PCIELCTL register.
– The following conditions are met for the amount of time specified in the above field:
• The receive lanes of all of the switch downstream ports in the partition which are not in a low
power state (i.e., D3) and whose link is not down are in the L0s state.
• The port has no TLPs to transmit or there are no available flow control credits to transmit a TLP.
• The port has no DLLPs pending for transmission.
A port configured in 'Downstream Switch Port' mode initiates L0s entry when all of the conditions listed
below are met:
– L0s ASPM is enabled via the port's PCIELCTL register.
– The following conditions are met for the amount of time specified in the above field:
• The receive lanes of the switch partition's upstream port are in the L0s state.
• The switch partition has no TLPs to transmit on the downstream port or there are no available
flow control credits to transmit a TLP.
• There are no DLLPs pending for transmission on the downstream port.
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 partition 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 partition 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 PES48H12G2 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 PES48H12G2 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
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April 5, 2013
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