Exiting L1 Substate

Either side can initiate a transition out of the L1 substate. The remote side initiates an L1 PM substate exit by asserting its CLKREQ# output. This assertion turns on the core clock and asserts the PCIe Controller's CLKREQ_IN_N input, causing its L1 PM substate to change to L1.0 and enabling the transition of the LTSSM from L1 into recovery. The client can also initiate the L1 exit.

The following events trigger an L1 substate exit:

  • Remote device initiated exit triggers:
    • Assert CLKREQ#.
    • Detect an electrical idle exit (only during entry into L1.1 or L1.2 substates before PHY_RX_ELEC_IDLE_DET_EN is deasserted).
  • Locally initiated exit triggers:
    • New requests at the AXI interface.
    • New register access requests.
    • Assertion of sideband signals CLIENT_REQ_EXIT_L1_SUBSTATE or CLIENT_REQ_EXIT_L1.

The L1 substate exit triggers change the link from L1.1 or L1.2 state to L1.0 and then to L0.