L1 Exit Triggers

The following events trigger an L1 exit:

  • Electrical idle exit detection.
  • New requests at the AXI interface.
  • Assertion of side-band signal CLIENT_REQ_EXIT_L1.
  • The root port initiates the retraining request using the link control register).

ASPM Exit

Any L1 exit triggers an L1 exit process and there is no handshake required from the client.

PCI-PM Exit

Any L1 exit triggers change the link power state to L0. However, an additional root port to endpoint handshake is required for normal operation after reaching L0.

For a root port initiated PM L1 exit:

  1. Root port initiates a configuration write to change the endpoint function's power state to D0.
  2. This configuration write triggers an L1 exit on the link.
  3. The endpoint device also exits from L1 and responds with CPL.
  4. Normal data transfer can happen on the PCIe link.

For an endpoint initiated PM L1 exit:

  1. The endpoint initiates a PM_PME message to the root port to request a power state change.
  2. The message triggers an L1 exit on the link.
  3. After receiving this message, the root port initiates a configuration write to change the endpoint function's power state to D0.
  4. The endpoint device responds with CPL.
  5. Normal data transfer can happen on the PCIe link.