SPRUIU1C July 2020 – February 2024 DRA821U , DRA821U-Q1
PCIe has multiple power management protocols. Some of them are invoked by the hardware, such as Active State Power Management (ASPM), while others are activated at higher levels via software.
The PCIe core supports D0, D1 and D3-Hot power states.
Link power states L0, L0s, L1, L1s are supported.
L0s entry and exit is managed by the PCIe core if ASPM L0s is enabled.
L1 entry and exit is also managed by the PCIe core if ASPM L1 is enabled. Software can force the exit from L1 by writing to the PCIE_USER_PMCMD[0] CLIENT_REQ_EXIT_L1 bit in the PCIe subsystem. Entry into L1 can also be blocked by setting the PCIE_USER_PMCMD[0] CLIENT_REQ_EXIT_L1 bit.
L1s support requires that the CLKREQ pin be connected to the remote peer. L1s power state is entered when the link is in L1 and CLKREQ pin is de-asserted. Software can force the exit from L1s by writing to either the PCIE_USER_PMCMD[0] CLIENT_REQ_EXIT_L1 or PCIE_USER_PMCMD[1] CLIENT_REQ_EXIT_L1_SUBSTATE bits in the PCIe subsystem.