SPRUIM2H May 2020 – October 2023 AM2431 , AM2432 , AM2434 , AM6411 , AM6412 , AM6421 , AM6422 , AM6441 , AM6442
The power management for PCIe subsystem with CBA interface is primarily accomplished through the clock stop protocol. Any time the clock stop protocol is initiated, the PCIe subsystem will acknowledge after making sure that there are no outstanding transactions. If there are any pending transactions in the subsystem, then the clock stop acknowledgement procedure cannot be completed. Therefore, it is necessary that the system software first suspend activity on the serial link as well as on the CBA interface. To do so, it is expected that the devices communicating with the device on which clock stop procedure is to be performed agree to stop transactions targeted to the device in question. Similarly, it is required that the outgoing transactions also be stopped to successfully complete the clock stop sequence. The PCIe subsystem will guarantee that in the event there are pending transactions that are still in process of draining will prevent the clock-stop acknowledgement to be issued to CBA subsystem power management logic.
The PCIe subsystem does not have ability to terminate the clock stop state. Therefore, any wakeup sequence can only be initiated through other means such as software driven timers or software detected events occurring outside of PCIe subsystem.