NXP Semiconductors QorIQ LS1012A Reference Manual

• Remote-wakeup enabled device asserts resume signaling. In similar kind to USB 2.0hubs, when in host mode the host controller responds to explicit device resumesignaling and wake up the system (if necessary).• Port connect and disconnect and over-current events. Sensitivity to these events canbe turned on or off by using the port control bits in the PORTSC register.Selective suspend is a feature supported by the PORTSC register. It is used to placespecific ports into a suspend mode. This feature is used as a functional component forimplementing the appropriate power management policy implemented in a particularoperating system. When system software intends to suspend the bus, it should suspendthe enabled port, then shut off the controller by setting the USBCMD[RS] to a zero.When a wake event occurs the system will resume operation and system software mustset the RS bit to a one and resume the suspended port.32.6.4.1 Port suspend/resumeSystem software places the USB into suspend mode by writing a one into the appropriatePORTSC Suspend bit.Software must only set the Suspend bit when the port is in the enabled state (Port Enabledbit is a one).The host controller may evaluate the Suspend bit immediately or wait until a microframeor frame boundary occurs. If evaluated immediately, the port is not suspended until thecurrent transaction (if one is executing) completes. Therefore, there may be severalmicroframes of activity on the port until the host controller evaluates the Suspend bit.The host controller must evaluate the Suspend bit at least every frame boundary.System software can initiate a resume on the suspended port by writing a one toPORTSC[FPR]. Software should not attempt to resume a port unless the port reports thatit is in the suspended state. If system software sets PORTSC[FPR] when the port is not inthe suspended state, the resulting behavior is undefined. In order to assure proper USBdevice operation, software must wait for at least 10 milliseconds after a port indicates thatit is suspended (Suspend bit is a one) before initiating a port resume throughPORTSC[FPR]. When PORTSC[FPR] is set, the host controller sends resume signalingdown the port. System software times the duration of the resume (nominally 20milliseconds) then clears PORTSC[FPR]. When the host controller receives the write totransition PORTSC[FPR] to zero, it completes the resume sequence as defined in theUSB specification, and clears both PORTSC[FPR] and PORTSC[SUSP]. Software-initiated port resumes do not affect the port change detect bit (USBSTS[PCI]) nor do theycause an interrupt if USBINTR[PCE] (port change interrupt enable) is a one. When awake event occurs on a suspended port, the resume signaling is detected by the port andChapter 32 Universal Serial Bus Interface 2.0QorIQ LS1012A Reference Manual, Rev. 1, 01/2018NXP Semiconductors 1995