NXP Semiconductors QorIQ LS1012A Reference Manual

33.4.4.3.1 LHCRST behaviorThe xHCI Specification does not describe the programming model of light reset. It onlyspecifies that the Operational and Runtime Registers that are not contained in the AuxPower well are at their default values.Light reset must only be applied when USB_DCTL[Run_Stop] is equal to '0' to ensurethat there is no discrepancy between hardware and software states. If light reset is appliedduring a transfer, the behavior on the USB is undefined, and may cause a packet to beterminated abruptly.On light reset, the hardware resets all non-Aux registers to their default values whichmeans that the port state (which is contained in PORTSC) does not change, butUSB_DCTL[Run_Stop] is immediately set to '0' and all the context information aboutconnected devices is lost. It is the responsibility of software to re-initialize the controller.33.4.4.3.2 ENT requirementsIn the xHCI Specification, the rules about when the ENT (Evaluate Next TRB) flag in aTRB must be set or cleared are not very strict. However, it states that the ENT flag mustbe set to '1' in the last Normal TRB when a TD ends with an Event Data TRB.The controller requires software to follow these rules:1. Regardless of whether the endpoint is stream-capable or not, if a TD ends with anEvent Data TRB, the Normal TRB that precedes it must have ENT set to '1'. ThisNormal TRB may be separated from the Event Data TRB by a Link TRB2. In all other cases, the ENT flag must be set to '0' Failure to follow these rules resultsin undefined behavior.33.4.4.3.3 Behavior on babble errorIf a babble error is detected and the received data passes all integrity checks, the hostcontroller may write the received data (up to the expected data length) to the data buffer,and the value of the TRB transfer length field in the babble detected error transfer eventshall be consistent with the number of data bytes written to the buffer.The controller does not write the received data to the data buffer. The entire packet isdiscarded and the residual byte count is written to the TRB transfer length field.Chapter 33 Universal Serial Bus Interface 3.0QorIQ LS1012A Reference Manual, Rev. 1, 01/2018NXP Semiconductors 2291