NXP Semiconductors QorIQ LS1012A Reference Manual

NOTESoftware must ensure that no interface data structure reachableby the device controller spans a 4K-page boundary.The data structures defined in the section are (from the device controller's perspective) amix of read-only and read/writable fields. The device controller must preserve the read-only fields on all data structure writes.The USB DR module includes DCD software called the USB 2.0 Device API. The deviceAPI provides an easy to use Application Program Interface for developing device(peripheral) applications. The device API incorporates and abstracts for the applicationdeveloper all of the elements of the program interface.ENDPOINTLISTADDRUp to32 ElementsEndpoint QH 1 - OutEndpoint QH 0 - InEndpoint QH 0 - OutEndpoint Transfer DescriptorTransferBufferPointerTransferBufferTransferBufferTransferBufferTransferBufferTransfer Buffer PointerTransfer Buffer PointerTransfer Buffer PointerEndpoint Queue HeadsFigure 32-21. Endpoint queue head organization32.7.1 Endpoint queue headThe device endpoint queue head (dQH) is where all transfers are managed.The dQH is a 48-byte data structure, but must be aligned on 64-byte boundaries. Duringpriming of an endpoint, the dTD (device transfer descriptor) is copied into the overlayarea of the dQH, which starts at the nextTD pointer DWord and continues through theend of the buffer pointers DWords. After a transfer is complete, the dTD status DWord isupdated in the dTD pointed to by the currentTD pointer. While a packet is in progress,the overlay area of the dQH is used as a staging area for the dTD so that the DeviceController can access needed information with little minimal latency.The figure below shows the endpoint queue head structure.Device data structuresQorIQ LS1012A Reference Manual, Rev. 1, 01/20182064 NXP Semiconductors