Universal Serial Bus InterfaceMCF5253 Reference Manual, Rev. 124-66 Freescale Semiconductor24.8.7.1 FTSN Normal Path PointerThe first DWord of an FSTN contains a link pointer to the next schedule object. This object can be of anyvalid periodic schedule data type.24.8.7.2 FSTN Back Path Link PointerThe second DWord of an FTSN node contains a link pointer to a queue head. If the T-bit in this pointer isa zero, then this FSTN is a Save-Place indicator. Its Typ field must be set by the software to indicate thetarget data structure is a queue head. If the T-bit in this pointer is set, then this FSTN is the Restoreindicator. When the T-bit is a one, the host controller ignores the Typ field.24.9 Host OperationsThe general operational model is for the USB modules in host mode is defined by the Enhanced HostController Interface (EHCI) Specification. The EHCI specification describes the register-level interfacefor a host controller for the USB Revision 2.0. It includes a description of the hardware/software interfaceTable 24-60. FTSN Normal Path PointerBit Name Description31–5 NPLP Normal Path Link Pointer. This field contains the address of the next data object to be processed in the periodiclist and corresponds to memory address signals [31–5], respectively.4–3 – Reserved. These bits must be written as 0s.2–1 Typ This field indicates to the host controller whether the item referenced is a iTD/siTD, a QH or an FSTN. This allowsthe host controller to perform the proper type of processing on the item after it is fetched.00 iTD (isochronous transfer descriptor)01 QH (queue head)10 siTD (split transaction isochronous transfer descriptor)11 FSTN (Frame Span Traversal Node)0 T Terminate.0 Link Pointer is valid.1 Link Pointer field is not valid.Table 24-61. FSTN Back Path Link PointerBit Name Description31–5 BPLP Back Path Link Pointer. This field contains the address of a Queue Head. This field corresponds to memoryaddress signals [31–5], respectively.4–3 – Reserved. These bits must be written as 0s.2–1 Typ The software must ensure this field is set to indicate the target data structure is a Queue Head (01). Any othervalue in this field yields undefined results.0 T Terminate.0 Link Pointer is valid (that is, the host controller may use bits [31–5] (in combination with the CTRLDSSEGMENTregister if applicable) as a valid memory address). This value also indicates that this FSTN is a Save-Placeindicator.1 Link Pointer field is not valid (that is, the host controller must not use bits [31–5] (in combination with theCTRLDSSEGMENT register if applicable) as a valid memory address). This value also indicates that this FSTNis a Restore indicator.
