Universal Serial Bus InterfaceMCF5253 Reference Manual, Rev. 1Freescale Semiconductor 24-95IN or an OUT). Refer to the EHCI Specification for a complete list of additional conditions thatmust be met in general for the host controller to issue a bus transaction. Note that the host controllermust not execute a Start-split transaction while executing in Recovery Path mode. Refer to theEHCI Specification for special handling when in Recovery Path mode.• Stop traversing the recovery path when it encounters an FSTN that is a Restore indicator. The hostcontroller unconditionally uses the saved value of the Save-Place FSTN's Normal Path LinkPointer when returning to the normal path traversal. The host controller must clear the context ofexecuting a Recovery Path when it restores schedule traversal to the Save-Place FSTN's NormalPath Link Pointer.If the host controller determines that there is not enough time left in the micro-frame to completeprocessing of the periodic schedule, it abandons traversal of the recovery path, and clears thecontext of executing a recovery path. The result is that at the start of the next consecutivemicro-frame, the host controller starts traversal at the frame list.An example traversal of a periodic schedule that includes FSTNs is illustrated in Figure 24-55.Figure 24-55. Example Host Controller Traversal of Recovery Path via FSTNsIn frame N (micro-frames 0-7), for this example, the host controller traverses all of the schedule datastructures utilizing the Normal Path Link Pointers in any FSTNs it encounters. This is because the hostcontroller has not yet encountered a Save-Place FSTN so it is not executing in Recovery Path mode. Whenit encounters the Restore FSTN, (Restore-N), during micro-frames 0 and 1, it uses Restore-N. Normal PathLink Pointer to traverse to the next data structure (that is, normal schedule traversal). This is because thehost controller must use a Restore FSTN's Normal Path Link Pointer when not executing in aRecovery-Path mode. The nodes traversed during frame N include: {82.0, 82.1, 8 2.2, 82.3, 42, 20, Restore-N,1 0...}.In frame N+1 (micro-frames 0 and 1), when the host controller encounters Save-Path FSTN (Save-N), itobserves that Save-N.Back Path Link Pointer.T-bit is zero (definition of a Save-Path indicator). The hostcontroller saves the value of Save-N. Normal Path Link Pointer and follows Save-N.Back Path Link21• • •8 78 68 58 4Normal Traversalfor Frame N+1Micro-Frames 0, 1N+1 B-PtrN-Ptr43N428 18 04140B-PtrN-Ptr2010N+3N+4N+5N–1N–2Normal Traversalfor Frame NT-Int = 1Save = NT-Int = 0Restore = NCauses ‘Restore’to Normal PathTraversalFrame NumbersRecovery PathTraversal82.383.0 83.1 83.282.0 82.1 82.2
