Universal Serial Bus InterfaceMCF5253 Reference Manual, Rev. 124-114 Freescale Semiconductor24.9.12.3.6 Complete-Split for Scheduling Boundary Cases 2a, 2bBoundary cases 2a and 2b (INs only) (see Figure 24-57) require that the host controller use the transactionstate context of the previous siTD to finish the split transaction. Table 24-70 enumerates the transactionstate fields.NOTETP and T-count are used only for Host to Device (OUT) endpoints.If the software has budgeted the schedule of this data stream with a frame wrap case, then it must initializethe siTD[Back Pointer] field to reference a valid siTD and have the T bit in the siTD[Back Pointer] fieldcleared. Otherwise, the software must set the T bit in siTD[Back Pointer]. The host controller's rules forinterpreting when to use the siTD[Back Pointer] field are listed below. These rules apply only when thesiTD's Active bit is a one and the SplitXState is Do Complete Split.• When cMicroFrameBit is a 0x1 and the siTDX [Back Pointer] T-bit is zero, or• If cMicroFrameBit is a 0x2 and siTDX[S-mask[0]] is zeroWhen either of these conditions apply, then the host controller must use the transaction state from siTDX-1 .In order to access siTDX-1 , the host controller reads on-chip the siTD referenced from siTDX [BackPointer].The host controller must save the entire state from siTDX while processing siTD X-1. This is toaccommodate for case 2b processing. The host controller must not recursively walk the list of siTD[BackPointers].If siTD X-1 is active (Active bit is set and SplitXStat is Do Complete Split), then both Test A and Test B areapplied as described above. If these criteria to execute a complete-split are met, the host controller executesthe complete split and evaluates the results as described above. The transaction state (see Table 24-70) ofsiTD X-1 is appropriately advanced based on the results and written back to memory. If the resultant stateof siTDX-1 's Active bit is a one, then the host controller returns to the context of siTD X, and follows itsnext pointer to the next schedule item. No updates to siTDX are necessary.If siTD X-1 is active (Active bit is set and SplitXStat is Do Start Split), then the host controller must clearthe Active bit and set the Missed Micro-Frame status bit and the resultant status is written back to memory.If siTDX-1 's Active bit is cleared, (because it was cleared when the host controller first visited siTDX-1 viasiTD X's back pointer, it transitioned to zero as a result of a detected error, or the results of siTDX-1 'scomplete-split transaction cleared it), then the host controller returns to the context of siTDX andtransitions its SplitXState to Do Start Split. The host controller then determines whether the case 2b startsplit boundary condition exists (that is, if cMicroframeBit is 1 and siTDX [S-mask[0]] is 1). If this criterionTable 24-70. Summary siTD Split Transaction StateBuffer State Status Execution ProgressTotal Bytes To TransferP (page select)Current OffsetTP (transaction position)T-count (transaction count)All bits in the status field C-prog-mask
