Information

Universal Serial Bus Interface
MPC8308 PowerQUICC II Pro Processor Reference Manual, Rev. 1
Freescale Semiconductor 13-49
13.5.3.1 Next Link Pointer
The first DWord of an iTD is a pointer to the next schedule data structure, as shown in Table 13-40.
13.5.3.2 iTD Transaction Status and Control List
DWords 1–8 constitute eight slots of transaction control and status. Each transaction description includes
the following:
• Status results field
• Transaction length (bytes to send for OUT transactions and bytes received for IN transactions).
• Buffer offset. The PG and Transaction n Offset fields are used with the buffer pointer list to
construct the starting buffer address for the transaction.
The host controller uses the information in each transaction description, plus the endpoint information
contained in the first three DWords of the buffer page pointer list, to execute a transaction on the USB.
2
These fields may be modified by the host controller if the I/O field indicates an OUT.
Table 13-40. Next Schedule Element Pointer
Bits Name Description
31–5 Link Pointer Correspond to memory address signals [31:5], respectively. This field points to another isochronous
transaction descriptor (iTD/siTD) or queue head (QH).
4–3 — Reserved, should be cleared. These bits are reserved and their value has no effect on operation.
Software should initialize this field to zero.
2–1 Typ Indicates to the host controller whether the item referenced is an iTD, siTD or a QH. This allows the host
controller to perform the proper type of processing on the item after it is fetched. Value encodings are:
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
1 Link Pointer field is not valid.
0 Link Pointer field is valid.