Information

Universal Serial Bus Interface
MPC8308 PowerQUICC II Pro Processor Reference Manual, Rev. 1
Freescale Semiconductor 13-63
13.5.6.2 Endpoint Capabilities/Characteristics
The second and third DWords of a queue head specify static information about the endpoint. This
information does not change over the lifetime of the endpoint. There are three types of information in this
region:
• Endpoint characteristics. These are the USB endpoint characteristics, which include addressing,
maximum packet size, and endpoint speed.
• Endpoint capabilities. These are adjustable parameters of the endpoint. They affect how the
endpoint data stream is managed by the host controller.
• Split transaction characteristics. This data structure manages full- and low-speed data streams for
bulk, control, and interrupt with split transactions to USB 2.0 Hub transaction translator.
Additional fields exist for addressing the hub and scheduling the protocol transactions (for
periodic).
The host controller must not modify the bits in this region.
Table 13-58 and Table 13-59 describe the endpoint characteristics.
2–1 Typ Indicates to the hardware whether the item referenced by the link pointer 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.
00 iTD (isochronous transfer descriptor)
01 QH (queue head)
10 siTD (split transaction isochronous transfer descriptor)
11 FSTN (frame span traversal node)
0TTerminate.
1 Last QH (pointer is invalid).
0 Pointer is valid.
If the queue head is in the context of the periodic list, a one bit in this field indicates to the host controller that
this is the end of the periodic list. This bit is ignored by the host controller when the queue head is in the
asynchronous schedule. Software must ensure that queue heads reachable by the host controller always
have valid horizontal link pointers.
Table 13-58. Endpoint Characteristics: Queue Head DWord 1
Bits Name Description
31–28 RL Nak count reload. This field contains a value, which is used by the host controller to reload the Nak
Counter field.
27 C Control endpoint flag. If the QH[EPS] field indicates the endpoint is not a high-speed device, and the
endpoint is a control endpoint, then software must set this bit to a one. Otherwise, it should always
set this bit to a zero.
26–16 Maximum
Packet Length
This directly corresponds to the maximum packet size of the associated endpoint
(wMaxPacketSize). The maximum value this field may contain is 0x400 (1024).
15 H Head of reclamation list flag. This bit is set by system software to mark a queue head as being the
head of the reclamation list.
Table 13-57. Queue Head DWord 0 (continued)
Bits Name Description