Endpoint Capabilities/Characteristics; Endpoint Characteristics: Queue Head Dword 1 - Intel IXP45X Developer's Manual

USB 2.0 Host Controller—Intel
Table 160. Queue Head DWord 0
Bit
31:5
4:3
2:1
0
9.13.6.2

Endpoint Capabilities/Characteristics

The second and third DWords of a Queue Head specifies 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 including
addressing, maximum packet size, and endpoint speed.
• Endpoint Capabilities. These are adjustable parameters of the endpoint. They effect
how the endpoint data stream is managed by the host controller.
• Split Transaction Characteristics. This data structure is used to manage full- and
low-speed data streams for bulk, control, and interrupt via split transactions to
USB 2.0 hub Transaction Translator. There are additional fields used for addressing
the hub and scheduling the protocol transactions (for periodic).
The host controller must not modify the bits in this region.
Table 161. Endpoint Characteristics: Queue Head DWord 1 (Sheet 1 of 2)
Bit
31:28
27
26:16
15
August 2006
Order Number: 306262--, Revision: 004US
® ®
IXP45X and Intel IXP46X Product Line of Network Processors
Queue Head Horizontal Link Pointer (QHLP). This field contains the address of the next data
object to be processed in the horizontal list and corresponds to memory address signals [31:5],
respectively.
(Reserved). These bits must be written as zeros.
QH/(s)iTD Select (Typ). This field 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. Value encodings are:
Value Meaning
00b iTD (isochronous transfer descriptor)
01b QH (queue head)
10b siTD (split transaction isochronous transfer descriptor)
11b FSTN (frame span traversal node)
Terminate (T).
0 = Pointer is valid.
1 = Last QH (pointer is invalid).
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.
Nak Count Reload (RL). This field contains a value, which is used by the host controller to
reload the Nak Counter field.
Control Endpoint Flag (C). 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.
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).
Head of Reclamation List Flag (H). This bit is set by System Software to mark a queue head
as being the head of the reclamation list.
Description
Description
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Intel IXP45X and Intel IXP46X Product Line of Network Processors
Developer's Manual
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