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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
August 2006
Developer’s Manual
Order Number: 306262--, Revision: 004US
393
USB 2.0 Host Controller—Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
9.13.3.2
iTD Transaction Status and Control List
DWords 1 through 8 are eight slots of transaction control and status. Each transaction
description includes:
• Status results field
• Transaction length (bytes to send for OUT transactions and bytes received for IN
transactions).
• Buffer offset. The PG and Transaction X 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.
Table 144.
Next Schedule Element Pointer
Bit
Description
31:5
Link Pointer (LP). These bits 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). These bits are reserved and their value has no effect on operation. Software should
initialize this field to zero.
2:1
QH/(s)iTD Select (Typ). This field 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:
Value Meaning
00b iTD (isochronous transfer descriptor)
01b QH (queue head)
10b siTD (split transaction isochronous transfer descriptor
11b FSTN (frame span traversal node)
0
Terminate (T).
0 = Link Pointer field is valid.
1 = Link Pointer field is not valid.
Table 145.
iTD Transaction Status and Control (Sheet 1 of 2)
Bit
Description
31:28
Status. This field records the status of the transaction executed by the host controller for this slot.
This field is a bit vector with the following encoding:
31
Active. Set to one by software to enable the execution of an isochronous transaction by the Host
Controller. When the transaction associated with this descriptor is completed, the Host Controller
sets this bit to zero indicating that a transaction for this element should not be executed when it is
next encountered in the schedule.
30
Data Buffer Error. Set to a one by the Host Controller during status update to indicate that the
Host Controller is unable to keep up with the reception of incoming data (overrun) or is unable to
supply data fast enough during transmission (under run). If an overrun condition occurs, no action
is necessary.
29
Babble Detected. Set to one by the Host Controller during status update when” babble” is
detected during the transaction generated by this descriptor.
28
Transaction Error (XactErr). Set to one by the Host Controller during status update in the case
where the host did not receive a valid response from the device (Timeout, CRC, Bad PID, etc.).
This bit may only be set for isochronous IN transactions.
27:16
Transaction X Length. For an OUT, this field is the number of data bytes the host controller will
send during the transaction. The host controller is not required to update this field to reflect the
actual number of bytes transferred during the transfer. For an IN, the initial value of the endpoint
to deliver. During the status update, the host controller writes back the field is the number of bytes
the host expects the number of bytes successfully received. The value in this register is the actual
byte count (e.g. 0àzero length data, 1àone byte, 2àtwo bytes, etc.). The maximum value this field
may contain is 0xC00 (3072).