Table of Contents
Advertisement
USB 2.0 Host Controller—Intel
Table 176.
Actions for Park Mode, Based on Endpoint Response and Residual Transfer
State (Sheet 2 of 2)
PID
PING
Notes:
1.
The host controller may continue to execute bus transactions from the current high-speed queue
head (if PM-Count is not equal to zero), if a PID mismatch is detected (e.g. expected DATA1 and
received DATA0, or visa-versa).
2.
This specification does not require that the host controller execute another bus transaction when PM-
Count is non-zero. Implementations are encouraged to make appropriate complexity and
performance trade-offs.
9.14.10.4
Write Back qTD
This state is entered from the Execute Transaction state when the Active bit is set to
a zero. The source data for the write-back is the transfer results area of the queue head
overlay area (see
controller uses the Current qTD Pointer field as the target address for the qTD. The
queue head transfer result area is written back to the transfer result area of the target
qTD. This state is also referred to as: qTD retirement. The fields that must be written
back to the source qTD include Total Bytes to Transfer, Cerr, and Status.
The duration of this state depends on when the qTD write-back has been committed.
9.14.10.5
Follow Queue Head Horizontal Pointer
The host controller must use the horizontal pointer in the queue head to the next
schedule data structure when any of the following conditions exist:
• If the Active bit is a one on exit from the Execute Transaction state, or
• When the host controller exits the Write Back qTD state, or
• If the Advance Queue state fails to advance the queue because the target qTD is
not active, or
• If the Halted bit is a one on exit from the Fetch QH state.
There is no functional requirement that the host controller wait until the current
transaction is complete before using the horizontal pointer to read the next linked data
structure. However, it must wait until the current transaction is complete before
executing the next data structure.
9.14.10.6
Buffer Pointer List Use for Data Streaming with qTDs
A qTD has an array of buffer pointers, which is used to reference the data buffer for a
transfer. This specification requires that the buffer associated with the transfer be
virtually contiguous. This means: if the buffer spans more than one physical page, it
must obey the following rules:
• The first portion of the buffer must begin at some offset in a page and extend
through the end of the page.
• The remaining buffer cannot be allocated in small chunks scattered around
memory. For each 4K chunk beyond the first page, each buffer portion matches to
August 2006
Order Number: 306262--, Revision: 004US
®
®
IXP45X and Intel
IXP46X Product Line of Network Processors
Transfer State after
Endpoint
Response
PM-Count
ACK
Not Zero
NAK
Don't care
STALL, XactErr
Don't care
Figure 50, "Queue Head Structure Layout" on page
Transaction
Bytes to
Transfer
Allowed to perform another bus
Not Zero
transaction.
Don't care
Move to next QH
Don't care
Move to next QH
®
®
Intel
IXP45X and Intel
IXP46X Product Line of Network Processors
Action
2
404). The host
Developer's Manual
449
Advertisement
Table of Contents
