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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors—USB 2.0 Host Controller
Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
Developer’s Manual
August 2006
440
Order Number: 306262-004US
Any time the host controller begins a new traversal of the Asynchronous Schedule, a
Start Event is assumed, see
“Asynchronous Schedule Traversal: Start Event” on
. Every time a Start-Event occurs, the Nak Count reload procedure is enabled.
9.14.9.1
Nak Count Reload Control
When the host controller reaches the Execute Transaction state for a queue head
(meaning that it has an active operational state), it checks to determine whether the
NakCnt field should be reloaded from RL (see
Section 9.14.10.3, “Execute Transaction”
). If the answer is yes, then RL is copied into NakCnt. After the reload or if
the reload is not active, the host controller evaluates whether to execute the
transaction.
The host controller must reload nak counters (NakCnt see
) in queue heads during the first pass through the
reclamation list after an asynchronous schedule Start Event (see
Schedule Traversal: Start Event” on page 438
for the definition of the Start Event). The
Asynchronous Schedule should have at most one queue head marked as the head (see
illustrates an example state machine that satisfies
the operational requirements of the host controller detecting the first pass through the
Asynchronous Schedule. This state machine is maintained internal to the host
controller and is only used to gate reloading of the nak counter during the queue head
traversal state: Execute Transaction (
). The host controller does
not perform the nak counter reload operation if the RL field (see
Head Structure Layout” on page 404
9.14.9.1.1
Wait for List Head
This is the initial state. The state machine enters this state from Wait for Start Event
when a start event as defined in
“Asynchronous Schedule Traversal: Start Event” on
occurs. The purpose of this state is to wait for the first observation of the
head of the Asynchronous Schedule. This occurs when the host controller fetches a
queue head whose H-bit is set to a one.
Figure 64.
Example HC State Machine for Controlling Nak Counter Reloads
4507-01
Do Reload
Wait for
Start Event
Wait for
List Head
Start Event
QH.H==1
QH.H==1