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USB 2.0 Host Controller—Intel
T-Count is always initialized to the number of start-splits for the current frame. TP is
always initialized to the first required transaction position identifier. The scheduling
boundary case (see
used to determine the initial value of TP. The initial cases are summarized in
Table 181.
Initial Conditions for OUT siTD's TP and T-count Fields
Case
1, 2a
1, 2a
After each start-split transaction is complete, the host controller updates T-Count and
TP appropriately so that the next start-split is correctly annotated.
all of the TP and T-count transitions, which must be accomplished by the host
controller.
Table 182.
Transaction Position (TP)/Transaction Count (T-Count) Transition Table
TP
ALL
BEGIN
BEGIN
MID
MID
The start-split transactions do not receive a handshake from the transaction translator,
so the host controller always advances the transfer state in the siTD after the bus
transaction is complete. To advance the transfer state the following operations take
place:
• The siTD.Total Bytes To Transfer and the siTD.Current Offset fields are adjusted to
reflect the number of bytes transferred.
• The siTD.P (page selector) bit is updated appropriately.
• The siTD.TP and siTD.T-count fields are updated appropriately as defined in
Table
These fields are then written back to the memory based siTD. The S-mask is fixed for
the life of the current budget. As mentioned above, TP and T-count are set specifically
in each siTD to reflect the data to be sent from this siTD. Therefore, regardless of the
value of S-mask, the actual number of start-split transactions depends on T-count (or
equivalently, Total Bytes to Transfer). The host controller must set the Active bit to a
zero when it detects that all of the schedule data has been sent to the bus. The
preferred method is to detect when T-Count decrements to zero as a result of a start-
split bus transaction. Equivalently, the host controller can detect when Total Bytes to
Transfer decrements to zero. Either implementation must ensure that if the initial
condition is Total Bytes to Transfer equal to zero and T-count is equal to a one, then
the host controller will issue a single start-split, with a zero-length data payload.
Software must ensure that TP, T-count and Total Bytes to Transfer are set to deliver the
appropriate number of bus transactions from each siTD. An inconsistent combination
will yield undefined behavior.
August 2006
Order Number: 306262--, Revision: 004US
®
®
IXP45X and Intel
IXP46X Product Line of Network Processors
Figure 73, "siTD Scheduling Boundary Examples" on page
T-count
TP
When the OUT data payload is less than (or equal to) 188 bytes, only one
=1
ALL
start-split is required to move the data. The one start-split must be
marked with an ALL.
When the OUT data payload is greater than 188 bytes more than one
!=1
BEGIN
start-split must be used to move the data. The initial start-split must be
marked with a BEGIN.
T-count
TP
Next
Next
0
N/A
Transition from ALL, to done.
1
END
Transition from BEGIN to END. Occurs when T-count starts at 2.
!=1
MID
Transition from BEGIN to MID. Occurs when T-count starts at greater than 2.
TP stays at MID while T-count is not equal to 1 (e.g. greater than 1). This case
!=1
MID
can occur for any of the scheduling boundary cases where the T-count starts
greater than 3.
Transition from MID to END. This case can occur for any of the scheduling
1
END
boundary cases where the T-count starts greater than 2.
182.
Description
Description
®
®
Intel
IXP45X and Intel
IXP46X Product Line of Network Processors
471) is
Table
181.
Table 182
illustrates
Developer's Manual
475
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