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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
August 2006
Developer’s Manual
Order Number: 306262--, Revision: 004US
421
USB 2.0 Host Controller—Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
The LastStart line was calculated in this example to assume the absolute worst-case
bus overhead per transaction. The particular transaction used was a start-split, zero-
length OUT transaction with a handshake. A summary of the component parts are listed
Table 171, “Example Worst-Case Transaction Timing Components” on page 421
. The
component times were derived from the protocol timings defined in the USB
Specification Revision 2.0.
Figure 56.
Best Fit Approximation
Packet Size in Bytes
80% Threshold
Last Start
f(x)
Byte
Times
to
EOF
7000
6000
5000
4000
3000
2000
1000
0
B4474-01
1 64 127 190 253 316 379 442 505 568 631 694 757 820 883 946 1009
Transactions that
will be started
Transactions that will be skipped
Goal is to minimize area under this curve
Table 171.
Example Worst-Case Transaction Timing Components (Sheet 1 of 2)
Component
Bit
Time
Byte Time
Explanation
Split Token
76
9.5
Split token as defined in USB core specification. Includes sync,
token, eop, etc.
Host 2 Host IPG
88
11
Number of bit times required between consecutive host packets.
Token
67
8.375
Token as defined in USB core specification. Includes sync, token,
eop, etc.
Host 2 Host IPG
88
11
Same as above.
Data Packet (0
data bytes)
66.7
8.34
Zero-length data packet. Includes sync, PID, crc16, eop, etc.