Best Fit Approximation; Example Worst-Case Transaction Timing Components - Intel IXP45X Developer's Manual

USB 2.0 Host Controller—Intel
Figure 56.

Best Fit Approximation

7000
6000
5000
Byte
Times
to
4000
EOF
3000
2000
1000
0
1 64 127
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
in Table 171, "Example Worst-Case Transaction Timing Components" on page
component times were derived from the protocol timings defined in the USB
Specification Revision 2.0.
Table 171. Example Worst-Case Transaction Timing Components (Sheet 1 of 2)
Component
Split Token
Host 2 Host IPG
Token
Host 2 Host IPG
Data Packet (0
data bytes)
August 2006
Order Number: 306262--, Revision: 004US
® ®
IXP45X and Intel IXP46X Product Line of Network Processors
Transactions that
will be started
Transactions that will be skipped
190 253 316 379 442
Packet Size in Bytes
80% Threshold
Bit
Byte Time
Time
76 9.5
88 11
67 8.375
88 11
66.7 8.34
Goal is to minimize area under this curve
505 568 631 694
Last Start
Split token as defined in USB core specification. Includes sync,
token, eop, etc.
Number of bit times required between consecutive host packets.
Token as defined in USB core specification. Includes sync, token,
eop, etc.
Same as above.
Zero-length data packet. Includes sync, PID, crc16, eop, etc.
® ®
Intel IXP45X and Intel IXP46X Product Line of Network Processors
757 820 883 946
f(x)
B4474-01
421. The
Explanation
Developer's Manual
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