Keysight Technologies U4301, User Manual

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Keysight U4301 PCIe Gen3 Analyzer User’s Guide 35
Setting the Capture Options 4
Getting non-overlapped data in the trace even when the Bidirectional Trimming was set to On
The following are examples of some specific situations when you get non-overlapped data for the
two directions even if you enable the Trim non-overlapped data option.
Descrambler (Gen1 / Gen2) Tells the analyzer whether the descrambler algorithm is necessary:
• Enabled — activates the descrambler algorithm. This algorithm generates the descrambled packet stream
from an incoming scrambled packet stream.
• Disabled — deactivates the descrambler algorithm. Select this option when the DUT is transmitting the
non-scrambled data.
Garbage data is displayed if this is set incorrectly.
L0s Testing Lets you select whether or not the U4301A/B module will capture packets in the L0s state.
• Enabled - When you enable the L0s Testing option, the U4301A/B module captures packets in the L0s state and
the power management testing capabilities are enabled and enhanced in terms of :
• improvement in locking time
• faster data capture while coming out of the electrical idle
• Disabled - When you disable the L0s Testing option, the power management testing capabilities are available
but not enhanced.
Bidirectional Trimming As the name suggests, the Bidirectional Trimming feature is useful only for bidirectional data capture setups.
The following two options are available for the Bidirectional Trimming field:
• Trim non-overlapped data - Select this option if you want the U4301 Analyzer to trim extra packets
(non-overlapped data) from both the directions of a bidirectional data capture. An example where this option is
particularly useful is when one of the directions is transmitting large data packets compared to the relatively
smaller packets transmitted by the other direction. This results in the memory being filled up quicker for one of
the directions and therefore overlapping bidirectional data is visible only around the Trigger in the trace. The
start and end of the trace have non-overlapping and non-correlated data. To overcome this problem, you can
choose to enable bidirectional trimming that trims the extra packets at the start and end of the trace making the
trace more useful for analysis.
If you enable the Trim non-overlapped data option and U4301 does not find any overlapping data for the two
directions, then it captures the non-overlapping data for both the directions instead of generating an empty trace
with no data.
See Also
See “ Getting non-overlapped data in the trace even when the Bidirectional Trimming was set to On ” on
page 35.
• Off - Select this option if you want the U4301 Analyzer to also capture extra packets (non-overlapped data) from
both the directions of a bidirectional data capture. The resulting data capture may have an uneven start and end
of trace for the two directions with extra upstream / downstream packets captured at the start / end of the trace.
You may want to turn off the Bidirectional trimming in troubleshooting situations, for example, when a link stops
working. In such situations, extra packets may help in analyzing the cause of the problem.
Trim Last Packet The following two options are available for this field:
• Enabled - Select this option if you want the U4301 Analyzer to trim the last packet from the trace. At times, the
last packet in the trace may not get captured completely and therefore you may want to trim this packet by
selecting this option.
• Disabled - Select this option if you want the U4301 Analyzer to keep the last packet in the trace as is.
Lane Alignment The following two options are available for the Lane Alignment field:
• Strict - Select this option if you want the U4301 Analyzer to start storing the data only after the lane alignment
has been achieved, that is, after the block alignment in case of Gen 3 and after the symbol alignment in case of
Gen 1/Gen 2. Any data prior to lane alignment is then ignored thereby avoiding the storage of data with
misaligned lanes.
• Relaxed - Select this option if you want the U4301 Analyzer to start storing the data even before the lanes have
been aligned, that is, prior to the block alignment in case of Gen 3 and the symbol alignment in case of Gen
1/Gen 2. Any data including packets when coming out of Electrical Idle, bit errors, and training sequences with
lanes not aligned are also stored.
NOTE : The Relaxed mode is primarily used in troubleshooting scenarios that involve the data before the lane
alignment and therefore some of the features such as triggering may not work as expected when using the
relaxed mode.
Field Description