Teledyne LeCroy USB Protocol Suite User Manual (Voyager_Advisor T3_Mercury) - Manual (Page 272)

Teledyne LeCroy Corporation Recording Options‐Misc. USB 2.0
272 USB Protocol Suite User Manual
10.3.1 Analyzer Trace Speed
This option sets the speed of the traffic recorded by the Analyzer. The default setting is
Auto‐detect. This setting tells the Analyzer to discover what speed traffic is running and
to label packets accordingly. Auto‐Detect will find a speed and lock on it permanently for
the duration of the trace. If traffic speed changes, it will not be seen by the analyzer. If
you are having problems with your recordings, you might try setting the traffic speed to
one of the fixed values ‐‐ Low, Full, and Hi speed. These settings are used when you want
to manually set the traffic speed. It can take ~ 6 ms for the High Speed detection to occur
in Auto‐Detect mode, so it is possible to miss some packets with this method.
In some rare cases, auto‐detection circuitry causes Full Speed devices to fail to
enumerate on plug‐in. Changing the Analyzer speed to Full Speed can sometimes solve
this problem.
Setting the speed to one of the fixed values is sometimes useful for debugging purposes.
For example, if a device that is producing numerous errors at a particular speed, you may
wish to set the recording to that speed in order to ensure that the Analyzer does not
misread the error packets and label them the wrong speed. While it is unlikely that the
Analyzer will mislabel packets in this way, manually setting the recording speed
guarantees that the Analyzer always records packets at the correct speed.
When selecting a fixed speed, the analyzer will stay on that speed regardless of traffic. To
capture more than one speed requires looping through multiple 2.0 ports (USBTracer or 2
daisy chained analyzers such as Voyager or Advisor T3)
Notes on Hi Speed Recordings
Erroneous chirp blocks can be recorded on an idle bus when the Device has its FS
terminations on while the Host has HS terminations connected. This causes a small
differential voltage (“tiny‐J”) on the USB bus that causes false Chirp detection.
This condition occurs during speed negotiation:
 On a HS bus, the condition is momentary just before the device chirps.
 On a CS bus, the condition occurs both before and after the device chirp (until
the end of Reset). The user is discouraged from using Speed=HIGH to record sig‐
nals on a classic speed bus.
 The Analyzer stops recording anything for 2.5 milliseconds following a FS_K state
(which is at least 2 microseconds long). This is to avoid presenting “garbage”
which is a by‐product of the high‐speed probe settling down.