Teledyne LeCroy USBTracer_Trainer - Users Manual - Manual (Page 108)

Chapter 5: Reading a Trace USB Protocol Suite User Manual
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LeCroy Corporation
5.1.1 USB 3.0 Packets
USB 3.0 has the following packet types:
•
Link Commands (Flow Control)
• Link Training Sequences (TS1, TS2, TSEQ)
• Logical Idle Packets
• Upstream Packets
• Downstream Packets
• Skip Sequences
• ISO Time Stamp Packets
• Inter-Packet Symbols (unexpected packets)
• Link Commands (other than Flow Control)
• LMP Packets
• Electrical Idles
• LFPS Packets
• Termination Packets (Time stamped when termination is detected by Analyzer)
5.1.2 Packet Direction
The Packet Direction field displays the direction the packet or signal was traveling on the
bus: Downstream from a Host or Upstream from a Device .
In most cases, direction can be determined unambiguously. However, some signals and
situations, including protocol errors, cannot be determined with high confidence, since
either Host or Device might be responsible for them. Such cases are marked as
Question Marks in the trace.
Rather than mis-identfying the signal, the software requires you to determine direction
(or note an error condition, which experience has shown is rare). In most cases, you can
assume the direction based on the sequence of events that occurred.