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9 Viewing LTSSM States and State Transitions
98 Keysight U4301 PCIe Gen3 Analyzer User’s Guide
LTSSM Overview
Link Training and Status State Machine (LTSSM) drives and controls the link initialization and
training process for a PCIe device to enable the normal data exchange between the two PCIe devices
over the link. LTSSM operates at the physical layer level and transits through various states and
substates during link initialization, training, and management. During each of these states,
appropriate physical layer packets (training sequences) are exchanged between the link partners to
initialize, train, and manage the link.
To begin communication with a PCIe device, the link training process must complete successfully.
This makes link training one of the most crucial process in testing and validating a DUT. The
participation in the equalization procedure at Gen 3 speed makes this process more challenging to
test and validate.
The LTSSM Overview pane in the Protocol Viewer window of the Logic and Protocol Analyzer GUI helps
you in verifying the link training process and finding out reasons for any failure in this process. This
pane provides an overview of the link training process by displaying:
• a sequential list of the LTSSM states and their transitions.
• equalization summary in terms of the number and values of equalization transmitter coefficients
exchanged in TS frames found in the trace.
To display these states, transitions and equalization summary, the software analyzes a user-specified
data range or the entire data captured in a trace and presents the list of transitions/states/EQ data,
from that trace.