Keysight M8000 Series of BER Test Solutions User Guide 435
Setting up Patterns 7
Interactive Link Training
PCI Express 3.0/4.0 Testing
Interactive link training is required for link equalization testing as outlined
in the PCI Express (R) Architecture PHY Test Specification.
LTSSM (Link Training and Status State Machine)
Link Training and Status State Machine (LTSSM) is the sub-block that
drives and controls the link initialization, and training process for a PCIe
device to enable the normal data exchange between the two devices over
the link. LTSSM operates at the physical layer level and exchanges
physical layer packets (Ordered sets such as TS1 and TS2) to initialize,
train, and manage the link.
Two PCIe 3.0/4.0 instruments exchange Training Sequences as shown in
the following diagram:
Training Sequences are also used to switch the link to low power states.
LTSSM States
LTSSM transits through various states and sub states during link
initialization, training, and management. The entry and exit of each of
these states and the exchange of packets (Ordered sets) between the two
devices during each state is as per the PCIe specifications.
As per the PCIe specifications, LTSSM has 11 states and further
sub-states. These states are referred to frequently in this chapter to
describe LTSSM testing using the Keysight LTSSM Tester tool. Following is
a list of these states followed by a diagram to illustrate the sequence of
these states as per the PCIe specifications.
•Detect
• Quiet
•Polling
• Configuration
•L0
•Recovery
Device A Device B
TS TS TS TS
TS TS TS TS
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