16.3. Link Training
The Physical Layer automatically performs link training and initialization without software intervention. This is a well-defined process to configure and initialize the device's Physical Layer and link so that PCIe packets can be transmitted. If you encounter link training issues, viewing the actual data in hardware should help you determine the root cause. You can use the following tools to provide hardware visibility:
- Signal Tap Embedded Logic Analyzer
- Third-party PCIe protocol analyzer
You can use Signal Tap Embedded Logic Analyzer to diagnose the LTSSM state transitions that are occurring on the PIPE interface. The ltssmstate bus encodes the status of LTSSM. The LTSSM state machine reflects the Physical Layer’s progress through the link training process. For a complete description of the states these signals encode, refer to Reset, Status, and Link Training Signals. When link training completes successfully and the link is up, the LTSSM should remain stable in the L0 state. When link issues occur, you can monitor ltssmstate to determine the cause.
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