Troubleshooting Star-Ultra And Spacefibrelight IP Connection Issues

This article delves into the troubleshooting process for IP connection issues encountered between Star-Ultra and Spacefibrelight equipment, specifically within CNES and spacefibrelight environments. We will dissect the problem, analyze captured data, and propose potential solutions to restore a stable connection. The focus is on understanding the behavior of both devices during the connection establishment phase and pinpointing the root cause of the failure.

Initially, both the Star-Ultra equipment and the Spacefibrelight IP are held in a reset lane state. This means that their high-speed serial links (HSSL) are inactive, and no data transmission is occurring. The critical observation is that the Star-Ultra device continuously sends IDLE WORDs whenever the Spacefibrelight disconnects its HSSL. This behavior suggests that Star-Ultra is attempting to maintain a link, but the disconnection triggers a state where it defaults to transmitting idle signals.

The testing procedure involves a series of steps designed to isolate the source of the connection problem. The tests reveal valuable insights into how the devices interact during link initialization.

Initial Test: Star-Ultra Lane Enablement

Initially, the Star-Ultra lane is enabled, and the link is set to start. The trigger is configured for lane mode. However, no trigger occurs, which is expected since the Spacefibrelight lane is deliberately stopped. This step confirms that Star-Ultra is correctly configured to initiate a link when enabled.

Second Test: Spacefibrelight Lane Activation

The Spacefibrelight IP then has its lane reset disabled, and the lane is started. This action results in a trigger, indicating that Spacefibrelight is now attempting to establish a link. This test confirms that Spacefibrelight can initiate a link establishment sequence.

The analysis focuses on the communication patterns observed when Spacefibrelight attempts to establish a link. The captured data reveals several deviations from the expected behavior, providing clues about the connection issue.

1. Spacefibrelight PHY Enablement and Initial Word Transmission

When Spacefibrelight enables its PHY (physical layer), it is expected to send INIT1 words continuously. However, instead of continuous INIT1 words, a data counter is transmitted, incrementing up to a value of 0x3F. After reaching 0x3F, an INIT1 word is sent, followed by the counter again, and then another INIT1 word. This unusual sequence of counter values interspersed with INIT1 words is the first significant deviation from the expected protocol.

This behavior could indicate a problem with the Spacefibrelight's initialization sequence or a misunderstanding in how it should transition to the link establishment phase. It is crucial to determine why the device is sending a counter instead of the required continuous INIT1 words. Understanding this counter sequence is paramount to resolving the issue.

2. Star-Ultra's Transition to INIT2

After some exchanges, Star-Ultra transitions to the INIT2 state. This indicates that it has received some valid signals from Spacefibrelight and is progressing in the link establishment process. However, the subsequent behavior suggests that the process is not completing successfully.

3. Return to IDLE State

Following the transition to INIT2, Star-Ultra reverts to the IDLE state. This likely occurs because the signal is lost or becomes unstable. The loss of signal suggests a problem with the physical link or the ongoing communication between the devices. This could be due to signal integrity issues, timing mismatches, or other low-level communication problems.

4. Repetition of the Sequence with Data and PRBS Words

The previous sequence of INIT1, counter, INIT2, and IDLE repeats multiple times. Eventually, data words are replaced by Pseudo-Random Binary Sequence (PRBS) words, which are added to the counter. This suggests that the devices are attempting to synchronize and establish a reliable link, but the process is failing. The introduction of PRBS words often indicates a testing or debugging mode where the devices are attempting to evaluate the link's quality.

5. Persistent Repetition with PRBS Words

This sequence of PRBS words and the counter repeats far more times than the previous sequence. However, the outcome remains the same: the link cannot be established. The repeated failures highlight the persistence of the underlying problem and the need for a more thorough investigation.

6. PLL Lock Status

The Phase-Locked Loop (PLL) lock sequence remains at 0, indicating that the PLL is not locked. A locked PLL is essential for stable high-speed communication because it provides a clean and synchronized clock signal. The fact that the PLL is not locking is a critical clue. In a lane loopback far-end scenario, the PLL should be locked, suggesting a potential hardware or configuration issue.

Based on the analysis of the captured data, the primary issues appear to be related to the initial word transmission from Spacefibrelight and the inability of the PLL to lock. To effectively troubleshoot these IP connection issues between Star-Ultra and Spacefibrelight equipment, a focused approach is required.

Key Issues Identified

1. Counter Instead of Continuous INIT1: The root cause of Spacefibrelight transmitting a counter sequence up to 0x3F instead of continuous INIT1 words needs to be identified and rectified. This is a critical deviation from the expected protocol and is likely preventing the successful establishment of the link. This could be a firmware bug, a configuration error, or a hardware issue.
2. PLL Lock Failure: The PLL not locking is another major concern. A stable clock signal is essential for reliable high-speed communication. Investigate why the PLL is not locking, especially since it should lock in the lane loopback far-end scenario. This could involve checking power supply stability, clock signal integrity, and PLL configuration settings.

Recommendations for Resolution

1. Identify the Origin of the Counter: Investigate the Spacefibrelight firmware or hardware to determine why the counter is being transmitted. Replace this behavior with the correct continuous INIT1 word transmission as per the protocol specification. This requires a deep dive into the Spacefibrelight's PHY layer implementation.
2. Determine the Cause of PLL Unlocking: Investigate the reasons behind the PLL not locking. This may involve examining the power supply, clock signals, and PLL configuration. Ensure that the clock signal is stable and within the required frequency range. Verify that the PLL is correctly configured for the operating frequency and mode.

Further Troubleshooting Steps

• Signal Integrity Checks: Perform signal integrity checks on the physical link between Star-Ultra and Spacefibrelight. Ensure that the signal levels, impedance matching, and termination are correct. Use an oscilloscope or a signal analyzer to examine the signal waveforms.
• Clock Signal Analysis: Analyze the clock signals used by both devices. Ensure that the clock frequencies are accurate and stable. Check for jitter or other clock-related issues that could be preventing PLL lock.
• Power Supply Verification: Verify that the power supplies to both Star-Ultra and Spacefibrelight are stable and within the specified voltage range. Power supply issues can often lead to PLL unlocking and communication failures.
• Firmware Review: Review the firmware of both devices for any bugs or configuration errors related to link establishment and PLL control. Consult the device documentation and specifications to ensure correct configuration.
• Hardware Inspection: Inspect the hardware for any physical damage or defects, such as loose connections or damaged components.

By systematically addressing these recommendations, you can identify and resolve the IP connection issues between the Star-Ultra and Spacefibrelight equipment, leading to a stable and reliable communication link. The key is to address the fundamental issues of the incorrect initial word transmission and the PLL lock failure. These steps will help in diagnosing and resolving the connection problems effectively. Remember that a stable link is crucial for reliable data transfer in CNES and spacefibrelight systems.