Troubleshooting IP Connection Issues Star-Ultra Equipment And SpacefibreLight

This document details the investigation into connection problems between Star-Ultra equipment and SpacefibreLight IP within a CNES (Centre National d'Études Spatiales) environment. The primary issue observed is the failure of the IP connection, leading to a series of diagnostic steps and analysis to pinpoint the root cause. This troubleshooting process involves examining signal behavior, identifying anomalies in data transmission, and analyzing PLL (Phase-Locked Loop) locking status. The goal is to provide a comprehensive understanding of the problem and propose actionable solutions to restore the connection.

1. Initial Setup and Problem Statement

The initial setup involves both the Star-Ultra equipment and the SpacefibreLight IP being held in a reset lane state. The core problem arises when the Star-Ultra device continuously sends IDLE WORDs upon detecting the disconnection of the SpacefibreLight's High-Speed Serial Link (HSSL). This behavior indicates a potential issue in the communication protocol or hardware synchronization between the two devices. To diagnose the issue, a series of tests and analyses were performed to identify the cause of the connection failure. The images provided serve as crucial visual aids, capturing the state and behavior of the devices during different phases of the troubleshooting process. Understanding the initial conditions and the observed symptoms is critical in formulating a targeted approach to resolve the IP connectivity problem between these critical components.

2. Testing Procedure and Observations

The testing procedure commenced with the Star-Ultra equipment enabling its lane, with the link set to start. The trigger was set to lane mode. Despite these configurations, no trigger was initiated, which was anticipated given the SpacefibreLight lane's inactive state. This initial test confirms that the Star-Ultra equipment correctly responds to the SpacefibreLight's disconnection by not initiating a trigger. Subsequently, the SpacefibreLight IP was configured to disable lane reset and start the lane, which resulted in a trigger being performed. This contrasting behavior is a critical observation, highlighting that the SpacefibreLight lane state directly influences the trigger mechanism. The primary issue lies in the handshake or synchronization process between the Star-Ultra and SpacefibreLight during lane startup. By meticulously testing various lane states and observing the resulting triggers, we can begin to isolate the point of failure in the communication link. These controlled tests are essential for building a clear picture of the interaction between the two devices and identifying the precise conditions under which the connection fails.

3. Analysis of SpacefibreLight PHY Enablement

3.1 Unexpected Data Counter Behavior

In the analysis phase, enabling the SpacefibreLight PHY (Physical Layer) revealed unexpected behavior. Ideally, the SpacefibreLight should continuously transmit INIT1 words upon PHY enablement. However, the observed behavior deviated from this expectation. Instead of a continuous stream of INIT1 words, a data counter was transmitted up to a value of 0x3F, followed by INIT1 words, and then the counter again, creating a recurring pattern. This deviation is a significant anomaly, suggesting a potential issue in the PHY's initialization sequence or data transmission logic. The intermittent transmission of the counter instead of the continuous INIT1 words may indicate a problem in the state machine controlling the PHY's behavior, or a misconfiguration in the data transmission settings.

3.2 Implications of Irregular INIT1 Transmission

The irregularities in the INIT1 transmission can disrupt the initial handshaking process required for establishing a stable connection. The Star-Ultra equipment might not properly synchronize with the SpacefibreLight if the expected INIT1 stream is not consistently present. This failure in synchronization can lead to the observed IP connection issues. Further investigation is necessary to determine the cause of the counter insertion and ensure that the PHY adheres to the standard initialization protocol. Identifying and resolving this issue is crucial for establishing a reliable link between the two devices. It may require examining the firmware or hardware configuration of the SpacefibreLight IP to ensure it conforms to the expected behavior.

4. Star-Ultra State Transitions and Signal Loss

Further analysis of the communication sequence revealed that the Star-Ultra equipment transitions into the INIT2 state after some exchanges. This is a normal part of the initialization process, indicating that the Star-Ultra is attempting to establish a link. However, following the INIT2 state, the Star-Ultra reverts back to the IDLE state. This reversion is likely caused by signal loss, suggesting that the link establishment process is interrupted before it can complete. The loss of signal may stem from various factors, including intermittent connectivity, signal attenuation, or synchronization problems. Understanding the root cause of the signal loss is crucial to preventing the repeated transitions and stabilizing the connection. This requires examining the physical layer connections, signal integrity, and synchronization mechanisms to pinpoint the exact point of failure.

4.1 Repetitive Sequence and PRBS Word Insertion

The aforementioned sequence, involving transitions to INIT2 and subsequent reversion to IDLE, repeats multiple times. Eventually, the data stream is replaced by PRBS (Pseudo-Random Binary Sequence) words, which are added to the counter. This insertion of PRBS words suggests that the system is attempting to perform link diagnostics or testing due to the persistent connection failures. The repeated sequence indicates a continuous effort to establish a link, which ultimately fails, leading to the diagnostic mode activation. This behavior highlights the severity of the underlying issue and the system's inability to maintain a stable connection. The repetitive nature of the failure underscores the necessity of identifying and addressing the root cause to ensure reliable communication.

4.2 Persistent Failure and Diagnostic Mode

This sequence, involving PRBS word insertion, repeats far more times than the initial sequence, leading to the same outcome – a failure to establish a stable connection. This prolonged failure further emphasizes the need for a comprehensive diagnosis. The system's inability to maintain a link, even after numerous attempts and diagnostic procedures, points to a fundamental issue that needs to be resolved. The diagnostic mode, characterized by PRBS word insertion, is a response to the repeated failures, but it does not address the core problem. Therefore, a thorough investigation into the underlying cause of the connection failures is essential for implementing an effective solution.

5. PLL Lock Status Analysis

5.1 Unlocked PLL and Its Implications

The analysis of the PLL (Phase-Locked Loop) lock status revealed that it consistently remains at 0, indicating that the PLL is not locking. This is a significant issue, as a locked PLL is essential for stable frequency synchronization between the Star-Ultra and SpacefibreLight. An unlocked PLL can lead to unreliable data transmission and connection instability. The PLL is responsible for generating the precise timing signals required for high-speed communication, and its failure to lock suggests a fundamental problem in the synchronization process. This issue could stem from various factors, including frequency mismatches, signal integrity problems, or PLL circuit malfunctions.

5.2 PLL Locking Requirement in Lane Loopback Scenario

In a lane_loopback_farend scenario, the PLL is expected to be locked. The fact that it remains unlocked in this configuration is a clear indication of a critical failure. The lane loopback scenario is designed to test the integrity of the communication link by sending and receiving signals within the same lane. A locked PLL is necessary for this test to function correctly. The consistent unlocking of the PLL highlights a core synchronization issue that needs to be addressed. This may involve examining the PLL's configuration, input signals, and loop parameters to identify the root cause of the locking failure. A stable and locked PLL is crucial for reliable high-speed communication, and its persistent unlocking is a key factor contributing to the overall connection issues.

6. Conclusion and Proposed Solutions

6.1 Identifying and Addressing the Counter Issue

In conclusion, the investigation reveals two primary issues contributing to the IP connection problems between the Star-Ultra equipment and SpacefibreLight IP. First, the origin of the counter up to 0x3F needs to be identified. This counter disrupts the expected continuous transmission of INIT1 words, which is crucial for establishing the initial handshake. The counter should be removed or replaced with continuous IDLE words to ensure proper synchronization during the PHY enablement phase. Tracing the source of this counter may involve examining the firmware or hardware configuration of the SpacefibreLight IP. Ensuring the correct and continuous transmission of INIT1 words is vital for a stable connection.

6.2 Resolving PLL Locking Problems

Second, the cause of the PLL not locking must be identified and resolved. The unlocked PLL indicates a fundamental synchronization problem that prevents the establishment of a stable communication link. This may involve a detailed analysis of the PLL's input signals, loop parameters, and overall circuit health. Potential issues could include frequency mismatches, signal integrity problems, or component malfunctions within the PLL circuit. A locked PLL is essential for reliable high-speed data transmission, and resolving this issue is crucial for restoring the IP connection. Addressing both the counter issue and the PLL locking problem will significantly improve the reliability and stability of the communication between the Star-Ultra equipment and SpacefibreLight IP.

To summarize, the following steps should be taken:

1. Identify the source of the counter up to 0x3F within the SpacefibreLight IP.
2. Remove or replace the counter with continuous IDLE words.
3. Investigate and resolve the PLL locking issue, ensuring stable frequency synchronization.

By addressing these key issues, the IP connection problems between the Star-Ultra equipment and SpacefibreLight IP can be effectively resolved, leading to a more stable and reliable communication link.