Introduction
The probe for the Sierra M124/M122 does not re-drive or repeat the signal when in Analyzer mode. It operates transparently to introduce the minimum interference on the signal under test so that the dynamic equalization mechanisms in 12Gbps SAS will work as intended (T.A.P.3™ analog front-end [AFE] characteristics are described in detail in the technical brief; SAS Probing Methodologies). It is not necessary to perform probe calibration because the T.A.P.3 design does not actively re-drive the signal. However the signal beyond the T.A.P.3 circuit may be calibrated to improve the signal quality of the 12Gbps link as it's received by the analyzer. Conversely, when operating in Trainer (generator) or Infusion (jammer) mode, the Sierra M124/M122 is actively re-driving the signal. In this case, the Sierra M124/M122 may benefit from tuning the receiver and transmitter training if the link is not successfully negotiating to 12Gbps. It is essential to differentiate between "analyzer mode calibration" issues and "Trainer/Infusion mode link-up" issues.
| Optimizing Analyzer Receiver Ⓐ |
| In some cases, it may be necessary to perform calibration on the Sierra M124/M122 when using Analyzer mode. This may be evident when bit errors appear in the traffic captured by the analyzer even though the link is operating without issue. When using analyzer mode, there are two main issues that can affect analyzer operation. |
| Symptom: | Link is operating normally but errors appear in the trace (The signal beyond the T.A.P.3 circuit can be calibrated to improve the signal quality as it is received by the analyzer SERDES). | DUTs unable to establish 12Gbps link (Signal integrity issues on the DUTs receivers prevent link up or continually re‐train to 6Gbps; the only option is to try to improve the channel under test): |
| | 1) Use Auto Calibration: (see item 2)a) | 1) Use shorter cables |
| 2) Use Adv. Auto Calibration (see item 2)b) | 2) Use higher quality cables |
| | 3) Use different target or initiator |
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| Optimizing Trainer / Infusion Receiver & Transmitter Training Ⓣ Ⓙ |
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| In some cases, it may also be necessary to optimize transmitter and receiver training on the Sierra M124/M122 when using Trainer or Infusion mode. This may be evident when the DUTs are unable to establish or maintain 12Gbps link. These training parameters identified as "TxRxVout and Pre‐emphasis" can be tuned for the Sierra M124/M122 when in Trainer or Infusion mode (only). |
| Symptom: | DUTs unable to establish 12Gbps link (continually retrains or steps down to 6Gbps) |
| | 1) Use shorter cables |
| 2) Use higher quality cables |
| 3) Adjust Reference Probe Setting; (see item 3)a) |
| 4) Adjust TxRx Vout & Preemphasis; (see item 3)b) |
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Analyzer Calibration Procedure
The Auto Calibration and Advanced Auto Calibration features are available by selecting Setup > TxRx Vout & Preemphasis dialog. Both methods are automated and attempt to optimize the analyzer SERDES to "clean up" the received signal on the analyzer SERDES. Important notes:
- Both techniques only affect the analyzers interpretation of the signal under test and will not affect
link under test (this procedure will not resolve initial link up problems).
- Both modes require the system-under-test is powered and the link is established at the 12Gbps rate.
- Any changes in the link (cables/components) may require re-running calibration.
a. Auto Calibration
Standard Auto Calibration ❶ is performed by firmware, and it is relatively fast, but it may not resolve all
errors appearing in the trace. It is necessary for the system-under-test to be powered and link established at
the 12Gbps rate (data I/O not required). During calibration, the system will automatically adjust the DFE
values until it detects no running disparity or bit errors on the analyzer SERDES.
| Use the checkboxes to specify which links should be calibrated. |
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| The default time interval of 500 MS defines the elapsed time firmware will spend tuning and detecting errors. It can be increased if initial tuning is unsuccessful. |
If the default DFE settings of "0" are not automatically changed during calibration, it indicates the analyzer detected no errors during the initial calibration sequence. |
Use the Start button to initiate auto calibration. The dialog will report "Successful" for each port where no errors
are detected and "Unsuccessful" if errors were detected on any misbehaving ports. Upon completion of the calibration sequence, use the Close button to exit the Auto Calibration dialog. If the default settings were modified during calibration, it is recommended to use the Save button (which may be used at any time) to save the current DFE settings to a file. The 'Load' then 'Apply' button may be used to restore previously saved DFE settings.
Notes:
- Settings should be re-loaded using the 'Load' then 'Apply' buttons after shutting down the analyzer
- Calibrated DFE settings are specific to the channel tested and should be considered valid only when using the same or similar device/cable combinations.
- The "Start Reading Port Status" button provides a quick way to check the error rate after applying adjustments
In some cases, it may be desirable to calibrate only a single misbehaving port. Increasing the default time interval and re-running the auto calibration for the problematic link may resolve the issue (as shown below):
b. Advanced Auto Calibration
The Advanced Auto Calibration ❷ may be used if standard Auto Calibration does not resolve errors appearing in the trace. The Advanced calibration is performed by software and attempts to sweep through all combinations of DFE values. It is recommended that the default settings are used on the initial pass. Advanced Auto Calibration can take up to one hour for marginal links.
In some cases, Advanced Auto Calibration may not resolve all errors occurring in the trace. The time interval values may optionally be adjusted to increase the amount of time spent at each DFE value. The target eye width provides a mechanism to incrementally lower or raise the threshold that defines a valid signal. The default value of 50% is an aggressive setting. For additional margin, it's recommended to increase target eye-width to 60-70%. Use the Read Port Status button to quickly test the settings. If the Port Status error counter indicates that calibration is unable to remove the errors in analyzer mode, the only course of action is to replace cables and/or components in the system-under-test to reduce loss and improve the fidelity of the signal captured at the analyzer SERDES.
c. PMA (Physical Media Attachment) Analog Control Settings
The PMA analog control settings provides manual adjustment of (DC) gain and RX equalization control settings. These control are rarely needed as the auto‐calibration features above provide more granular adjustment. If Auto calibration is unsuccessful, increasing the DC gain can benefit the signal level interpreted by the Sierra system. These controls can be edited for each active link. Please contact PSG Support for additional assistance here.
Trainer / Infusion Receiver & Transmitter Training Procedure
In some cases, it may be necessary to tune the Training behavior when using the Sierra M124/M122 in Trainer or Infusion mode. This may be evident when the link fails to train at 12Gbps after the Sierra M124/122 is added to the line. (Recall that, when operating in Trainer or Infusion mode, the Sierra M124/M122 is an active participant in the link. In this mode, it's possible to manually override the default training behaviors on the Sierra system to improve link integrity within the channel-under-test.)
Using the Rx/Tx Settings window, there are two basic approaches to resolving connectivity problems when using Trainer or Infusion mode.
- Alter the default Reference values ❶ requested by the DUT during link training
- Alter the actual voltage & pre-emphasis using Advanced settings ❷ for each port on the Sierra system transmit path
It is recommended users start with the References ❶ option. The Advanced option ❷ requires manually altering voltage & pre-emphasis settings. Identifying the optimum settings is time-consuming and not recommended for novice users. Be advised that modifying the Sierra M122/M124 transmitter training as described below will alter the normal link training negotiation that occurs automatically. To return to normal "default" settings after using the apply button, it is necessary to use the "Restore Factory Settings" button which will restore defaults for both analyzer equalization and transmitter training.
a. References Probe Setting
To help tune the link training process, it's possible to alter the reference starting points that the Sierra platform will utilize during normal transmitter training. The References button opens a dialog that allows users to view the default reference values as defined by the SAS-3 specification. Changes to the values in this window effectively override the starting point for transmitter training specified by the far-end (ie: Coefficient Settings). After adjusting these values and resetting the link, the PHY on the Sierra platform will attempt to re-train normally and faithfully increment / decrement the training coefficients requested from the far-end; but these adjustments will be based on the altered starting point. This effectively allows the Trainer/Infusion PHYs to traverse a different range of values as the far-end receiver attempts to clean-up the signal eye. It is recommended to follow the basic sequence below.
- After problems with 12Gbps training (Trainer/Infusion mode), disconnect the SAS cable from the Sierra system.
- Click the References button to open the dialog (below).
- The Reference to be modified depends on the initial Coefficient_Settings requested by the DUTs. If the DUT specifies Reference 2, the user should override these values by replacing with one of the other Reference settings. For example, if the DUT specifies Reference 2, the user should copy all four values ❶ from Reference 1 to Reference 2 (as shown below) to override the Reference 2 starting point.
- Click OK. In the TX/RX Settings window, Check Disable RX Training and click Apply. Reconnect the SAS cable to the Sierra system and check 12gbps link status. If successfully linking at 12Gbps, save these settings using Save button for future use.
- If unsuccessfully linking at 12Gbps, open the References dialog again.
- Repeat the procedure by copying the values ❷ from NoEq to Reference 2 (leave the Reference 1 as is).
Overriding the reference values as described above will affect all links connected to the Sierra Trainer / Infusion system. If the Trainer / Infusion is now successfully connecting at 12Gbps with the DUT, the training sequence has been successfully optimized. Check Disable RX Training to force the Trainer / Infusion link procedure to ignore normal receiver training and instead use the saved values. If the reference value procedure above is not successful, it is possible to manually select other reference values. Alternatively, it is also possible to manually select the TX / RX voltage for the transmitter and receiver on each port of the Sierra using the Advanced option below. Transmitside equalization (referred to as TxEQ) can be also be specified manually here. Due to large number of possible values, this procedure (outlined below) is not recommended without Teledyne LeCroy support assistance.
b. Advanced Settings
The Advanced button opens a Probe Setting dialog that allows users to set the TX Signal parameters. The tap values are coefficients that control a discrete-time adaptive high-pass filter within the transmit path of the Sierra Trainer / Infusion system. Tip: Capture a complete trace of the link training sequence to determine if there is only a single physical port that fails to train (may be evident in the trace by no TRAIN DONE primitive or no 12G traffic from problematic link). This allows users to focus their efforts on a single link.
- To adjust TXRxVout, select Setup > TxRx Vout & Preemphasis to display the V. Rx/Tx Settings dialog (below).
- Highlight the Port that is desired to change.
- Press the Read button ❶ to read the current values for all ports (these will be the last values achieved through automatic Training. These values are preserved in registers on the Sierra system after every link training attempt.)
- Press the Advanced button ❷ to see and adjust the values. The typical set of values for the Iniato are shown in the VI Advanced probe setting dialog. To edit the values for a different port, click Cancel. Select the desired port on the Rx/Tx Setting dialog and then click the Advanced button (no need to re-read the values).
- Manipulate the "Pre-emphasis first" and "Pre-emphasis pre-tap" fields by making small changes to the previously used values. This is an iterative process to eliminate errors. After each value change, click OK.
- Click the Overwrite TX Settings checkbox ❶ to retain the values specified through manual transmitter training settings (this will ensure the link uses the specified values after each power cycle or link disconnect).
- Press Apply❷ in the Rx/Tx Settings dialog to write the new value to the Sierra platform SERDES. Reconnect the link and monitor link bring-up to determine if the two sides successfully complete training. If the Trainer / Infusion is now successfully connecting at 12Gbps with the DUT, the training sequence has been successfully optimized. Note: If using analyzer mode to record 12Gbps traffic and invalid bit errors appear in the trace, it may be necessary to also perform "auto calibration" as defined on page 2.
