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On Stratix IV device, is it a must to connect ALTGX_RECONFIG module to ALTGX IP which is confiured as "transmitter only" mode?


We used ALTGX IP on Stratix IV GX device, it's configured as "basic PMA direct" and "transmitter only" mode.

We didn't add ALTGX_RECONFIG module. We infer that ALTGX_RECONFIG module is mainly for receiver offset cancellation. This design works fine in the past 4 years.

But recently we encountered 8 failure cases of CMU PLL unlock.

We tried to add ALTGX_RECOFNIG module in this design, and found that CMU PLL is locked after adding RECONFIG module.

Has anyone encountered similar problem? We are not sure whether this is the root cause of CMU PLL unlock. Because this design has worked fine for 4 years without RECONFIG module.


Many tks!​

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2 Replies

Hi Glen,


As I understand it, you have some inquiries related to the ALT_RECONFIG instance for TX only ALTGX instance. For your information, you would need to connect the ALT_RECONFIG to the ALTGX even though your ALTGX is configured in TX only mode. I believe there are some calibration process required for the XCVR to work as expected. You may refer to the "Offset Cancellation Feature" section in the SIV device handbook vol 2. You may find description as following:


"For the Transmitter only configuration, the ALTGX_RECONFIG must also be connected to the ALTGX by either selecting a dynamic reconfiguration mode or instantiating a dummy Receiver only ALTGX instance in each side of the device."


Please let me know if there is any concern. Thank you.


Chee Pin


Hi Chee Pin,

Thansk for your advice!

Seems that we have missed some key points in handbook (It would be better if QII can report an error when RECONFIG is absent).

We will add ALTGX_RECONFIG module in the design.

Many thanks!


Best regards,


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