TK1 HDMI tuning registers - for FCC Class B testing

We have a TK1 based design that is failing FCC Class B limits on the HDMI output.
On googling, we came across a reference to “Tegra HDMI Tuning Guide”, but could not find the actual document.
Can we tune the HDMI output like signal drive, rise time etc?
Or can we enable spread spectrum? Does this help in lowering the emissions. The TRM does not give details on the spread spectrum, other than a single bit to enable/disable. Is there any data on this

Any feedback would be appreciated
Thank you

There are registers for drive strength, termination tuning…etc. Below are some related registers, you can check the details in TRM.


We enabled spread spectrum for PLL2 (driving HDMI) and we managed to clear Class B limits. But with spread spectrum enabled, the HDMI audio is not working.The Audio is from a different PLL.
Is this expected?Is there something else we need to do for Audio? We need to drive both Audio and Video.

Any feedback would be appreciated
Thank you


Could you share your modification?

This is our register configuration

Thank you

Hi Balajis,

Sorry for late reply.

Few questions for this issue.

  1. Is HDMI video working fine with PLL_D2?

  2. Is PLL_D2 the only change for your case?

  3. What’s the orclk and pixel clock? How much will it vary when spread spectrum is enabled?

  4. What’s your raster setting? Did you try different raster?