HDMI Reference Design FR_CLK

[JLee25]

Hi all,

  I am curious to know the requirement of this fr_clk mentioned in C10 GX HDMI UG, https://www.intel.com/content/www/us/en/programmable/documentation/ezu1511767661589.html.

My question is what frequency should be used for this purpose?

Can I use 100 MHz instead of this 625MHz?

As I noticed the design file use "300 MHz" instead of "625MHz"..

Please let me know.

Thank you!

BRs,

Johnson

[Deshi_Intel]

Hi,

fr_clk is the transceiver power on calibration pll refclk source for HDMI Tx and CDR refclk0 for HDMI Rx.

It's recommended to follow back example design to use 300MHz.

Thanks.

Regards,

dlim

[JLee25]

Hi dlim.

  Thank you for the reply!

What bothers me is the clock did not exist in the old reference design..

And I have a design following the old without this fr_clk..

And it's not possible to add this as all the clock pins are used.

Therefore would you check if this fr_clk is a must?

BRs,

Johnson

[Deshi_Intel]

Hi Johnson,

Your understanding is correct.

This is new feature where we added in latest HDMI IP example design in case customer required quick transceiver power up calibration process.

If you don't have such concern then it's totally fine to ignore it.

• Pls modify gxb_rx NativePHY IP to change default CDR refclk from 0 to 1
• CDR refclk 0 is the FR_CLK that you want to bypass while CDR refclk 1 is the TMDS clk that HDMI is using

Thanks.

Regards,

dlim

[Deshi_Intel · Accepted solution]

HI Johnson,

On 2nd thought, I think you can still connect fr_clk while providing whatever clk frequency that's available on your board. Eg : 100MHz.

I found out more info. It should still works as stated from below A10 HDMI example design guideline doc that explained on fr_clk functionality.

• Free running clock (625 MHz) for primary transceiver reference clock. This clock is required for transceiver calibration during power-up state. This clock can be of any frequency. 
• https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/ug/ug-hdmi-de.pdf

Thanks.

Regards,

dlim