LS1046 SGMII Clock - 100 vs 125MHZ serdes clock

[matthej]

Hi,

We are using the SGMII interface at 1Gbps and have the choice of using a 125MHz or 100MHz SerDes clock to run these interfaces.

Right now, I have the clocks at 100MHz in my design. I was wondering if there is any performance differences between running at 100MHZ vs 125MHz in my design?

I could run both clocks in a different clock port I suppose and then run whichever I need to

Thanks!

[yipingwang]

You could refer to LS1046ARDB to configure SERDES Reference Clocks as the following.

SD1_CLK1 = 156.25MHZ, SD1_CLK2 = 100.00MHZ

[matthej]

Thanks for your response.

My question is if I am using 3 SerDes lines for SGMII and I want to provide the LS1046 with both a 100MHz and 125MHZ which are valid clocks for this interface, how do I select which PLL to use to select the correct clock?

SD1_REF_CLK1: 100MHz

SD2_REF_CLK2: 125MHZ.

From the picture above it looks like I am able to select either REFCLK1 or REFLCK2 for PLL2 but only REFCLK1 for PLL1.

How do I select which PLL to use for this interface and am I correct in assuming that I am able to use either 100MHZ or 125MHZ clock for my current setup?