giacomo gasparini

T1024 Single Clock mode

Discussion created by giacomo gasparini on Jun 10, 2020
Latest reply on Jun 10, 2020 by giacomo gasparini


Actually we are using the CPU with the following clock fed but we have problems with SerDes locking at startup:

- 100MHz 1.8V DC-LVDS clock to DIFF_SYSCLK_P/N inputs;

- 100MHz 2.5V AC-LVPECL clock to SD1_REF_CLK1_P/N inputs;

- 100MHz 2.5V AC-LVPECL clock to SD1_REF_CLK2_P/N inputs;



In from RM is written that:

In this mode, single onboard oscillator can provide the reference clock (100MHz) to the
following PLLs:
• Platform PLL
• Core PLLs
SerDes PLLs


In fig. 4-3 "single oscillator mode", from RM: the 2x SerDes PLL are feed externally;


In 4.1.1, datasheet it's written:

When using Single Oscillator Source clocking mode, a single onboard oscillator can provide the reference clock (100 MHz) to all the PLLs (that is, Platform PLL, CoreCluster PLLs, DDR PLL, USB PLL and SerDes PLLs).


In table 138, datasheet it's written:

"Single Oscillator Source" Reference clock mode supports differential reference clock pair frequency of 100 MHz.


In 4.1.7, datasheet it's written:

The clock ratio between each of the two SerDes PLLs and their respective externally supplied SD1_REF_CLKn_P/SD1_REF_CLKn_N inputs is determined by [...]



- is it true that SerDes PLL1/2 could be feed from ONLY one reference 100MHz differential clock (DIFF_SYSCLK_P/N) in "Single Oscillator Source clocking mode"?

- How can we enable "Single Oscillator Source clocking mode"?

Thank you.