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geopa
Observer
Observer
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Registered: ‎10-30-2015

USB & Ethernet PHYs reference clocks through PS_MIO pins

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Hello,

I need to support both USB3 and Gigabit Ethernet on a Zynq Ultrascale+ device. I verified that I can use in parallel GEM3 and USB0, without conflict on the MIOs.

Preferably I would like to clock both PHYs from the Zynq PS (PS_MIO 44 & 45, or other unused ones) and not from external oscillators. This means I need to generate 25MHz and 26/19.2MHz (for Ethernet and USB respectively) with max +-50ppm frequency tolerance and <100ps jitter.

I fail to find relevant information on if that's even possible. Do I miss something basic? I understand that the common case is to use external oscillators, but I would really like to avoid doing so if possible.

I repeat that I am not referring to the ULPI's input clock, or the RGMII's Rx and Tx clocks, but to the output reference clocks that clock the PHYs.

Thanks in advance,
Giorgos

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nanz
Moderator
Moderator
384 Views
Registered: ‎08-25-2009

Hi @geopa ,

From Ethernet side, you can have your reference clock on PS MIO pins. Then GEM needs a 125MHz reference clock which will be generated by an internal RPLL or IOPLL. 

If you look into clock configuration for PS, you should be find each configuration and select which ref clock to use for GEM.


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If starting with Versal take a look at our Versal Design Process Hub and our Versal Blogs and our Versal Ethernet Sticky Note.

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nanz
Moderator
Moderator
385 Views
Registered: ‎08-25-2009

Hi @geopa ,

From Ethernet side, you can have your reference clock on PS MIO pins. Then GEM needs a 125MHz reference clock which will be generated by an internal RPLL or IOPLL. 

If you look into clock configuration for PS, you should be find each configuration and select which ref clock to use for GEM.


-------------------------------------------------------------------------------------------

Don’t forget to reply, kudo, and accept as solution.

If starting with Versal take a look at our Versal Design Process Hub and our Versal Blogs and our Versal Ethernet Sticky Note.

-------------------------------------------------------------------------------------------

View solution in original post

geopa
Observer
Observer
360 Views
Registered: ‎10-30-2015

Hi nanz,

it's been a while but thanks for your reply : )

I could not bring up Ethernet when using larger than ~700B MTU. When I switched to an external crystal the problem was solved, but maybe I was missing something else.

BR

Giorgos

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