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Contributor
Contributor
166 Views
Registered: ‎10-28-2018

How the VCU's reference clock is configured?

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Hi,

I'm trying to get the VCU to work on zcu104 board,

The document pg252 seems vague about the reference clock of the VCU PLL input.

There is a "CORE Clk(MHz)" option to set the core clk frequency in the config wizard.

I indeed can set it to 667 to maximize the performance, but according to the pg252,figure 7-1, this clk come from the vcu pll, which have the input "pll ref clk":

Screenshot from 2019-04-18 12-07-31.png Screenshot from 2019-04-18 12-10-31.png

The doc says " The range of the PLL reference clock is 27 to 60 MHz " and nothing more. 

But as far as I know, the pll output is proportional to the pll input, what the internal logic controls is only the proportion, as given in the doc:

Fvco = Frefclk × M

Fclkout = Fvco / O

But the input is not fixed according to the doc, and I did not see how the VCU PLL knows the input frequency value.

Only I saw @sebo in This post mentioned the TRD used 33.333Mhz as the pll_ref_clk frequency.

And I found someone mentioned device tree in this QA .  but I did not see detailed information in pg252 for device tree setup.

then how do user get Fclkout that he wants and set the pll_ref_clk correctly?

 

 

Regards,
Kang
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Contributor
Contributor
126 Views
Registered: ‎10-28-2018

Re: How the VCU's reference clock is configured?

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I exported the hdf file and generated a petalinux project, configured the project with the hdf (the information is located in a hwh file inside the hdf),

after build the kernel, I guess the generated device tree pl.dtsi have the information which is used in linux vcu driver:

Screenshot from 2019-04-18 15-27-44.png

Hi @sebo,

FYI

 

Regards,
Kang
2 Replies
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Explorer
Explorer
137 Views
Registered: ‎03-17-2011

Re: How the VCU's reference clock is configured?

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hi @hu_kang 

Just to mention that I've also used the VCU with a ref clock input at 50MHz, and in some other tests a clock from the PS (<-- which is not recommended).

 

--Sebastien
Contributor
Contributor
127 Views
Registered: ‎10-28-2018

Re: How the VCU's reference clock is configured?

Jump to solution

I exported the hdf file and generated a petalinux project, configured the project with the hdf (the information is located in a hwh file inside the hdf),

after build the kernel, I guess the generated device tree pl.dtsi have the information which is used in linux vcu driver:

Screenshot from 2019-04-18 15-27-44.png

Hi @sebo,

FYI

 

Regards,
Kang