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Adventurer
Adventurer
4,181 Views
Registered: ‎12-20-2010

ZCU102 real time clock is drifting

The Zynq Ultrascale+ real time clock (RTC) on the ZCU102 board is drifting by about 20 minutes per day.  This is well beyond the drift that might be attributed to inaccuracy of the 32.768KHz (20ppm) crystal that clocks the RTC.

 

The RTC contains a calibration register (CALIB_WRITE) that stores the value that is used to generate one second based on the oscillator period.  Can anyone tell me how that register value is calculated?   It is returning a value of 0x198223, but based on the 32.768KHz clock, I was expecting the value to be 32,768 (0x8000).

 

Is there anything else that would account for the large drift we are seeing in the RTC?

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6 Replies
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Moderator
Moderator
4,119 Views
Registered: ‎02-16-2010

The RTC has a calibration feature that should be able to compensate fractional inaccuracy. Take a look at the RTC Module Register Database.
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Adventurer
Adventurer
4,114 Views
Registered: ‎12-20-2010

Thanks for the suggestion, but I believe the fractional compensation will compensate for minor drifts of 1 or 2 seconds per day.  We are seeing drifts of 20 minutes per day.

 

We are still unable to find any documentation that explains how the calibration register (CALIB_WRITE) is calculated.  As I explained in my first post, CALIB_WRITE is returning a value of 0x198223, but based on the 32.768KHz clock, we are expecting the value to be 32,768 (0x8000).

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Highlighted
1,084 Views
Registered: ‎02-07-2008

Hi @kinkeads

 

I'm having this same issue and wondering if you eventually found a solution.

 

I seem to be getting much more drift than you are, in the order of a few hours a day.

 

Thanks.

 

Jeff

 

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Adventurer
Adventurer
1,072 Views
Registered: ‎12-20-2010

Sorry no, we have not found a fix to the clock drift. 

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Explorer
Explorer
756 Views
Registered: ‎11-12-2007

Are there any updates to this issue?

We have similar problem: The clock on out ZCU102 is skipping one second after every power restart.

So the more we powercycle the board, the RTC is skipping more time.

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Contributor
Contributor
540 Views
Registered: ‎09-18-2018

Also having the same issue, can someone from Xilinx guide us to the right direction?

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