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AM3359 system time mutation

shanqing liu
Intellectual 635 points
Other Parts Discussed in Thread: AM3359

Hi,

   I am testing my board based on AM3359. But I got a problem.

My board working 1 day or less time ,the system time wil mutaion.

Sometimes back 1 hour ,sometimes back 1 day.

I am use an external RTC (DS3231MZ).

I am also execute the command "date ' and "hwclock -r",the system time and the hw time are same , all of them are changed.

So ,would you please help me to resolve the problem?

Thank you very much.

Best Regards,

Liu

  • 0
    TI__Guru**** 393215 points

    Hi Liu,

    You should check if your external RTC is working OK, since you say that it's also changed.

  • 0 in reply to Biser Gatchev-XID
    TI__Guru 62945 points

    Please read Advisory 1.0.30 in the AM335x Silicon Errata.  The problem you describe sounds similar to symptoms seen when debugging this issue.

    Regards,
    Paul

  • 0 in reply to peaves
    Intellectual 635 points
    Thank you for your replying.
    First, I am sure that the external RTC is work normal. Everytime the board power on the system time is normal.
    I have read Advisory 1.0.30 in the AM335x Silicon Errata. You mean that the OSC0_GND and OSC1_GND should be connected to digital GND directly,right? This is exactly my HW bug, I am design reference starter kit board, so this errata is Ignored. But I don't think it is the really reason that causing this error. If noise interfere the crystal circuit, I think it only changed the system time even my system run error but the external RTC.

    The silicon errata said "The higher impedance connection through the AM335x device to the PCB digital ground makes it easier for electrical noise to couple into the crystal circuit. If the noise is large enough, it is possible that the oscillator output may produce clock glitches to various internal logic circuits. These clock glitches may cause unexpected behavior."

    Only the system time and external RTC is changed and more than once. There is no other "unexpected behavior".

    Am I right?

    Looking forward to your reply.
    Thank you very much.
    Best Regards,
    Liu
  • 0 in reply to shanqing liu
    Intellectual 635 points
    Can anyone help me?
    Thank you.
  • 0 in reply to shanqing liu
    TI__Guru 62945 points
    I'm not sure if I understand you last reply. In the first paragraph you say the external RTC is correct because the time is always correct when you turn on the board. However, in your third paragraph you say the external RTC and system time are changing.

    Are you saying the external RTC maintains the correct time while the board is powered down, but the external RTC and system clock is changing when the board it powered up? If not, please explain why the two paragraphs seem contradictory with respect to the external RTC.

    I assume the external RTC has its own clock and power source. If so, the only way it should change is software updating it to match the system clock. The system clock may be changing due to the noise issue described in my previous post. The first system found with this noise issue only had one symptom, the system time would randomly jump forward and back in time. Some customers with this issue found the time jumps could be improved or eliminated by changing the system timer clock source.

    Is you system clock being sourced from OSC0 (master oscillator) or OSC1?

    Have you resolved the crystal circuit ground connections as described in Advisory 1.0.30 to see if this helped?

    Regards,
    Paul