topic Re: Question, i.MX28 RTC in i.MX Processors

Question, i.MX28 RTC

Aemj — Wed, 30 Mar 2016 02:42:28 GMT

Dear team,

I would like to ask about RTC inside of i.MX28.

The issue is seen on my customer’s lab.

The issue is RTC gains 50 seconds per 7 hours.

The issue occurs on the customer’s board and EVK as well.

They use LinuxBSP, L2.6.35_1.1.0.

The source clock of RTC is 32.768KHz crystal.

The procedure to see the RTC is as below.

- Right after Boot-up,

Set-up system clock by ‘date’ command.

Copy the date to RTC by ‘hwclock –w’ command.

- Left for 7 hours.

- Get system clock by ‘date’ command.

- Get RTC by ‘hwclock’ command.

As the result,

The system clock seems to be right, but RTC gains 50 seconds.

Do you have any ideas on the cause of this phenomenon?

Thanks,

Miyamoto

Re: Question, i.MX28 RTC

Yuri — Wed, 30 Mar 2016 09:05:56 GMT

Hello,

Basically, RTC accuracy is fully defined by accuracy of the external crystal.

Nevertheless, please try using 24 MHz as RTC source.

Have a great day,
Yuri

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

Re: Question, i.MX28 RTC

Aemj — Fri, 01 Apr 2016 02:18:50 GMT

Hi Yuri,

The customer believes that using 24MHz for RTC source is not possible for their application, because they have to use battery-backup mode. In that mode, 24MHz clock cannot be used for RTC, right?

The customer thinks that the 32.768KHz crystal signal is weak and it can be affected by a noise from internal DCDC. Because they saw the issue did not occur when i.MX28 is in back-up mode.

Is it possible for you to reproduce the issue on your EVK?

Here is the procedure that they did.

The customer saw this phenomenon occur on your EVK as well.

For i.MX28 EVK, they use LinuxBSP L2.6.35. And they did the following command to switch RTC clock source to 32.768KHz.

memtool 80056064=00000021

Thanks,

Miyamoto

Re: Question, i.MX28 RTC

Yuri — Mon, 11 Apr 2016 05:44:27 GMT

Hello,

Have You tried just to use sysfs interface ?

$cat /sys/class/rtc/rtc0/date

$ cat /sys/class/rtc/rtc0/time

Regards,

Yuri.

Re: Question, i.MX28 RTC

Yuri — Tue, 12 Apr 2016 02:13:18 GMT

Hello,

I found on my i.MX28 EVK drift of several seconds per day.

To decrease it one can use more stable crystal / oscillator

or perform calibration for each board.

Regards,

Yuri.

Re: Question, i.MX28 RTC

Aemj — Tue, 12 Apr 2016 02:32:31 GMT

Hi Yuri,

Thanks a lot for your support.

OK, I will tell it to my customer.

Thanks,

Miyamoto