AM3354: RTC accuracy

Koichiro Tashiro

Part Number: AM3354

Hi,

My customer is evaluating AM3354 RTC and checked the accuracy of the calendar.
He found +15min differences in 6 hours. (6 hours in real time vs 6 hours 15min in RTC)
This is more than 4% error and I think it is too much.

The RTC clock is RTC32KCLK(32k_aux_clk) from Peripheral PLL.
The RTC is running in Functional mode.

What are potential causes of such big errors?

Thanks and regards,
Koichiro Tashiro

over 5 years ago

0 Biser Gatchev-XID over 5 years ago

TI__Guru**** 393215 points

Hi,

What is the OSC0 frequency?

0 Koichiro Tashiro over 5 years ago in reply to Biser Gatchev-XID

TI__Mastermind 22945 points

Hi Biser,

Customer uses 25MHz.

Thanks and regards,
Koichiro Tashiro

0 Biser Gatchev-XID over 5 years ago in reply to Koichiro Tashiro

TI__Guru**** 393215 points

There is something wrong in the system configuration. It seems that the system is behaving as if it's running from 24MHz. 25/24MHz = 1.04166... which is exactly the time difference you observe. First thing to check is SYSBOOT[15:14] values. For 25MHz you need to set SYSBOOT[15:14] = 10b.

0 Koichiro Tashiro over 5 years ago in reply to Biser Gatchev-XID

TI__Mastermind 22945 points

Biser,

Customer checked sysboot[15:14].
The value is 10b as expected.
They checked both pin states and control_status register.

Do you have any other points to check?

Thanks and regards,
Koichiro Tashiro

0 Biser Gatchev-XID over 5 years ago in reply to Koichiro Tashiro

TI__Guru**** 393215 points

Other thing to check is software. What software are they using? Which version?

0 Koichiro Tashiro over 5 years ago in reply to Biser Gatchev-XID

TI__Mastermind 22945 points

Biser,

Customer found an error in PRCM register.
After the register is fixed, no RTC error is observed.
Thanks for your support on this.

Thanks and regards,
Koichiro Tashiro

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AM3354: RTC accuracy