RTC issue: voltage is applied to battery but it does not provide enough power to save RTC

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1

Hi to everyone, especially to those who did manage to fit battery for
saving RTC state.
I've also managed to do it but battery does not provide enough power
to save RTC state. What I see when i measuring voltage on battery is
3.1V of charging (board is powerd up), then i unplug power and measure
voltage again and see 2.4V, after that i power up board and see
following message in dmesg:

[ 6.507080] twl_rtc twl_rtc: Power up reset detected.
[ 6.533111] twl_rtc twl_rtc: Enabling TWL-RTC.
[ 6.556915] twl_rtc twl_rtc: rtc core: registered twl_rtc as rtc0

So, the main question is, what voltage should be on the battery to
save RTC state, and the next question how long should it be charged to
this voltage. Thank you for your answers.

2

The 3.1V you see is the charge voltage. The 2.4V you see is the battery voltage. Per the TPS65950 datasheet, it has to be 1.5V minimum. So, 2.4V is enough. How long it takes to charge depends on the size of the battery.

You do however, need to enable the RTC inside the TPS65950 from a SW standpoint. So your issue may be related to that.

Gerald

3

You do however, need to enable the RTC inside the TPS65950 from a SW> standpoint. So your issue may be related to that.

Ok, is it special magic or cast? I just find nothing how to enable RTC
inside TPS65950 in mail-list or somewhere else. What does 'SW
standpoint' is? I just cant get it, sorry. I did not dive deep into
this topic.

4

This issue is resolved by a SW change in your code. I am the Hardware (HW) guy. Take a look here.

http://groups.google.com/group/beagleboard/search?group=beagleboard&q=RTC

Gerald

5

Thanks, Gerald, i have already read this posts previously.

It seems to me that RTC on beagleboard-xm not working right now as designed.

6

It does indeed work. People have successfully used it in the past. What your specific issue is, I can’t say.

Gerald

7

Well, looking for the person who have rtc-enabled beagleboard…

8

In message <27480544.86.1329332141748.JavaMail.geo-discussion-forums@ynii32>

9

O, this is new information for me about RISC OS. So did you try
Angstrom linux on beagleboard and rtc running?

10

In message
<CAHKdsmRdCmd29z2s_B3EMa-MG1vOR-dur9TwLXDFqBRh_ks4Lw@mail.gmail.com>

11

Ok, i see so from the RISC OS rtc is working fine? Right? Could you
measure voltage on the battery when board is powered down? Just want
to compare with mine.

12

In message
<CAHKdsmT+XUzK7v5drXK-HH-0LMapE2HrUjdNv_GiLGV+Wcr8xQ@mail.gmail.com>

13

Hi, Dave

thanks for the responce.

Could you measure voltage when board is powered up?