BBB TPS65217 RTC

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1

Does the BBB use the TPS65217 RTC to keep system time while powered, but not synchronized to any NTP server?

I’m not looking to maintain time between boots, just want to know the accuracy of the BBB system time while powered and not connected to the internet.

I’ve tried searching, but all results point to various ways of adding an external battery backed RTC.

If the TPS65217 RTC is used automatically by the OS, that would be great, but we’ve noticed that some units don’t keep time very well (ex: 1 min/15 hours or worse).

I’m using the following base image:
Debian GNU/Linux 8
rcn-ee.net console Debian Image 2016-02-11
4.1.18-ti-rt-r53 #1 SMP PREEMPT RT Thu Mar 17 19:41:07 UTC 2016 armv7l GNU/Linux

One of the changes I made was to use chrony as the time daemon. Perhaps I’ve misconfigured it that may result in bad time keeping.

2

Does the BBB use the TPS65217 RTC to keep system time while powered, but not synchronized to any NTP server?

No, the beaglebone uses the tsp65217c “real-time clock” to bring up the power rails on the beaglebone in the correct order, and all the other interresting power things. Such as charge batteries, etc. In other words, the tsp65217c is not a real-time clock. It’s a power management IC.

3

Is it possible to use the RTC component of it in the way I described? If so, what needs to be done?

Thank you for your help.

4

That part is a power management IC not a RTC there is a built in RTC in
the processor that will not keep
time when powered down.

5

Oh, my mistake. I was under the impression that part had a RTC, but lost time when powered down. See here: https://groups.google.com/forum/#!category-topic/beagleboard/vnu8sC9fgYo

In any case, if the RTC is in the processor, is there any way to enable it as I described? I’m interested in using it to keep more accurate time when power is ON; I have another means of setting the initial time correctly.

6

$ ls /sys/devices/platform/ocp/44e3e000.rtc/rtc
rtc0

7

By the way, you can use /dev/rtc0 just like any other real-time clock. Search the internet for “linux how to use real-time clock”

8

Rtc0 is already used by default…

9

That does not mean you can not set time on it, set time in apps from it, etc.

10

Absolutely. I’m familiar with some of this, but became confused recently as to whether a real RTC was in use when powered on or something less accurate. Anyone know the accuracy of rtc0? 50ppm?

11

that’s probably in the TRM.

12

Well actualy, it may be in the datasheet. For the am335x processor.