BBAI RTC

[Chinmay Pendharkar]

Hello,

Does the BeagleBone AI have an onboard RTC? If so is there any documentation about it and how it can work? If there is a mechanism to add battery/supercap to keep time.

-Chinmay

[Steve Lentz]

I just spent the last few weeks looking at the BBB RTC.

If you want a battery backed RTC, you will need to add one.  The Maxim DS3231 is one example.  Adafruit makes several breakout boards and modules so you can pick your flavor of how you want to connect it.  The clock will be connected to the I2C - 2 bus.

Then add this line to /boot/uEnv.txt:

dtb_overlay=/lib/firmware/BB-I2C2-RTC-DS3231.dtbo

Restart, and that’s it.  Your BBB now has a battery backed RTC.  If it’s on a network and can reach an NTP server, it will set the RTC automagically.

The BBB still does not have a good low power sleep mode.  The RTC will not fix that, but it’s not the fault of the RTC, which otherwise works quite nicely with the Linux drivers.

-Steve

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[Chinmay Pendharkar]

Thanks Steve!

I have used external RTCs with BBB before. I was wondering if anything changed with the new Beaglebone AI. I can see some mention in the AM5729 datasheet, but not much on the BBAI System Reference documentation https://github.com/beagleboard/beaglebone-ai/wiki/System-Reference-Manual

-Chinmay

[Steve Lentz]

As I understand it, there is a hardware clock, but it is not backed up by battery.  If the BBB always has access to a network, that’s not a big deal, it can grab time from NTP and reset the clock.  

I’m planning to use the BBB in an underwater housing and power it off for days at a time to save battery, so I needed another solution for keeping time.  The DS3231 suits this purpose well.

After trying for a while with sleep modes, alarms, FETS, relays etc, I’ve decided I need a separate MCU to act as the timer to wake everything up when the BBB is powered down.  I just received some new parts from Adafruit, we’ll see how that goes.  

-Steve

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[Robert Nelson]

Careful everyone, Chinmay asked about the BB-AI, which is am57xx based.

Sorry, I haven't even looked up what the am57xx has for a RTC, we
definitely don't have a backup battery.

We will probably have to do something similar to the BBB, but rename
the node alias in the overlay to work with both am3/am5 boards..

Regarts,

--
Robert Nelson
https://rcn-ee.com/

[robert.sty...@gmail.com]

AM57X RTC is not connected to anything useful

On the schematic https://github.com/beagleboard/beaglebone-ai/blob/master/BeagleBone-AI_RevA2_sch.pdf

on sheet 5 location A3

[Chinmay Pendharkar]

Sorry folks if I'm asking in the wrong forum. I couldn't figure out how to tag the question as being for BB-AI.

-Chinmay

[robert.sty...@gmail.com]

The BeagleBone AI (BBAI) has the AM5729 system-on-chip.(which is part of the AM57xx series). The other BeagleBones have AM33xx series.

The AM5729 has a RTC peripheral built in. BUT, the BBAI does not have the necessary connections and components to use it.

If you need time of day, and do not have an internet connection to a time service, or a wake-up alarm; then you need an external add-on board.