AM335x RTC stops when VDD_CORE is switched off.

Matti Kaasinen

Hi!

I experienced above problem with my first prototype card whose processor was silicon version 1.0. I got my processor upgraded to silicon version 2.1 (AM3352BZCZ). However, same feature seems to be still present. According to errata (http://www.ti.com/lit/er/sprz360g/sprz360g.pdf) this should have been fixed in silicon revisions 2.0 and 2.1.

Vdd_core and vdd_mpu are switched OFF but vdd_rtc is ON. Is there anything more I should do - or have I anyhow got silicon revision 1.0 in spite of the package markings?

Thanks,

Matti

over 9 years ago

0 Biser Gatchev-XID over 9 years ago

TI__Guru**** 393215 points

Hi,

This would depend on the way CAP_VDD_RTC is connected. If you have connected this pin to the VDD_CORE power rail and RTC_KALDO_ENn is tied to VDDS_RTC, this means that the internal RTC LDO is not used and RTC-only mode is not possible. See processors.wiki.ti.com/.../AM335x_Schematic_Checklist for the different RTC use cases and connections

0 Matti Kaasinen over 9 years ago in reply to Biser Gatchev-XID

Intellectual 660 points

Connection is like your link describes for RTC-only mode. Only deviation is that RTC_KALDO_ENn is grounded through 10 kohm resistor. CAP_VDD_RTC terminal is connected with 1 uF decoupling capacitor to VSS.

0 Biser Gatchev-XID over 9 years ago in reply to Matti Kaasinen

TI__Guru**** 393215 points

That seems to be correct then. Have you checked what happens to RTC_PWRONRSTn when you switch the supplies off? It must stay high.

0 Matti Kaasinen over 9 years ago in reply to Biser Gatchev-XID

Intellectual 660 points

It is connected to VDD_RTC, so it stays HIGH.

0 Biser Gatchev-XID over 9 years ago in reply to Matti Kaasinen

TI__Guru**** 393215 points

Can you provide more details: what PMIC are you using, what software, how do you stop power supplies?

0 Matti Kaasinen over 9 years ago in reply to Biser Gatchev-XID

Intellectual 660 points

We have TPS65217CRSLR PMIC installed on our board that is running on Linux 4.1.22 RT kernel (Linux-ti-staging-rt_4.1) built using Yocto/Poky distribution whose TI specific stuff is coming from meta-ti layer (fido). This specific feature happens for instance if I execute: "sthutdown -h now". I switch supply off when terminal reports: reboot: System halted.

I made more measurements. It seems that behavior is no quite as I explained but: Time RTC provides after boot is what it is written before shutdown - either manually by hwclock command or by operation system transferring system time to RTC. So, it does not halt to time it had at shutdown - it provides some time older time that time at shutdown. So, this is possible some kind of SW problem - how RTC is driven.

Thanks,
Matti

0 Biser Gatchev-XID over 9 years ago in reply to Matti Kaasinen

TI__Guru**** 393215 points

That seems to show that the RTC is maintaining the time value at least. A thing that you should check is the RTC clock source - this is configured in the RTC_OSC_REG and by default the external oscillator is disabled.

0 Matti Kaasinen over 9 years ago in reply to Biser Gatchev-XID

Intellectual 660 points

It appears that settings to RTC_OSC_REG are executed in probe function of rtc-omap.c module. It seems that device tree needs to have "ext-clk-src" symbol defined in order to get external oscillator activated. I inserted that, but operation seems still the same. RTC starts after boot with time that has been stored somehow to RTC. RTC does not advance during poweroff.

I suppose I Should now as Arago distribution for this?

Thanks,

Matti

0 Biser Gatchev-XID over 9 years ago in reply to Matti Kaasinen

TI__Guru**** 393215 points

This is the link to the Linux RT SDK: software-dl.ti.com/.../index_FDS.html Kernel version is v4.1.18.

0 Matti Kaasinen over 9 years ago in reply to Biser Gatchev-XID

Intellectual 660 points

Ok, thanks. In fact I had written my version wrongly. It is v4.1.13. So there is something to update.

0 Matti Kaasinen over 9 years ago in reply to Matti Kaasinen

Intellectual 660 points

I updated to Linux kernel v4.1.18 - it did not help. Then I compiled RTC kernel driver to kernel (originally loadable module). That worked.
As a summary for operations that I believe as necessary to get this working:
1) add ext-clk-src symbol to rtc section of device tree (see git.ti.com/.../rtc-omap.txt)
2) compile RTC driver into kernel ==>
CONFIG_RTC_DRV_OMAP=m
to
CONFIG_RTC_DRV_OMAP=y

0 Matti Kaasinen over 9 years ago in reply to Matti Kaasinen

Intellectual 660 points

Thanks Biser, you pushed me to correct direction!

0 Biser Gatchev-XID over 9 years ago in reply to Matti Kaasinen

TI__Guru**** 393215 points

Thanks for posting your results on the forum, Matti! I'm glad you resolved this issue.

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AM335x RTC stops when VDD_CORE is switched off.