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Real Time Clock

Nye, Philip
I am getting reports of the system clock on the Gumstix (overo earth storm) losing big jumps of time - hours or days. This is most likely happening during power cycles though I have not been able to catch it happening. The overo is on our own board which has a non-rechargeable 3V lithium coin cell backing up the RTC.

Does anyone else have experience of anything like this? or pointers to what might be happening?

Is there anything in the backup battery circuitry which could cause the backup battery to drain at an abnormal rate? I know the circuit will trickle-charge a rechargeable cell and ours has a series diode to prevent unwanted back current.

Philip


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Re: Real Time Clock

mwynne

I have seen this with the AirSTORM. I tried using some rechargeable 123A lithium cells thinking they would last for long periods of being powered off, but they didn't. Then I tried a regular lithium 2032 button cell and those were dead in a matter of several days. I thought they might heat up and explode because there does seem to be voltage at the RTC Vbackup, though the current must be extremely small because they didn't even get warm. That might explain why the relatively large lithium cells didn't really charge.

Since then I've moved to the recommended Lithium Vanadium Pentoxide rechargeable battery (http://wiki.gumstix.org/index.php?title=Coin_cell). It's very small, but seems to last as long as the others I've tried. Though I haven't conducted extensive testing yet. I have 10 units with this battery and I think I've only seen one go dead and loose the time after being powered off for about 3-4 days. The bottom line is these batteries should be lasting longer. I can leave a desktop PC unplugged for a month and a small battery will keep the RTC going, so what's the deal with these COM's?

At this point I have other projects to worry about, but I intend to investigate further when I can. If anyone can offer any other suggestions I would also be grateful.

-michael

On Aug 5, 2013 5:31 PM, "Nye, Philip" <[hidden email]> wrote:
I am getting reports of the system clock on the Gumstix (overo earth storm) losing big jumps of time - hours or days. This is most likely happening during power cycles though I have not been able to catch it happening. The overo is on our own board which has a non-rechargeable 3V lithium coin cell backing up the RTC.

Does anyone else have experience of anything like this? or pointers to what might be happening?

Is there anything in the backup battery circuitry which could cause the backup battery to drain at an abnormal rate? I know the circuit will trickle-charge a rechargeable cell and ours has a series diode to prevent unwanted back current.

Philip


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Re: Real Time Clock

Jonathan Kunkee
I haven't dealt with the RTCs on Gumstixen, so I'm curious:

What voltage does the RTC expect?
What's the forward drop of your charger-blocking diode? (It sounds like a low-enough current application that a GaAs or germanium diode would work fine, with their lower forward voltages.)
Have you measured the peak current consumption of the not-otherwise-powered RTC? What is the I-V curve of the battery like? (L-Ions are usually able to keep a steady voltage over a wide range of peak loads, but I'm used to bigger ones.)

If the questions are good food for thought, I'm glad; if the information gets shared here, all the better.

Good luck,
Jon Kunkee


On Mon, Aug 5, 2013 at 10:33 PM, Michael Wynne <[hidden email]> wrote:

I have seen this with the AirSTORM. I tried using some rechargeable 123A lithium cells thinking they would last for long periods of being powered off, but they didn't. Then I tried a regular lithium 2032 button cell and those were dead in a matter of several days. I thought they might heat up and explode because there does seem to be voltage at the RTC Vbackup, though the current must be extremely small because they didn't even get warm. That might explain why the relatively large lithium cells didn't really charge.

Since then I've moved to the recommended Lithium Vanadium Pentoxide rechargeable battery (http://wiki.gumstix.org/index.php?title=Coin_cell). It's very small, but seems to last as long as the others I've tried. Though I haven't conducted extensive testing yet. I have 10 units with this battery and I think I've only seen one go dead and loose the time after being powered off for about 3-4 days. The bottom line is these batteries should be lasting longer. I can leave a desktop PC unplugged for a month and a small battery will keep the RTC going, so what's the deal with these COM's?

At this point I have other projects to worry about, but I intend to investigate further when I can. If anyone can offer any other suggestions I would also be grateful.

-michael

On Aug 5, 2013 5:31 PM, "Nye, Philip" <[hidden email]> wrote:
I am getting reports of the system clock on the Gumstix (overo earth storm) losing big jumps of time - hours or days. This is most likely happening during power cycles though I have not been able to catch it happening. The overo is on our own board which has a non-rechargeable 3V lithium coin cell backing up the RTC.

Does anyone else have experience of anything like this? or pointers to what might be happening?

Is there anything in the backup battery circuitry which could cause the backup battery to drain at an abnormal rate? I know the circuit will trickle-charge a rechargeable cell and ours has a series diode to prevent unwanted back current.

Philip


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Re: Real Time Clock

Akram Hameed
In reply to this post by mwynne
Hi Michael,

Have had the same sort of issues as you.

Default gumstix kernel enables charging on the RTC coin cell circuit. It's a 50uA rate though, so exceptionally slow.  I'd definitely either turn off the charging (recompile kernel) or forget about using throw away lithium cells. Risky!

With regards to rechargeables: I found that if I bumped things up to the max charge rate, the Lithium vanadium pentoxide cell lasts a month or so (I have not measured past that) with no power. Mostly my problem was that the conservative charging rate that is the default in the kernel does not feed the cell very fast, and thus you need to leave the damned thing on for days to get a charge.

I have experienced a complete loss of time when unmating a TOBI board from a custom carrier board (board loaded up with 2000-01-01 time, which presumably suggests dodgy time in RTC memory). I suspect something shorts a bit when that occurs.  Be careful of noise, therefore, on any expansion headers. 

The other thing I've noticed, which may help Philip, is that on shutdown (depending on your rootfs/kernel) the system attempts to flush systime to the hwclock. As a result of this, if anything goes even a little pear-shaped on a shutdown (let's say your power supply starts going down a little faster than you expect), I have found that a completely dodgy value can be pushed out to the clock. 

My thought was it might be a bad i2c transaction (the amount of time 'shift' as a result of this power-down dodginess was about 12-24 hours). Which I believe amounted to about 1 bit of rot.  Never got around to debugging properly, however. Instead, I avoid writing to the RTC during any situations where my system power supply might be even a little bit dodgy.

Hope this helps.

Cheers,

Akram



On Tue, Aug 6, 2013 at 2:33 PM, Michael Wynne <[hidden email]> wrote:

I have seen this with the AirSTORM. I tried using some rechargeable 123A lithium cells thinking they would last for long periods of being powered off, but they didn't. Then I tried a regular lithium 2032 button cell and those were dead in a matter of several days. I thought they might heat up and explode because there does seem to be voltage at the RTC Vbackup, though the current must be extremely small because they didn't even get warm. That might explain why the relatively large lithium cells didn't really charge.

Since then I've moved to the recommended Lithium Vanadium Pentoxide rechargeable battery (http://wiki.gumstix.org/index.php?title=Coin_cell). It's very small, but seems to last as long as the others I've tried. Though I haven't conducted extensive testing yet. I have 10 units with this battery and I think I've only seen one go dead and loose the time after being powered off for about 3-4 days. The bottom line is these batteries should be lasting longer. I can leave a desktop PC unplugged for a month and a small battery will keep the RTC going, so what's the deal with these COM's?

At this point I have other projects to worry about, but I intend to investigate further when I can. If anyone can offer any other suggestions I would also be grateful.

-michael

On Aug 5, 2013 5:31 PM, "Nye, Philip" <[hidden email]> wrote:
I am getting reports of the system clock on the Gumstix (overo earth storm) losing big jumps of time - hours or days. This is most likely happening during power cycles though I have not been able to catch it happening. The overo is on our own board which has a non-rechargeable 3V lithium coin cell backing up the RTC.

Does anyone else have experience of anything like this? or pointers to what might be happening?

Is there anything in the backup battery circuitry which could cause the backup battery to drain at an abnormal rate? I know the circuit will trickle-charge a rechargeable cell and ours has a series diode to prevent unwanted back current.

Philip


------------------------------------------------------------------------------
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Re: Real Time Clock

Eric Diethorn
In reply to this post by Nye, Philip
Hi Philip (and others on this thread),

My colleagues and I have spent quite a lot of time on the RTC over the past months, for the same reason. Using FIRE COMs and IronSTORM COMs, we saw the button battery fail to support the RTC within 10 to 20 days after a full charge when our widget was powered off for that period of time. We did modify uImage to max-out the charging current to 500 ua. This at least provides a full charge within several hours of continuous operation, but the bottom line is the battery's capacity to support the RTC is limited. We made measurements of the current draw on the coin battery when the Overo is off. This draw is 10 uA (once the RTC is initially programmed during a prior boot session). Given that the coin battery (Panasonic ML621S) has a capacity of 5 mA-hours, this results in an estimated RTC life on the shelf of about 500 hours, or about 21 days. Because the RTC loses functionality at a voltage that is greater than the end capacity voltage of the coin battery, we are seeing an RTC shelf life of between 10 and 20 days.

To get around this problem, we added a simple circuit consisting of two diode drops and a 1 kOhm resistor between the main battery (2000 mA-hrs in our widget) and the button battery. So, we use the main battery to charge the button battery. This is not without risks of overcharging, however, so we are monitoring things at this point.

Eric
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Re: Real Time Clock

Paul D. DeRocco
> From: Eric Diethorn [mailto:[hidden email]]
>
> My colleagues and I have spent quite a lot of time on the RTC
> over the past
> months, for the same reason. Using FIRE COMs and IronSTORM
> COMs, we saw the
> button battery fail to support the RTC within 10 to 20 days
> after a full
> charge when our widget was powered off for that period of time. We did
> modify uImage to max-out the charging current to 500 ua.

So what programs the charging registers? You say uImage, Akram mentioned the
kernel. I'd like to boost the charge current, too. What source file do I
patch? I'm using AirSTORM at the moment, if that matters, and a pretty
up-to-date Yocto/Dylan build.

--

Ciao,               Paul D. DeRocco
Paul                mailto:[hidden email]


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Re: Real Time Clock

Ash Charles
In reply to this post by Akram Hameed
On Mon, Aug 5, 2013 at 11:10 PM, Akram Hameed <[hidden email]> wrote:
> Default gumstix kernel enables charging on the RTC coin cell circuit. It's a
> 50uA rate though, so exceptionally slow.  I'd definitely either turn off the
> charging (recompile kernel) or forget about using throw away lithium cells.
> Risky!

For what it's worth, I could bump up the default charge rate for the
Gumstix kernels.  Does this cause problems or help anyone out?  IIRC,
it is set low just to be safe.

--Ash

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Re: Real Time Clock

Paul D. DeRocco
> From: Ash Charles [mailto:[hidden email]]
>
> For what it's worth, I could bump up the default charge rate for the
> Gumstix kernels.  Does this cause problems or help anyone out?  IIRC,
> it is set low just to be safe.

Isn't there some way to make this configurable through menuconfig, or by
supplying a configuration fragment? (A proc file interface would be even
better, but it's probably not worth going to that much trouble.)

Meanwhile, what kernel source file contains this stuff, so I can hack mine
today?

--

Ciao,               Paul D. DeRocco
Paul                mailto:[hidden email]


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Re: Real Time Clock

Ash Charles
Hi Paul,

The trickle charging is enabled by CONFIG_RTC_DRV_TWL4030.  In the
Linux source code, the driver can be found in
<linux>/drivers/rtc/rtc-twl.c
(https://github.com/gumstix/linux/blob/omap-3.2/drivers/rtc/rtc-twl.c)

In the probe function, you can see some code along the lines of
        /* enable backup battery charging */
        /* use a conservative 25uA @ 3.1V */
        ret = twl_i2c_write_u8(TWL4030_MODULE_PM_RECEIVER,
                BIT_PM_RECEIVER_BB_CFG_BBCHEN |
                BIT_PM_RECEIVER_BB_CFG_BBSEL_3V1 |
                BIT_PM_RECEIVER_BB_CFG_BBISEL_25UA,
                REG_BB_CFG);

--Ash

On Thu, Aug 8, 2013 at 9:39 AM, Paul D. DeRocco <[hidden email]> wrote:

>> From: Ash Charles [mailto:[hidden email]]
>>
>> For what it's worth, I could bump up the default charge rate for the
>> Gumstix kernels.  Does this cause problems or help anyone out?  IIRC,
>> it is set low just to be safe.
>
> Isn't there some way to make this configurable through menuconfig, or by
> supplying a configuration fragment? (A proc file interface would be even
> better, but it's probably not worth going to that much trouble.)
>
> Meanwhile, what kernel source file contains this stuff, so I can hack mine
> today?
>
> --
>
> Ciao,               Paul D. DeRocco
> Paul                mailto:[hidden email]
>
>
> ------------------------------------------------------------------------------
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Re: Real Time Clock

Akram Hameed
Since the possible values for the charging rate is basically a simple ENUM, I think Paul's suggestion is a good one (kconfig item)


On Fri, Aug 9, 2013 at 5:09 AM, Ash Charles <[hidden email]> wrote:
Hi Paul,

The trickle charging is enabled by CONFIG_RTC_DRV_TWL4030.  In the
Linux source code, the driver can be found in
<linux>/drivers/rtc/rtc-twl.c
(https://github.com/gumstix/linux/blob/omap-3.2/drivers/rtc/rtc-twl.c)

In the probe function, you can see some code along the lines of
        /* enable backup battery charging */
        /* use a conservative 25uA @ 3.1V */
        ret = twl_i2c_write_u8(TWL4030_MODULE_PM_RECEIVER,
                BIT_PM_RECEIVER_BB_CFG_BBCHEN |
                BIT_PM_RECEIVER_BB_CFG_BBSEL_3V1 |
                BIT_PM_RECEIVER_BB_CFG_BBISEL_25UA,
                REG_BB_CFG);

--Ash

On Thu, Aug 8, 2013 at 9:39 AM, Paul D. DeRocco <[hidden email]> wrote:
>> From: Ash Charles [mailto:[hidden email]]
>>
>> For what it's worth, I could bump up the default charge rate for the
>> Gumstix kernels.  Does this cause problems or help anyone out?  IIRC,
>> it is set low just to be safe.
>
> Isn't there some way to make this configurable through menuconfig, or by
> supplying a configuration fragment? (A proc file interface would be even
> better, but it's probably not worth going to that much trouble.)
>
> Meanwhile, what kernel source file contains this stuff, so I can hack mine
> today?
>
> --
>
> Ciao,               Paul D. DeRocco
> Paul                mailto:[hidden email]
>
>
> ------------------------------------------------------------------------------
> Get 100% visibility into Java/.NET code with AppDynamics Lite!
> It's a free troubleshooting tool designed for production.
> Get down to code-level detail for bottlenecks, with <2% overhead.
> Download for free and get started troubleshooting in minutes.
> http://pubads.g.doubleclick.net/gampad/clk?id=48897031&iu=/4140/ostg.clktrk
> _______________________________________________
> gumstix-users mailing list
> [hidden email]
> https://lists.sourceforge.net/lists/listinfo/gumstix-users

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Re: Real Time Clock

Paul D. DeRocco
In reply to this post by Ash Charles
> From: Ash Charles [mailto:[hidden email]]
>
> The trickle charging is enabled by CONFIG_RTC_DRV_TWL4030.  In the
> Linux source code, the driver can be found in
> <linux>/drivers/rtc/rtc-twl.c
> (https://github.com/gumstix/linux/blob/omap-3.2/drivers/rtc/rtc-twl.c)
>
> In the probe function, you can see some code along the lines of
>         /* enable backup battery charging */
>         /* use a conservative 25uA @ 3.1V */
>         ret = twl_i2c_write_u8(TWL4030_MODULE_PM_RECEIVER,
>                 BIT_PM_RECEIVER_BB_CFG_BBCHEN |
>                 BIT_PM_RECEIVER_BB_CFG_BBSEL_3V1 |
>                 BIT_PM_RECEIVER_BB_CFG_BBISEL_25UA,
>                 REG_BB_CFG);

I don't see that module anywhere in my build tree. If it was there, I could
figure out how to patch it, but in my build that functionality is either
never being enabled at all, or it's being enabled by some other module. Any
ideas?

--

Ciao,               Paul D. DeRocco
Paul                mailto:[hidden email]


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Re: Real Time Clock

Ash Charles
Hi Paul,

I'm guessing you are compiling your kernel using Yocto.  This guide
offers some useful hints on modifying the kernel build for Yocto:
http://www.yoctoproject.org/docs/current/kernel-dev/kernel-dev.html

Typically though, if I'm playing around in the kernel, I just
cross-compile the kernel directly (a la
http://gumstix.org/basic-cross-compilation.html ) as I find it faster
for just playing around.

@Akram: I like the suggestion of an enum too.  I'm on vacation for the
next week but I'll take a look at it when I get back.

--Ash


On Fri, Aug 9, 2013 at 1:43 AM, Paul D. DeRocco <[hidden email]> wrote:

>> From: Ash Charles [mailto:[hidden email]]
>>
>> The trickle charging is enabled by CONFIG_RTC_DRV_TWL4030.  In the
>> Linux source code, the driver can be found in
>> <linux>/drivers/rtc/rtc-twl.c
>> (https://github.com/gumstix/linux/blob/omap-3.2/drivers/rtc/rtc-twl.c)
>>
>> In the probe function, you can see some code along the lines of
>>         /* enable backup battery charging */
>>         /* use a conservative 25uA @ 3.1V */
>>         ret = twl_i2c_write_u8(TWL4030_MODULE_PM_RECEIVER,
>>                 BIT_PM_RECEIVER_BB_CFG_BBCHEN |
>>                 BIT_PM_RECEIVER_BB_CFG_BBSEL_3V1 |
>>                 BIT_PM_RECEIVER_BB_CFG_BBISEL_25UA,
>>                 REG_BB_CFG);
>
> I don't see that module anywhere in my build tree. If it was there, I could
> figure out how to patch it, but in my build that functionality is either
> never being enabled at all, or it's being enabled by some other module. Any
> ideas?
>
> --
>
> Ciao,               Paul D. DeRocco
> Paul                mailto:[hidden email]
>
>
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Re: Real Time Clock

jzawodn
In reply to this post by Jonathan Kunkee
I'm curious about this as well: what voltage range will the Overo's RTC accept safely?

We have an application that's going to use 4 Overo COMs on a custom board that will be powered off for possibly a few months before it is deployed on the International Space Station.  I'd like to set the clocks on the ground before handing them over to be integrated into the payload and vibration tested, etc.

So I'm wondering if a 500mah LiPo cell (~3.7volt) would do the job.  It should have enough power to run 4 Over RTCs for a long time, but I'm not sure if handing them 3.7 volts will work or not.

Ideas?

Jeremy


On Mon, Aug 5, 2013 at 10:03 PM, Jonathan Kunkee <[hidden email]> wrote:
I haven't dealt with the RTCs on Gumstixen, so I'm curious:

What voltage does the RTC expect?
What's the forward drop of your charger-blocking diode? (It sounds like a low-enough current application that a GaAs or germanium diode would work fine, with their lower forward voltages.)
Have you measured the peak current consumption of the not-otherwise-powered RTC? What is the I-V curve of the battery like? (L-Ions are usually able to keep a steady voltage over a wide range of peak loads, but I'm used to bigger ones.)

If the questions are good food for thought, I'm glad; if the information gets shared here, all the better.

Good luck,
Jon Kunkee


On Mon, Aug 5, 2013 at 10:33 PM, Michael Wynne <[hidden email]> wrote:

I have seen this with the AirSTORM. I tried using some rechargeable 123A lithium cells thinking they would last for long periods of being powered off, but they didn't. Then I tried a regular lithium 2032 button cell and those were dead in a matter of several days. I thought they might heat up and explode because there does seem to be voltage at the RTC Vbackup, though the current must be extremely small because they didn't even get warm. That might explain why the relatively large lithium cells didn't really charge.

Since then I've moved to the recommended Lithium Vanadium Pentoxide rechargeable battery (http://wiki.gumstix.org/index.php?title=Coin_cell). It's very small, but seems to last as long as the others I've tried. Though I haven't conducted extensive testing yet. I have 10 units with this battery and I think I've only seen one go dead and loose the time after being powered off for about 3-4 days. The bottom line is these batteries should be lasting longer. I can leave a desktop PC unplugged for a month and a small battery will keep the RTC going, so what's the deal with these COM's?

At this point I have other projects to worry about, but I intend to investigate further when I can. If anyone can offer any other suggestions I would also be grateful.

-michael

On Aug 5, 2013 5:31 PM, "Nye, Philip" <[hidden email]> wrote:
I am getting reports of the system clock on the Gumstix (overo earth storm) losing big jumps of time - hours or days. This is most likely happening during power cycles though I have not been able to catch it happening. The overo is on our own board which has a non-rechargeable 3V lithium coin cell backing up the RTC.

Does anyone else have experience of anything like this? or pointers to what might be happening?

Is there anything in the backup battery circuitry which could cause the backup battery to drain at an abnormal rate? I know the circuit will trickle-charge a rechargeable cell and ours has a series diode to prevent unwanted back current.

Philip


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Re: Real Time Clock

Chris Cotton
The Gumstix uses a TPS65950 power management IC, which takes care of the RTC backup battery.  According to the datasheet, the maximum recommended voltage for the backup battery supply is 3.3V.  Also, the maximum charge rate of the backup battery circuit built into the TPS65950 is only 1mA.  Therefore you could not simply connect the battery you selected to the VBACKUP pin.

To use the battery you suggested, you would have to use a separate circuit to recharge your LiPo cell, and incorporate a suitable voltage regulator between the battery and the VBACKUP pin on the gumstix to reduce the battery voltage to a safe level.  We have done something similar on one of our designs, in order to run the RTC from the main battery when the unit is switched off.
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