[Gta04-owner] stop boot attempts with flat battery while charging

NeilBrown neilb at suse.de
Sat Feb 16 22:00:52 CET 2013

On Sat, 16 Feb 2013 20:20:24 +0100 "Dr. H. Nikolaus Schaller"
<hns at goldelico.com> wrote:

> Am 16.02.2013 um 19:42 schrieb arne anka:
> > after only a fortnight on the shelf with a full battery, battery was flat again (new one, came with my GTA04 order).
> > i put it on externbal charger and as expected, aftera while it attempted to boot -- from SD, which fails sooner or later in the process.
> > i have my doubt about the healthiness of this constantly failing access to the SD card -- after all, it amounts to probably more than 10 attempts, if not more until at least sufficient charge is available.
> > and every attempt apprently drains the battery again a bit.
> Maybe you should try with NO SD card installed (provided the LXDE in NAND is ok).
> This has two effects:
> 1. it uses the 2.6.32 kernel which appears to me to be a little more stable in this situation
> 2. it saves the power the SD card uses - which may be some 100 mA (depending on size and brand)
> In my experience it typically takes 2-3 attempts until it boots through to LXDE.
> > the only way so far has been to keep the AUX button pressed several minutes until the next boot is attempted (since there's no chance to actually see when it will happen), then switch to NAND which apparently needs much less power and thus succeeds.
> Yes. You can simply boot w/o SD card...
> One more observation is about power management: I have seen that (depending on user space configuration) a 3.7 kernel may switch on Bluetooth and/or WLAN automagically (this is something the 2.6.32 kernel can't do). This may increase power consumption by 200-250 mA at a quite early moment of the boot process. With WLAN/Bluetooth enabled, a 500mA power supply may not be enough to really charge.
> > 
> > so:
> > - is there a way/are there plans to implement a way to prevent booting unless a level of power is reached that actually allows a complete boot?
> Unfortunately we do not know how to implement that. Powering on is attempted by the TPS65950 if battery voltage reaches 3.2V through trickle charge.
> And then only the X-Loader starts. We had tried to add preliminary charging control to X-Loader but that failed (you can only poke some bytes into the control registers).
> The key problem is battery protection and power management (e.g. if the device is connected to a PC). Without running the full USB stack the PC may limit the total charging current to 100 mA without violating the USB specs.
> > - is it possible/planned to somehow prevent booting at all when on charger? that is, booting absolutely and only when pushing the PWR button?
> That can't be implemented at all because active charging must be controlled to some extent.

If I we to try to address this (which I don't really think is a big issue,
but might be nice to fix anyway), I would look at getting u-boot to help out.
All it would need to do is measure the battery status via HDQ, and the status
of the USB ID pin via the PMIC.

If ID pin is grounded, switch battery charger to full current.
If the battery charge is below (say) 2%, power off immediately.

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