[Gta04-owner] charging log

Dr. H. Nikolaus Schaller hns at goldelico.com
Mon Sep 9 08:19:48 CEST 2013

Am 09.09.2013 um 07:33 schrieb Radek Polak:

> On Monday, September 09, 2013 01:53:13 AM NeilBrown wrote:
> > On Sun, 8 Sep 2013 19:26:55 +0200 "Dr. H. Nikolaus Schaller"
> > 
> > <hns at goldelico.com> wrote:
> > > Essentially it shows that your USB charging voltage is too low. It should
> > > be ~5V. Maybe you are drawing too much current from the charger or
> > > the cable is weak.
> > > 
> > > There is a comparator in the TWL-usb-chager hardware set at fixed
> > > 4.5V that turns off the charger if VBUS goes below.
> > 
> > Actually 4.4V according to my documentation

I didn't look into the doc again and did only remember 4.something.

> > 
> >  VBUS Detection
> >   The VBUS presence comparator, which is part of the precharge analog
> > hardware, detects whether a USB device capable of supplying the VBUS pin
> > is plugged in. When VBUS is detected (VBUS voltage is higher than 4.4 V),
> > a communication between the BCI and the USB detects whether the USB device
> > plugged is a USB host, a carkit, or a USB charger. Fast precharge with
> > charger is not supported.
> > 
> > In Radek's logs the voltage is initially around 4.5 but then drops below
> > 4.4 while charging.  It finished the charge at aout 4.4V but it seems this
> > is too low to restart.

AFAIK it will never restart unless triggered by software. And the only trigger we
have is through MUSB plug-in detection.

> > 
> > My logs show the twl4030_usb voltage between 4.81 and 5.18.

Yes, that its what it should be.

> I tried yesterday with my notebook and very short USB cable and it worked as expected (attached log).
> > Possibly setting a lower charge current (via those udev rules) might allow
> > the voltage to remain high.
> Good idea. I'll try.
> > I've been thinking it would occasionally be useful to be able to turn
> > charging on and off directly via some field in sysfs.
> > You could then at least manually turn it on again.
> I think this could be nice feature.

Yes, indeed! It would be better than unplugging/replugging USB - which could
break a ssh connection...

And what also would be useful is to report the "hardware did shutdown" situation
to user space. Although a clever client can detect the "Not Charging" state and
then query the hwmon for the VBUS and report if it is >4.4V. Or even 4.8V
and report a bad charger.

Patches are welcome for inclusion in the 3.11/12 kernel.


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