[Gta04-owner] charging log

NeilBrown neilb at suse.de
Mon Sep 9 01:53:13 CEST 2013


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

  7.4.1.1.3  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.

My logs show the twl4030_usb voltage between 4.81 and 5.18.

Possibly setting a lower charge current (via those udev rules) might allow
the voltage to remain high.

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.

NeilBrown


> 
> Software only turns on the charger if you manually unplug USB and replug
> because only then, you get an MUSB event that enables charging.
> 
> There have been heavy discussions last year that this behaviour is right,
> i.e. that you battery drains even if connected to USB and that we can't
> do anything...
> 
> The main argument is that this is a safety comparator detecting USB
> unplugging even if the CPU isn't. And if the CPU would override that
> (which is easily done - I had discussed and tested a patch), there is a
> risk of overcharging the battery.
> 
> BR,
> Nikolaus
> 

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