[Gta04-owner] charging log

[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
> 
>   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.

Yes it seems to help.

root at neo:/sys/devices/platform/omap_i2c.1/i2c-1/1-004b/twl4030_bci# cat 
/sys/class/power_supply/twl4030_usb/uevent
POWER_SUPPLY_NAME=twl4030_usb
POWER_SUPPLY_STATUS=Charging
POWER_SUPPLY_ONLINE=1
POWER_SUPPLY_VOLTAGE_NOW=4475322
POWER_SUPPLY_CURRENT_NOW=507690

root at neo:/sys/devices/platform/omap_i2c.1/i2c-1/1-004b/twl4030_bci# echo 
250000 > max_current 

root at neo:/sys/devices/platform/omap_i2c.1/i2c-1/1-004b/twl4030_bci# cat 
/sys/class/power_supply/twl4030_usb/uevent
POWER_SUPPLY_NAME=twl4030_usb
POWER_SUPPLY_STATUS=Charging
POWER_SUPPLY_ONLINE=1
POWER_SUPPLY_VOLTAGE_NOW=4810629
POWER_SUPPLY_CURRENT_NOW=256758


I didnt know that changing max_current on the fly is possible. Now we could 
implement quite clever charging. E.g. slowly raising max_current from 100 and 
checking if voltage is safely above 4.5V. We could also lower max_current when 
the battery is nearly full and try to keep battery's current_now at 0 so that 
it charges very very slowly. Does this sound good?

Regards

Radek




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