Hi.
Hmm I'm getting -EINVAL when I do echo 1600000 > charge_now but yet the
value does get updated?
Hm. I'm getting "Permission denied" when trying to do this.
Anyway, charge_now value is not supposed to be initialized by the user.
Only charge_full should be writable.
And I'm still not seeing capacity show up after that though even with
full battery.. I think we should be able to calculate it if either a
high or
low value has been seen?
There are two steps needed to calibrate the battery: to hit the "fully
charged"
state and to hit "battery empty" state. When the both states were hit the
driver
will initialize charge_full value. And it will start reporting correct
charge_now
and capacity (battery charge percentage) values.
Once the charge_full value is calculated it's recommended to be saved by
the user
to a permanent storage between reboots.
Saving/restoring the value can be done in init scripts.
For saving the calibration value just use the command like:
cat /sys/class/power_supply/battery/charge_full > /battery_cf
To restore (after device reboot or power on):
cat /battery_cf > /sys/class/power_supply/battery/charge_full
This will allow the kernel to do fast calibration. I.e. you will
only need to fully charge _OR_ fully discharge the battery to start
seeing correct charge_now and capacity values.
Also, we should have the driver default to using the charge_full_design
value if nothing is written from userspace and we see a high or low
value.
I'd prefer to have charge_full value undefined until the battery is
calibrated.
This way the userspace can estimate current battery capacity using voltage
as a
fallback for uncalibrated battery. The voltage estimation will be way more
accurate than having charge_full = charge_full_design on pretty old Droid 4
batteries. For example, my battery after calibration has about 1000 mAh,
while charge_full_design is 1740000.
Maybe some pessimistic estimate could be used instead of just using
charge_full_design if no value is initialized from the userspace?
Something like (charge_full_design / 4) * 3 maybe?
It's better to rely on voltage estimated percentage.
In Maemo Leste we patched upower to use the following formula, which gives
pretty
good results:
percentage = (voltage - voltage_empty) / (voltage_full - voltage_empty) *
100
Actually, the formula we use is a bit more complicated.
If you're curious, here's how it's actually done:
https://github.com/maemo-leste/upower/blob/master/src/linux/up-device-supply.c#L756
--
Best regards, Spinal
