Yves-Alexis Perez wrote:
Hi,
Evgeni Golov (CC:ed) is currently taking care of fixing acpitool wrt.
sysfs support (which is badly broken).
Using the files in /sys/class/power_supply/BAT*/ we have some wondering
about units.
For the current rate, for example, we have:
corsac@hidalgo: grep . /sys/class/power_supply/BAT0/*now
/sys/class/power_supply/BAT0/current_now:14415000
/sys/class/power_supply/BAT0/energy_now:44170000
/sys/class/power_supply/BAT0/voltage_now:12481000
corsac@hidalgo: grep . /sys/devices/platform/smapi/BAT0/*now
/sys/devices/platform/smapi/BAT0/current_now:1151
/sys/devices/platform/smapi/BAT0/power_now:14365
I'm a bit puzzled with the differences in current_now (the battery is
charging at that time), and don't really know if we can trust the units.
I would assume (in /sys/class/power_supply):
current_now to be in uA
energy_now to be in uWh
voltage_now to be in uV
as said in include/linux/power_supply.h
/*
* All voltages, currents, charges, energies, time and temperatures in uV,
* µA, µAh, µWh, seconds and tenths of degree Celsius unless otherwise
* stated. It's driver's job to convert its raw values to units in which
* this class operates.
*/
and the current (dis)charging rate in W to be
(current_now/1.000.000)*(energy_now/1.000.000). But that gives, for an
end of charge, a charging rate of:
Currently, sysfs interface repeats brokenness of /proc/acpi/battery
interface.
it is possible to have battery info in energy units and charge units.
If you see 'energy_now' variable, then 'current_now' and more
appropriate 'power_now'
will report in uW units.
But if you have 'charge_now', then 'current_now' will report in uA
units, and you will not see 'power_now'.
So, in short, 'charge_now' reports in same units (sans *h) as capacity,
either 'charge_now' or 'energy_now'.
The proper way to handle it is to check for 'energy_now' and if it is
present, look for 'power_now'. It should be
present in 2.6.30 and later kernels (remaining time
energy_now/power_now). If it is not present (as in 2.6.29), then you
should assume that 'current_now' has value in uW, and remaining time is
energy_now/current_now.
If you have 'charge_now', remaining time is charge_now/current_now
without any complications.
Regards,
Alex.
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