Wouter Verhelst <wou...@debian.org> writes:
> On Fri, Apr 24, 2015 at 10:07:36PM +0200, Marco d'Itri wrote:
>> > I'm not sure, if the "acpi" command line utility is that useful which
>> > would warrant having it installed by default. The attached patch drops
>> > it as well. Incidentally, this was also suggested for the laptop-task,
>> > which still pulls it in.
>> The acpi package is *totally useless* and should be immediately dropped
>> from hw-detect and task-laptop.
>
> Disagree.
>
> - Acpi is a useful command-line tool to easily read values of things
> like battery life expectancy and other ACPI power-related values,
> without having to dig through files in /sys.
I'd have to disagree after trying it out just now.
For command like usage I am used to looking at the sysfs files, doing
something like
bjorn@nemi:~$ grep .
/sys/class/power_supply/BAT0/{energy_,voltage_,power_,alarm}*
/sys/class/power_supply/BAT0/energy_full:39480000
/sys/class/power_supply/BAT0/energy_full_design:43200000
/sys/class/power_supply/BAT0/energy_now:38980000
/sys/class/power_supply/BAT0/voltage_min_design:10800000
/sys/class/power_supply/BAT0/voltage_now:12455000
/sys/class/power_supply/BAT0/power_now:0
/sys/class/power_supply/BAT0/alarm:1964000
which gives me a nice overview over the battery status. Note that the
design values (both capacity and voltage) match the DMI data from the
battery:
nemi:/tmp# dmidecode -t 22
# dmidecode 2.12
SMBIOS 2.4 present.
Handle 0x0034, DMI type 22, 26 bytes
Portable Battery
Location: Rear
Manufacturer: SANYO
Name: 42T4643
Design Capacity: 43200 mWh
Design Voltage: 10800 mV
SBDS Version: 03.01
Maximum Error: Unknown
SBDS Serial Number: 0097
SBDS Manufacture Date: 2014-03-03
SBDS Chemistry: LION
OEM-specific Information: 0x00000000
I agree that acpi would have been a useful tool if it provided the same
(or equivalent) information without having to know which sysfs
attributes to look at. But it doesn't. The view it presents is
confusing and plain wrong:
bjorn@nemi:~$ acpi -i -b
Battery 0: Unknown, 98%
Battery 0: design capacity 3468 mAh, last full capacity 3169 mAh = 91%
So what happened to the capacities presented by the battery firmware?
Looks like they were "converted" from their native µWh values to mAh,
apparently using the current voltage for the conversion. Anyone
remotely familiar with battery charging will see the problem... The
rest can study the numbers after unplugging AC (repeated a number of
times with a second or two between to help illustrate the point):
bjorn@nemi:~$ acpi -i -b
Battery 0: Discharging, 98%, discharging at zero rate - will never fully
discharge.
Battery 0: design capacity 3468 mAh, last full capacity 3169 mAh = 91%
bjorn@nemi:~$ acpi -i -b
Battery 0: Discharging, 98%, 03:00:13 remaining
Battery 0: design capacity 3509 mAh, last full capacity 3206 mAh = 91%
bjorn@nemi:~$ acpi -i -b
Battery 0: Discharging, 98%, 02:41:10 remaining
Battery 0: design capacity 3523 mAh, last full capacity 3219 mAh = 91%
bjorn@nemi:~$ acpi -i -b
Battery 0: Discharging, 98%, 02:33:16 remaining
Battery 0: design capacity 3530 mAh, last full capacity 3226 mAh = 91%
bjorn@nemi:~$ acpi -i -b
Battery 0: Discharging, 98%, 02:32:43 remaining
Battery 0: design capacity 3524 mAh, last full capacity 3221 mAh = 91%
So why do both capacities *increase* after unplugging AC? You would
expect them to be stable. The problem is of course that the voltage
decreases. And it will continue to do so, although not at the alarming
rate we see here, until AC power is plugged in again.
Where does this leave acpi? Lying. The battery design capacity was
never 3468, 3509, 3523, 3530 or 3524 mAh. It is 43200 mWh. No need to
mess with that.
acpi does indeed look like a useless tool, not even usable by the few of
us wanting to look at this stuff from the command line.
Bjørn
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