[Pkg-acpi-devel] Bug#502511: acpi: Definitely mWh.

[Paul Martin]

Package: acpi
Version: 1.2-1
Followup-For: Bug #502511

# cat /proc/acpi/battery/BAT0/state
present:                 yes
capacity state:          ok
charging state:          charging
present rate:            15682 mW
remaining capacity:      30560 mWh
present voltage:         12378 mV
# cat /proc/acpi/battery/BAT0/info
present:                 yes
design capacity:         47510 mWh
last full capacity:      36160 mWh
battery technology:      rechargeable
design voltage:          10800 mV
design capacity warning: 1808 mWh
design capacity low:     200 mWh
capacity granularity 1:  1 mWh
capacity granularity 2:  1 mWh
model number:            IBM-92P1060
serial number:            1371
battery type:            LION
OEM info:                Panasonic


root at thinkpad:/sys/class/power_supply/BAT0# cat status
Charging
root at thinkpad:/sys/class/power_supply/BAT0# cat energy_now
30670000
root at thinkpad:/sys/class/power_supply/BAT0# cat energy_full
36160000
root at thinkpad:/sys/class/power_supply/BAT0# cat energy_full_design
47510000
root at thinkpad:/sys/class/power_supply/BAT0# cat current_now
1192000
root at thinkpad:/sys/class/power_supply/BAT0# cat voltage_now
12411000


So, energy_* are in µWh and current_now is in µA.

The battery is a nominal capacity of 4400mAh at 10.8V. That's 47.5Wh, 
which corresponds with the "energy_full_design" value.

acpi.c incorrectly considers charge_* and energy_* values to be 
equivalent. charge_* values (if present) will be in µAh, and energy_* 
values (if present) are in µWh.

To convert energy_* values into the equivalent charge_* values, you need 
to divide by (voltage_now/1000000), avoiding overflows or underflows in 
the integer arithmetic.

eg. charge_value = (energy_value / (voltage_now/1000) ) *1000;


Note that 2.6.28-rc7 has the following patch, which triggers this:

commit 558073dd56707864f09d563b64e7c37c021e89d2
Author: Alexey Starikovskiy <aystarik at gmail.com>
Date:   Fri Nov 21 22:41:01 2008 +0800

    ACPI: battery: Convert discharge energy rate to current properly

    ACPI battery interface reports its state either in mW or in mA, and
    discharge rate in your case is reported in mW. power_supply interface
    does not have such a parameter, so current_now parameter is used
    for all cases. But in case of mW, reported discharge should
    be converted into mA.

    Signed-off-by: Alexey Starikovskiy <astarikovskiy at suse.de>
    Tested-by: Ferenc Wagner <wferi at niif.hu>
    Signed-off-by: Len Brown <len.brown at intel.com>


hal has a similar bug. powertop does not.

In addition, "acpi -p" fails because the string "present_rate" should be 
"present rate":

                        } else if (!strcasecmp(value->attr, "present_rate")) {
                                present_rate = get_unit_value(value->value);


-- System Information:
Debian Release: lenny/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'testing'), (500, 'stable'), (99, 'experimental')
Architecture: i386 (i686)

Kernel: Linux 2.6.28-rc7
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash

Versions of packages acpi depends on:
ii  libc6                         2.7-16     GNU C Library: Shared libraries

acpi recommends no packages.

acpi suggests no packages.

-- no debconf information