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ACPI_BATTERY(4) Device Drivers Manual ACPI_BATTERY(4)

acpi_battery — ACPI battery management subsystem

device acpi

The acpi_battery is a driver for battery management features of the ACPI module.

An ACPI-compatible battery device supports either a Control Method Battery interface or a Smart Battery subsystem interface. The former is accessed by the AML (ACPI Machine Language) code control methods, and the latter is controlled directly through the ACPI EC (Embedded Controller) typically via an SMBus interface.

This driver supports the sysctl(8) and ioctl(2) interfaces as well as the devd(8) event notification interface.

Every ioctl for the acpi_battery driver takes a single integer value for the battery unit number as an argument, and returns a specific structure for each request. A special unit number ACPI_BATTERY_ALL_UNITS specifies all of the attached units and reports accumulated information.

int
Returns the number of battery units in the system. The unit number argument will be ignored.
struct acpi_battinfo
Returns the following:
cap
Battery capacity in percent,
min
Remaining battery life in minutes,
state
Current status of the battery encoded in the following:
(0x0001)
Battery is discharging,
(0x0002)
Battery is being charged, or
(0x0004)
Remaining battery life is critically low.

Note that the status bits of each battery will be consolidated when ACPI_BATTERY_ALL_UNITS is specified.

rate
Current battery discharging rate in mW. -1 means not discharging right now.
struct acpi_bix
Returns battery information given by the ACPI _BIX (Battery Information) object, which is the static portion of the Control Method Battery information. In the case of a Smart Battery attached to SMBus or a Control Method Battery with a _BIF object, this ioctl will build a struct acpi_bix structure based on the obtained information and return it.
rev
Revision number of the object. There are the following well-known values:
(0x0000)
A _BIX object in ACPI 4.0.
(0x0001)
A _BIX object in ACPI 6.0.
(0xffff)
A _BIX object built from the _BIF object found on the system.

Note that this field should be checked by using (var, rev) macro when checking the minimum revision number.

units
Indicates the units used by the battery to report its capacity and charge rate encoded in the following:
ACPI_BIX_UNITS_MW (0x00000000)
in mW (power)
ACPI_BIX_UNITS_MA (0x00000001)
in mA (current)

Note that capacity is expressed in mWh or mAh, and rate is expressed in mW or mA, respectively.

dcap
The Battery's design capacity, which is the nominal capacity of a new battery. This is expressed as power or current depending on the value of units.
lfcap
Predicted battery capacity when fully charged. Typically this will decrease every charging cycle.
btech
Battery technology:
0x00000000 Primary cell (non-rechargable)
 
0x00000001 Secondary cell (rechargable)
 
dvol
Design voltage in mV, which is the nominal voltage of a new battery.
wcap
Design capacity of warning. When a discharging battery device reaches this capacity, notification is sent to the system.
lcap
Design capacity of low.
cycles
(rev 0 or newer) The number of cycles the battery has experienced. A cycle means an amount of discharge occurred which was approximately equal to the value of Design Capacity.
accuracy
(rev 0 or newer) The accuracy of the battery capacity measurement, in thousandth of a percent.
stmax
(rev 0 or newer) The Maximum Sampling Time of the battery in milliseconds. This is the maximum duration between two consecutive measurements of the battery's capacities specified in _BST. If two succeeding readings of _BST beyond this duration occur, two different results can be returned.
stmin
(rev 0 or newer) The Minimum Sampling Time of the battery in milliseconds.
aimax
(rev 0 or newer) The Maximum Average Interval of the battery in milliseconds. This is the length of time within which the battery averages the capacity measurements specified in _BST. The Sampling Time specifies the frequency of measurements, and the Average Interval specifies the width of the time window of every measurement.
aimin
(rev 0 or newer) The Minimum Average Interval of the battery in milliseconds.
gra1
Battery capacity granularity between low and warning. This is expressed as power or current depending on the value of units.
gra2
Battery capacity granularity between warning and full. This is expressed as power or current depending on the value of units.
model
Model number of the battery as a string.
serial
Serial number of the battery as a string.
type
Type identifier of the battery as a string.
oeminfo
OEM-specific information of the battery as a string.
scap
(rev 1 or newer) Battery swapping capability encoded in the following:
ACPI_BIX_SCAP_NO (0x00000000)
Non-swappable
ACPI_BIX_SCAP_COLD (0x00000001)
Cold-swappable
ACPI_BIX_SCAP_HOT (0x00000010)
Hot-swappable
struct acpi_bif
(deprecated) Returns battery information given by the ACPI _BIF (Battery Information) object, which was deprecated in ACPI 4.0 specification. The data structure is a subset of struct acpi_bix.

Note that this ioctl will built a struct acpi_bif structure based on the obtained information even if this object is not available and a _BIX object is found.

ACPIIO_BATT_GET_BST struct acpi_bst
Returns battery information given by the ACPI _BST (Battery Status) object, which is the present battery status. In the case of a Smart Battery attached to SMBus, this ioctl will build a struct acpi_bst structure based on the obtained information and return it.
state
Battery state. The value is encoded in the same way as state of struct acpi_battinfo.
rate
Battery present rate of charging or discharging. The unit of the value depends on unit of struct acpi_bif.
cap
Battery remaining capacity. The unit of this value depends on unit of struct acpi_bif.
volt
Battery present voltage.

The following sysctl(8) variables export battery status. Note that they are accumulated status of all of the connected batteries:

hw.acpi.battery.info_expire
Information cache expiration time in seconds. The battery information obtained by _BIX or _BIF object will be stored and reused for successive read access to this MIB within the specified period.
hw.acpi.battery.units
Number of battery units in the system.
hw.acpi.battery.state
Current battery charging status. This is same as state of struct acpi_battinfo.
hw.acpi.battery.rate
Current battery discharging rate in mW.
hw.acpi.battery.time
Remaining battery life in minutes. If the battery is not discharging, the value shows -1.
hw.acpi.battery.life
Battery capacity in percent.

Battery-related event notifications are sent to the userland via the devd(8) interface. See /etc/devd.conf and devd.conf(5) for more details. Note that notifications are supported only by the Control Method Battery.

The acpi_battery driver sends events with the following attributes:

system
subsystem
type
The fully qualified battery object path as in the ASL.
notify
An integer designating the event:

Battery status was changed.
Battery information was changed.

acpi(4), acpiconf(8)

Nate Lawson <njl@FreeBSD.org>, Munehiro Matsuda, Takanori Watanabe <takawata@FreeBSD.org>, Mitsuru IWASAKI <iwasaki@FreeBSD.org>, Hans Petter Selasky <hselasky@FreeBSD.org>, and Hiroki Sato <hrs@FreeBSD.org>.

This manual page was written by Takanori Watanabe <takawata@FreeBSD.org> and Hiroki Sato <hrs@FreeBSD.org>.

February 16, 2020 Debian