NAME

apm — Advanced Power Management pseudo-device driver

SYNOPSIS

apm0 at mainbus0
#include <machine/apmvar.h> /dev/apm

DESCRIPTION

The apm driver provides support for the Advanced Power Management features of some i386 system BIOSes. The driver supports the Advanced Power Management (APM) BIOS Interface Specification (revision 1.2), published jointly by the Intel Corporation and the Microsoft Corporation.

The APM driver's behavior may be adjusted by specifying any of the following kernel configuration options:

APM_NO_IDLE

Do not call the BIOS CPU idle function from the system idle loop. (Some systems will hang on certain device accesses, such as sound cards or floppy diskette drives, without this option)

APM_V10_ONLY

Use only the APM revision 1.0 specification calls. (Some systems do not implement APM v1.1 very well, and generate weird events instead of the expected events when the system suspend key is pressed.)

APM_NO_V12

Don't attach to the BIOS as APM v1.2 compliant device. (In case there are problems with v1.2 support.)

APM_NO_STANDBY

Do not attempt to put the system into standby mode.

APM_NO_POWEROFF

Do not attempt to turn off power when halting the system.

APM_FORCE_64K_SEGMENTS

Force the length of the APM BIOS code and data segments to 64KB.

APM_ALLOW_BOGUS_SEGMENTS

Allow the use of data segments which are in unexpected locations.

APMDEBUG

Enable kernel printout of events received from the APM BIOS.

APMCALLDEBUG

Enable kernel printout of every call to the APM BIOS (this is very noisy).

APM_POWER_PRINT

Print power state on console at APM_POWER_CHANGE events. (Since it increases syslogd(8)'s activity, it may consume increased battery power. Some systems generate the events too frequently, and printing the status may disturb single-user operations.)

APM_DISABLE_INTERRUPTS

Set this to zero if you don't want the kernel to disable interrupts before calling the BIOS. This is required for most IBM ThinkPads, and some other newer laptops. A good indication that you need this is that the machine hangs just after resuming from suspended state. It's unclear if doing this has negative effects on older BIOS, therefore it defaults to one (i.e interrupts are disabled).

If no processes are holding open file descriptors to the APM device, the driver will process the APM BIOS events itself. If a process has the device open for write, the driver defers all suspend and standby processing to the user process as long as there is sufficient queue space to store the event for the process. If the device is only open for read, the driver will report events but handle them itself.

The APM device may be opened by multiple readers but only one writer. Multiple readers may fetch the status with ioctl(2) without worrying about interference, but they must cooperate to share events as only a single event queue is provided. The device may only be select(2)ed or manipulated with ioctl(2); read(2) and write(2) are not supported. The ioctl(2) calls supported are:

APM_IOC_SUSPEND

Initiate an APM suspend mode. This is a deep sleep mode which powers down most devices. The device must be open for writing for this command to succeed.

APM_IOC_STANDBY

Initiate an APM standby mode. This is a light sleep mode from which the system can quickly restore normal operation. The device must be open for writing for this command to succeed.

APM_IOC_GETPOWER

Fetch the current power status into an apm_power_info structure.

struct apm_power_info { 
	u_char battery_state; 
	u_char ac_state; 
	u_char battery_life; 
	u_char spare1; 
	u_int minutes_left;		/* estimate */ 
	u_int nbattery; 
	u_int batteryid; 
	u_int spare2[4]; 
};

The structure should be zeroed (except for batteryid) before being passed.

battery_state is one of APM_BATT_HIGH, APM_BATT_LOW, APM_BATT_CRITICAL, APM_BATT_CHARGING, or APM_BATT_UNKNOWN.

ac_state is one of APM_AC_OFF, APM_AC_ON, APM_AC_BACKUP, or APM_AC_UNKNOWN.

battery_life is the percentage estimated remaining normal battery life (or 0 if the BIOS cannot provide an estimate).

minutes_left is an estimated remaining lifetime (or 0 if the BIOS cannot provide an estimate).

nbattery is the number of batteries in the system. If the system is using APM v1.1 or earlier, nbattery will always return 0.

Batteries are numbered from a base of 1. If the passed value of batteryid is 0, the returned values will reflect the percentage remaining, minutes left, etc. of all of the system's batteries taken together. If the passed value of batteryid is nonzero, the return values will reflect the indicated battery's percentage remaining, minutes left, etc. It is an error to set batteryid to a value greater than that returned by nbattery. If the system is using APM v1.1 or earlier, individual batteries cannot be queried, and nbattery will always return 0. batteryid is always set to the passed value upon return.

APM_IOC_NEXTEVENT

Fetch the next event from the APM BIOS into an apm_event_info structure. If no more events are ready, this will return EAGAIN.

struct apm_event_info { 
      u_int type; 
      u_int index; 
      u_int spare[8]; 
};

type is one of the APM event types (APM_STANDBY_REQ through APM_SYS_STANDBY_RESUME). index is the ordinal event sequence number.

SEE ALSO

apmd(8)

REFERENCES

Advanced Power Management (APM) BIOS Interface Specification (Revision 1.1), Intel Corporation and Microsoft Corporation. Intel order number 241704-001; Microsoft part number 781-110-X01.

HISTORY

The apm pseudo-device driver appeared in NetBSD 1.3.