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9. Advanced Power Management (APM)

The Libretto 70 has BIOS support for APM 1.1, but you must enable it in the BIOS setup (accessible by pressing and holding the Esc key while booting, then pressing F1 when prompted to do so), or within Toshiba's Power Saver application (accessible from the Windows 95 Control Panel).

APM support is included in the kernel if you have followed the instructions above. The relevant settings in /usr/src/linux/.config are:

CONFIG_APM=y
# CONFIG_APM_IGNORE_USER_SUSPEND is not set
CONFIG_APM_DO_ENABLE=y
CONFIG_APM_CPU_IDLE=y
# CONFIG_APM_DISPLAY_BLANK is not set
CONFIG_APM_POWER_OFF=y

The Libretto has a particularly nice feature referred to by Toshiba as ``hibernation mode'', which (if properly configured) allows you to suspend the Libretto simply by folding the display panel down over the keyboard. I used Toshiba's Power Saver application to set my Libretto to suspend when the panel is closed, and to shut off after 10 minutes in hibernation if the system is running on battery power. When the Libretto enters hibernation mode, it saves its state (the contents of RAM) in the hidden portion of its internal disk, and then shuts off the disk drive. If the display is reopened within 10 minutes, the contents of RAM are unchanged and the system can be used immediately. After 10 minutes, or if the battery has been changed, the contents of RAM are restored from disk, an operation that takes about 20 seconds.

When resuming operation after the Libretto has been suspended while an X session is in progress, I have occasionally found that the mouse pointer will be frozen for as much as 30 seconds. This seems to occur only if I attempt to move the mouse pointer while RAM is being restored from disk, or within a second or two afterwards. It appears that this problem can be completely avoided simply by not touching the mouse for a few seconds after resuming operation. Another harmless effect occurs when running X in 24-bit color mode: the mouse pointer becomes black (not invisible, just black) after return from hibernation.

The state of the battery can be determined by examining /proc/apm, for example, like this:

cat /proc/apm
1.2 1.1 0x02 0x00 0x01 0x02 47% -1 ?

(In this case, the output, shown on the second line above, indicates that the battery charge is at 47% of capacity.) The estimated time remaining, available from some APM implementations, is apparently not provided by the Libretto. The flag bits indicate if the Libretto is running on battery or external power (experiment to see how this works).

The kernel is configured to attempt to reduce power consumption while idle, and it also supports turning off the Libretto upon a system halt. It is thus possible to use the command

shutdown -h now

to shut down Linux cleanly and turn the system power off. In combination with wakeup mode (accessible from the Windows 95 Power Saver application, or from the BIOS setup), the Libretto can thus be made to turn itself on at a scheduled time, perform some task, and then turn itself off again. (To access the BIOS setup, hold down Esc while the Libretto is booting, then press F1 when prompted to do so.)

You may wish to obtain the Linux APM utilities, ftp://ftp.cs.unc.edu/pub/users/faith/linux/apmd-2.4.tar.gz; these include xapm, a tiny X11-based application that displays a battery status indicator in an X-window. Also check out the Battery Powered Linux Mini-HOWTO, http://sunsite.unc.edu/LDP/HOWTO/mini/Battery-Powered.html.


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