Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
5. The OS looks to see what _EJx control methods are present for the device. If the removal event
will cause the system to switch to battery power (in other words, an undock) and the battery is
low, dead, or not present, OSPM uses the lowest supported sleep state _EJx listed; otherwise it
uses the highest state _EJx. Having made this decision, OSPM runs the appropriate _EJx control
method to prepare the hardware for eject.
6. Warm removal requires that the system be put in a sleep state. If the removal will be a warm
removal, OSPM puts the system in the appropriate Sx state. If the removal will be a hot removal,
OSPM skips to step 8, below.
7. For warm removal, the system is put in a sleep state. Hardware then uses any motors, and so on,
to eject the device. Immediately after ejection, the hardware transitions the computer to S0. If
the system was sleeping when the eject notification came in, the OS returns the computer to a
sleeping state consistent with the user’s wake settings.
8. OSPM calls _STA to determine if the eject successfully occurred. (In this case, control methods
do not need to use the Notify(device,3) command to tell OSPM of the change in _STA) If there
were any mechanical failures, _STA returns 3: device present and not functioning, and OSPM
informs the user of the problem.
Note: This mechanism is the same for removing a single device and for removing several devices, as in
an undock.
ACPI does not disallow surprise-style removal of devices; however, this type of removal is not
recommended because system and data integrity cannot be guaranteed when a surprise-style removal
occurs. Because the OS is not informed, its device drivers cannot save data buffers and it cannot stop
accesses to the device before the device is removed. To handle surprise-style removal, a generalpurpose
event must be raised. Its associated control method must use the Notify command to
indicate which bus the device was removed from.
The device insertion and removal objects are listed in Table 6-184.
Table 6-184 Device Insertion, Removal, and Status Objects
Object
_EDL
_EJD
_EJx
_LCK
_OST
_RMV
_STA
Description
Object that evaluates to a package of namespace references of device objects that depend on
the device containing _EDL.
Object that evaluates to the name of a device object on which a device depends. Whenever the
named device is ejected, the dependent device must receive an ejection notification.
Control method that ejects a device.
Control method that locks or unlocks a device.
Control method invoked by OSPM to convey processing status to the platform.
Object that indicates that the given device is removable.
Control method that returns a device’s status.
6.3.1 _EDL (Eject Device List)
This object evaluates to a package of namespace references containing the names of device objects
that depend on the device under which the _EDL object is declared. This is primarily used to support
docking stations. Before the device under which the _EDL object is declared may be ejected, OSPM
prepares the devices listed in the _EDL object for physical removal.
332 April, 2015 Version 6.0