Advanced Configuration and Power Interface Specification

Device Configuration
are present, which devices are physically in the same device (independent of which bus the devices
live on), and methods for controlling ejection or interlock mechanisms.
The system is more stable when removable devices have a software-controlled, VCR-style ejection
mechanism instead of a “surprise-style” ejection mechanism. In this system, the eject button for a
device does not immediately remove the device, but simply signals the operating system. OSPM
then shuts down the device, closes open files, unloads the driver, and sends a command to the
hardware to eject the device.
1. If the device is physically inserted while the computer is in the working state (in other words, hot
insertion), the hardware generates a general-purpose event.
2. The control method servicing the event uses the Notify(device,0) command to inform OSPM of
the bus that the new device is on or the device object for the new device. If the Notify command
points to the device object for the new device, the control method must have changed the
device’s status returned by _STA to indicate that the device is now present. The performance of
this process can be optimized by having the object of the Notify as close as possible, in the
namespace hierarchy, to where the new device resides. The Notify command can also be used
from the _WAK control method (for more information about _WAK, see Section 7.4.5 “\_WAK
(System Wake)”) to indicate device changes that may have occurred while the computer was
sleeping. For more information about the Notify command, see Section 5.6.3 “Device Object
Notification.”
3. OSPM uses the identification and configuration objects to identify, configure, and load a device
driver for the new device and any devices found below the device in the hierarchy.
4. If the device has a _LCK control method, OSPM may later run this control method to lock the
device.
The new device referred to in step 2 need not be a single device, but could be a whole tree of devices.
For example, it could point to the PCI-PCI bridge docking connector. OSPM will then load and
configure all devices it found below that bridge. The control method can also point to several
different devices in the hierarchy if the new devices do not all live under the same bus. (in other
words, more than one bus goes through the connector).
For removing devices, ACPI supports both hot removal (system is in the S0 state), and warm
removal (system is in a sleep state: S1-S4). This is done using the _EJx control methods. Devices
that can be ejected include an _EJx control method for each sleeping state the device supports (a
maximum of 2 _EJx objects can be listed). For example, hot removal devices would supply an _EJ0;
warm removal devices would use one of _EJ1-EJ4. These control methods are used to signal the
hardware when an eject is to occur.
The sequence of events for dynamically removing a device goes as follows:
1. The eject button is pressed and generates a general-purpose event. (If the system was in a
sleeping state, it should wake the computer).
2. The control method for the event uses the Notify(device, 3) command to inform OSPM which
specific device the user has requested to eject. Notify does not need to be called for every device
that may be ejected, but for the top-level device. Any child devices in the hierarchy or any
ejection-dependent devices on this device (as described by _EJD, below) are automatically
removed.
3. The OS shuts down and unloads devices that will be removed.
4. If the device has a _LCK control method, OSPM runs this control method to unlock the device.
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