ACPIEC(4)						   BSD Kernel Interfaces Manual 						 ACPIEC(4)

NAME

     acpiec -- ACPI Embedded Controller

SYNOPSIS

     acpiec* at acpi?
     acpiecdt* at acpi?

DESCRIPTION

     The acpiec driver supports ACPI Embedded Controllers.

     An ACPI Embedded Controller (EC) is typically a small microprocessor that is responsible for various tasks related to ACPI.  The primary task
     is to handle ACPI specific interrupts, which are mapped to so-called ACPI General Purpose Events (GPEs).  Other possible functions include
     embedded access to other buses such as the iic(4).

     The ACPI specific events range from user initiated events to events triggered by the hardware.  When such an event occurs, typically either a
     System Management Interrupt (SMI) or a System Control Interrupt (SCI) is raised.  The latter is an active, visible, shareable, level inter-
     rupt.  On most Intel chipsets SCI is hardwired to the interrupt number 9.	The main task of an EC is to raise a system control interrupt.

     All GPEs generate SCIs.  A typical example of the internal wiring of GPEs could involve gpio(4): when, e.g., the AC adapter is connected, a
     certain GPIO line becomes active, a given GPE is flagged, and a SCI interrupt is raised by the EC, leading to execution of ACPI machine code
     in order to locate the handler associated with the event.	A corresponding driver, acpiacad(4) in this case, will finally finish the process-
     ing of the event.

     Due to the reasons described above, majority of ACPI specific drivers are dysfunctional without acpiec.  It is therefore recommended that
     acpiec is always enabled, even though it may not be required on some older systems.

SEE ALSO

     acpi(4)

HISTORY

     The acpiec driver appeared in NetBSD 1.6.

CAVEATS

     Many machines depend on early attachment of acpiec.  In such cases the information required by acpiec should be available as a separate and
     optional Embedded Controller Descriptor Table (ECDT).  If an ECDT is not available or early attachment can not be carried out due other rea-
     sons, the initialization of the whole acpi(4) subsystem may be problematic.

BSD
								 February 27, 2010							       BSD