ACPIEC(4)               NetBSD 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 Gen-
     eral 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 trig-
     gered 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 interrupt.
     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 processing 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 reasons,
     the initialization of the whole acpi(4) subsystem may be problematic.

NetBSD 6.0                     February 27, 2010                    NetBSD 6.0

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