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DESCRIPTION

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 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.