12.11. Defining an Embedded Controller Device in ACPI Namespace

An embedded controller device is created using the named device object. The embedded controller’s device object requires the following elements:

Table 12.19 Embedded Controller Device Object Control Methods

Object	Description
_CRS	Named object that returns the Embedded Controller’s current resource settings. Embedded Controllers are considered static resources; hence only return their defined resources. The embedded controller resides only in system I/O or memory space. The first address region returned is the data port, and the second address region returned is the status/command port for the embedded controller. If the EC is used on a HW-Reduced ACPI platform, a third resource is required, which is the GPIO Interrupt Connection resource for the EC’s SCI Interrupt. CRS is a standard device configuration control method defined in _CRS (Current Resource Settings).
_HID	Named object that provides the Embedded Controller’s Plug and Play identifier. This value is set to PNP0C09. _HID is a standard device configuration control method defined in _HID (Hardware ID).
_GPE	Named Object that evaluates to either an integer or a package. If _GPE evaluates to an integer, the value is the bit assignment of the SCI interrupt within the GPEx_STS register of a GPE block described in the FADT that the embedded controller will trigger. If _GPE evaluates to a package, then that package contains two elements. The first is an object reference to the GPE Block device that contains the GPE register that will be triggered by the embedded controller. The second element is numeric (integer) that specifies the bit assignment of the SCI interrupt within the GPEx_STS register of the GPE Block device referenced by the first element in the package. This control method is specific to the embedded controller. This method is not required on Hardware-reduced ACPI platforms.

12.11.1. Example: EC Definition ASL Code

Example ASL code that defines an embedded controller device is shown below:

Device(EC0) {
                                        // PnP ID
    Name(_HID, EISAID("PNP0C09"))
                                        // Returns the "Current Resources" of EC
    Name(_CRS,
        ResourceTemplate(){ // port 0x62 and 0x66
            IO(Decode16, 0x62, 0x62, 0, 1),
            IO(Decode16, 0x66, 0x66, 0, 1)
        /* For HW-Reduced ACPI Platforms, include a GPIO Interrupt Connection resource,
            e.g. GPIO controller #2, pin 43.
            GpioInt(Edge, ActiveHigh, ExclusiveAndWake,PullUp 0, "\\_SB.GPI2"){43}
        */
            }
        )
                                        // Define that the EC SCI is bit 0 of the GP_STS register
        Name(_GPE, 0)                   // Not required for HW-Reduced ACPI platforms
        OperationRegion(ECOR, EmbeddedControl, 0, 0xFF)
        Field(ECOR, ByteAcc, Lock, Preserve) {
                                        // Field definitions go here
            }
        }