12. ACPI Embedded Controller Interface Specification¶
ACPI defines a standard hardware and software communications interface between an OS driver and an embedded controller. This allows any OS to provide a standard driver that can directly communicate with an embedded controller in the system, thus allowing other drivers within the system to communicate with and use the resources of system embedded controllers. This in turn enables the OEM to provide platform features that the OS OSPM and applications can take advantage of.
ACPI also defines a standard hardware and software communications interface between an OS driver and an Embedded Controller-based SMB-HC (EC-SMB-HC).
The ACPI standard supports multiple embedded controllers in a system, each with its own resources. Each embedded controller has a flat byte-addressable I/O space, currently defined as 256 bytes. Features implemented in the embedded controller have an event “query” mechanism that allows feature hardware implemented by the embedded controller to gain the attention of an OS driver or ASL/AML code handler. The interface has been specified to work on the most popular embedded controllers on the market today, only requiring changes in the way the embedded controller is “wired” to the host interface.
Two interfaces are specified:
A private interface, exclusively owned by the embedded controller driver.
A shared interface, used by the embedded controller driver and some other driver.
This interface is separate from the traditional PC keyboard controller. Some OEMs might choose to implement the ACPI Embedded Controller Interface (ECI) within the same embedded controller as the keyboard controller function, but the ECI requires its own unique host resources (interrupt event and access registers).
This interface does support sharing the ECI with an inter-environment interface (such as SMI) and relies on the ACPI-defined “Global Lock” protocol. Note, however, that HW-reduced ACPI platforms, which do not support the Global Lock, cannot share the EC interface. For information about the Global Lock interface, see Section 6.5.7.
Both the shared and private EC interfaces are described in the following sections.
The ECI has been designed such that a platform can use it in either the legacy or ACPI modes with minimal changes between the two operating environments. This is to encourage standardization for this interface to enable faster development of platforms as well as opening up features within these controllers to higher levels of software.
- 12.1. Embedded Controller Interface Description
- 12.2. Embedded Controller Register Descriptions
- 12.3. Embedded Controller Command Set
- 12.4. SMBus Host Controller Notification Header (Optional), OS_SMB_EVT
- 12.5. Embedded Controller Firmware
- 12.6. Interrupt Model
- 12.7. Embedded Controller Interfacing Algorithms
- 12.8. Embedded Controller Description Information
- 12.9. SMBus Host Controller Interface via Embedded Controller
- 12.10. SMBus Devices
- 12.11. Defining an Embedded Controller Device in ACPI Namespace
- 12.12. Defining an EC SMBus Host Controller in ACPI Namespace