Advanced Configuration and Power Interface Specification

ACPI Hardware Specification
OSPM responds to the SCI and calls the AML code event handler associated with that generic event.
The ACPI table associates the hardware event with the AML code event handler.
The AML-code event handler collects the appropriate information and then executes an AML Notify
command to indicate to OSPM that a particular bus needs re-enumeration.
The following sections describe the fixed and generic hardware feature set of ACPI. These sections
enable a reader to understand the following:
• Which hardware registers are required or optional when an ACPI feature, concept or interface is
required by a design guide for a platform class
• How to design fixed hardware features
• How to design generic hardware features
• The ACPI Event Model
4.4 Diagram Legends
The hardware section uses simplified logic diagrams to represent how certain aspects of the
hardware are implemented. The following symbols are used in the logic diagrams to represent
programming bits.
Write-only control bit
Enable, control or status bit
Sticky status bit
##
Query value
The half round symbol with an inverted “V” represents a write-only control bit. This bit has the
behavior that it generates its control function when it is set. Reads to write-only bits are treated as
ignore by software (the bit position is masked off and ignored).
The round symbol with an “X” represents a programming bit. As an enable or control bit, software
setting or clearing this bit will result in the bit being read as set or clear (unless otherwise noted). As
a status bit it directly represents the value of the signal.
The square symbol represents a sticky status bit. A sticky status bit is set by the level (not edge) of a
hardware signal (active high or active low). The bit is only cleared by software writing a “1” to its bit
position.
The rectangular symbol represents a query value from the embedded controller. This is the value the
embedded controller returns to the system software upon a query command in response to an SCI
event. The query value is associated with the event control method that is scheduled to execute upon
an embedded controller event.
4.5 Register Bit Notation
Throughout this section there are logic diagrams that reference bits within registers. These diagrams
use a notation that easily references the register name and bit position. The notation is as follows:
Registername.Bit
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