Specifications

2.4.2.5 Legacy Interrupt Protocol

The Legacy Interrupt Protocol manages the programming of PCI interrupts. The table

below lists the functions that are included in the Legacy Interrupt Protocol. See

EFI_LEGACY_INTERRUPT_PROTOCOL in Code Definitions for the definitions of these

functions.

Table 7 Functions in Legacy Interrupt Protocol

Functions Description

GetNumberPirqs() Returns the number of PIRQs that the chipset supports.

GetLocation() Returns the PCI bus location of the chipset. The $PIR table requires

this information.

ReadPirq() Reads the current PIRQ contents for the indicated PIRQ.

WritePirq() Writes the current PIRQ contents for the indicated PIRQ.

Compatibility16

The Compatibility16 code is a stripped-down version of a traditional BIOS that removes

the POST and BIOS Setup code. This stripped-down BIOS consists of the following:

• Runtime code

• INT18 code

• INT19 code

• A small piece of new code to handle the interface between EfiCompatibility

code and Compatibility16 code

The design goal is to have the Compatibility16 code be universal for each class of

platforms. Examples are desktop, server, and mobile platforms. This goal implies that

the Compatibility16 code is chipset and platform neutral. It controls hardware through

traditional hardware interfaces and leaves the chipset programming to EFI and/or

EfiCompatibility. This design goal maximizes reusability and minimizes code bugs.

2.4.3.1 Communication between EfiCompatibility and Compatibility16

The communication between EfiCompatibility modules and Compatibility16 occurs using

the following three mechanisms:

• Compatability16 Table

• Compatability16 Functions

• Compatability16 Function Data Structures

The following sections discuss these mechanisms in more detail. See

Compatibility16

Code in Code Definitions for definitions of these functions and structures.