UEFI与固件程序设计
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同济大学软件学院
What’s the UEFI?
UEFI (Unified Extensible Firmware Interface)是由英特尔公
司联合业界共同提出的一种欲在未来电脑系统中替代传统
BIOS (Legacy BIOS)的升级解决方案。
Another question, What’s the BIOS?
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What’s the BIOS?
BIOS (Basic Input and Output System)基本输入输出系统，它是
一组固化到计算机内主板上一个ROM芯片上的程序，它保存
着计算机最重要的开机上电自检、硬件初始化程序和系统底
层的服务程序等。
Push
Power Button
硬件逻辑
CPU
Reset
Found
MBR
BIOS
OS
RTC
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Agenda
– BIOS background
 History
 Functions
 Legacy
BIOS’s Flaws
 Change
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BIOS background -- History
 Before
firmware— Switchs on a piece of plywood
 BIOS--for
 EFI--
original IBM PC/XT and PC/AT in 1980s
Spring 2000 IDF (Intel Developer’s Forum)
-- EFI 1.10 specification
 UEFI–
Originated from the EFI 1.10 specification
--Updated and managed by the Unified EFI Forum
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BIOS background -- Functions




Based on 8086 architecture
POST—Power On Self Test
A group of clearly defined OS-independent interface for
hardware
 Int10 for Video service
 Int13 disk service
 Int16 keyboard service
 Int18 BIOS ROM loader
 Int19 bootstrap loader
Availability of MS-DOS outside of IBM allowed applications
to run equally well across different brands of box "PC clones".
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BIOS background -- Legacy BIOS’s Flaws
It
is not platform independent, it highly depends
on Intel 8086 Software Interrupt model




Real mode
16-bits register access
No memory address beyond 1MB
Option ROM space limited to below 1MB
Modern
Intel CPU architecture has come to 32bits, 64bits
protection mode, with HT and Multi-core, but for
compatibility, it should still boot up in 16 bit real mode
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BIOS background – Flaws (cont.)
It
is inaccessible to boot 64bits system which still call
into 16 bit legacy firmware when Itanium processor
family come into life.

More and more new technology come out, like VT, LT
etc. It is very hard to enable those technology in the
whole eco-system quickly in legacy BIOS
 Architecture
independent is the key for the next
generation BIOS, that is where the EFI come from,
single driver can work in x86, Itanium and XScale etc.
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BIOS background – Flaws (cont.)
Code
Real Mode
Issue
Scalability
Assembler
Complexity
Spaghetti
Maintenance
Spec
None!
OS Loader
Tied to HW
and BIOS
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Compatibility
Slows innovation
Carries legacy
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BIOS background – Change
Extensible Firmware Interface
 UEFI is an interface specification
--download from www.uefi.org
 Abstracts the platform from OS
 Includes a modular driver model and
CPU-independent option ROMs
 Compatible by design
 Modular and extensible
 Complements existing interfaces
OS
Loader
UEFI
Firmware
Hardware
Flexible to meet existing and future needs
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Compatibility
 Unified
BIOS background – Change
Code
Real Mode
Issue
Scaleability
Assembler
Complexity
Spaghetti
Maintenance
Spec
None!
OS Loader
Tied to HW
and BIOS
继续
Compatibility
Slows innovation
Carries legacy
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