## 10.5 初始化示例
```
$TITLE ('Initial Task')
NAME INIT
init_stack SEGMENT RW
DW 20 DUP(?)
tos LABEL WORD
init_stack ENDS
init_data SEGMENT RW PUBLIC
DW 20 DUP(?)
init_data ENDS
init_code SEGMENT ER PUBLIC
ASSUME DS:init_data
nop
nop
nop
init_start:
; set up stack
mov ax, init_stack
mov ss, ax
mov esp, offset tos
mov a1,1
blink:
xor a1,1
out 0e4h,a1
mov cx,3FFFh
here:
dec cx
jnz here
jmp SHORT blink
hlt
init_code ends
END init_start, SS:init_stack, DS:init_data
$TITLE('Protected Mode Transition -- 386 initialization')
NAME RESET
;*****************************************************************
; Upon reset the 386 starts executing at address 0FFFFFFF0H. The
; upper 12 address bits remain high until a FAR call or jump is
; executed.
;
; Assume the following:
;
;
; - a short jump at address 0FFFFFFF0H (placed there by the
; system builder) causes execution to begin at START in segment
; RESET_CODE.
;
;
; - segment RESET_CODE is based at physical address 0FFFF0000H,
; i.e. at the start of the last 64K in the 4G address space.
; Note that this is the base of the CS register at reset. If
; you locate ROMcode above this address, you will need to
; figure out an adjustment factor to address things within this
; segment.
;
;*****************************************************************
$EJECT ;
; Define addresses to locate GDT and IDT in RAM.
; These addresses are also used in the BLD386 file that defines
; the GDT and IDT. If you change these addresses, make sure you
; change the base addresses specified in the build file.
GDTbase EQU 00001000H ; physical address for GDT base
IDTbase EQU 00000400H ; physical address for IDT base
PUBLIC GDT_EPROM
PUBLIC IDT_EPROM
PUBLIC START
DUMMY segment rw ; ONLY for ASM386 main module stack init
DW 0
DUMMY ends
;*****************************************************************
;
; Note: RESET CODE must be USEl6 because the 386 initally executes
; in real mode.
;
RESET_CODE segment er PUBLIC USE16
ASSUME DS:nothing, ES:nothing
;
; 386 Descriptor template
DESC STRUC
lim_0_15 DW 0 ; limit bits (0..15)
bas_0_15 DW 0 ; base bits (0..15)
bas_16_23 DB 0 ; base bits (16..23)
access DB 0 ; access byte
gran DB 0 ; granularity byte
bas_24_31 DB 0 ; base bits (24..31)
DESC ENDS
; The following is the layout of the real GDT created by BLD386.
; It is located in EPROM and will be copied to RAM.
;
; GDT[O] ... NULL
; GDT[1] ... Alias for RAM GDT
; GDT[2] ... Alias for RAM IDT
; GDT[2] ... initial task TSS
; GDT[3] ... initial task TSS alias
; GDT[4] ... initial task LDT
; GDT[5] ... initial task LDT alias
;
; define entries in GDT and IDT.
GDT_ENTRIES EQU 8
IDT_ENTRIES EQU 32
; define some constants to index into the real GDT
GDT_ALIAS EQU 1*SIZE DESC
IDT_ALIAS EQU 2*SIZE DESC
INIT_TSS EQU 3*SIZE DESC
INIT_TSS_A EQU 4*SIZE DESC
INIT_LDT EQU 5*SIZE DESC
INIT_LDT_A EQU 6*SIZE DESC
;
; location of alias in INIT_LDT
INIT_LDT_ALIAS EQU 1*SIZE DESC
;
; access rights byte for DATA and TSS descriptors
DS_ACCESS EQU 010010010B
TSS_ACCESS EQU 010001001B
;
; This temporary GDT will be used to set up the real GDT in RAM.
Temp_GDT LABEL BYTE ; tag for begin of scratch GDT
NULL_DES DESC <> ; NULL descriptor
FLAT_DES DESC <0FFFFH,0,0,92h,0CFh,0>
GDT_eprom DP ? ; Builder places GDT address and limit
; in this 6 byte area.
IDT_eprom DP ? ; Builder places IDT address and limit
; in this 6 byte area.
;
; Prepare operand for loadings GDTR and LDTR.
TGDT_pword LABEL PWORD ; for temp GDT
DW end_Temp_GDT_Temp_GDT -1
DD 0
GDT_pword LABEL PWORD ; for GDT in RAM
DW GDT_ENTRIES * SIZE DESC -1
DD GDTbase
IDT_pword LABEL PWORD ; for IDT in RAM
DW IDT_ENTRIES * SIZE DESC -1
DD IDTbase
end_Temp_GDT LABEL BYTE
;
; Define equates for addressing convenience.
GDT_DES_FLAT EQU DS:GDT_ALIAS +GDTbase
IDT_DES_FLAT EQU DS:IDT_ALIAS +GDTbase
INIT_TSS_A_OFFSET EQU DS:INIT_TSS_A
INIT_TSS_OFFSET EQU DS:INIT_TSS
INIT_LDT_A_OFFSET EQU DS:INIT_LDT_A
INIT_LDT_OFFSET EQU DS:INIT_LDT
; define pointer for first task switch
ENTRY POINTER LABEL DWORD
DW 0, INIT_TSS
;******************************************************************
;
; Jump from reset vector to here.
START:
CLI ;disable interrupts
CLD ;clear direction flag
LIDT NULL_des ;force shutdown on errors
;
; move scratch GDT to RAM at physical 0
XOR DI,DI
MOV ES,DI ;point ES:DI to physical location 0
MOV SI,OFFSET Temp_GDT
MOV CX,end_Temp_GDT-Temp_GDT ;set byte count
INC CX
;
; move table
REP MOVS BYTE PTR ES:[DI],BYTE PTR CS:[SI]
LGDT tGDT_pword ;load GDTR for Temp. GDT
;(located at 0)
; switch to protected mode
MOV EAX,CR0 ;get current CRO
MOV EAX,1 ;set PE bit
MOV CRO,EAX ;begin protected mode
;
; clear prefetch queue
JMP SHORT flush
flush:
; set DS,ES,SS to address flat linear space (0 ... 4GB)
MOV BX,FLAT_DES-Temp_GDT
MOV US,BX
MOV ES,BX
MOV SS,BX
;
; initialize stack pointer to some (arbitrary) RAM location
MOV ESP, OFFSET end_Temp_GDT
;
; copy eprom GDT to RAM
MOV ESI,DWORD PTR GDT_eprom +2 ; get base of eprom GDT
; (put here by builder).
MOV EDI,GDTbase ; point ES:EDI to GDT base in RAM.
MOV CX,WORD PTR gdt_eprom +0 ; limit of eprom GDT
INC CX
SHR CX,1 ; easier to move words
CLD
REP MOVS WORD PTR ES:[EDI],WORD PTR DS:[ESI]
;
; copy eprom IDT to RAM
;
MOV ESI,DWORD PTR IDT_eprom +2 ; get base of eprom IDT
; (put here by builder)
MOV EDI,IDTbase ; point ES:EDI to IDT base in RAM.
MOV CX,WORD PTR idt_eprom +0 ; limit of eprom IDT
INC CX
SHR CX,1
CLD
REP MOVS WORD PTR ES:[EDI],WORD PTR DS:[ESI]
; switch to RAM GDT and IDT
;
LIDT IDT_pword
LGDT GDT_pword
;
MOV BX,GDT_ALIAS ; point DS to GDT alias
MOV DS,BX
;
; copy eprom TSS to RAM
;
MOV BX,INIT_TSS_A ; INIT TSS A descriptor base
; has RAM location of INIT TSS.
MOV ES,BX ; ES points to TSS in RAM
MOV BX,INIT_TSS ; get inital task selector
LAR DX,BX ; save access byte
MOV [BX].access,DS_ACCESS ; set access as data segment
MOV FS,BX ; FS points to eprom TSS
XOR si,si ; FS:si points to eprom TSS
XOR di,di ; ES:di points to RAM TSS
MOV CX,[BX].lim_0_15 ; get count to move
INC CX
;
; move INIT_TSS to RAM.
REP MOVS BYTE PTR ES:[di],BYTE PTR FS:[si]
MOV [BX].access,DH ; restore access byte
;
; change base of INIT TSS descriptor to point to RAM.
MOV AX,INIT_TSS_A_OFFSET.bas_0_15
MOV INIT_TSS_OFFSET.bas_0_15,AX
MOV AL,INIT_TSS_A_OFFSET.bas_16_23
MOV INIT_TSS_OFFSET.bas_16_23,AL
MOV AL,INIT_TSS_A_OFFSET.bas_24_31
MOV INIT_TSS_OFFSET.bas_24_31,AL
;
; change INIT TSS A to form a save area for TSS on first task
; switch. Use RAM at location 0.
MOV BX,INIT_TSS_A
MOV WORD PTR [BX].bas_0_15,0
MOV [BX].bas_16_23,0
MOV [BX].bas_24_31,0
MOV [BX].access,TSS_ACCESS
MOV [BX].gran,O
LTR BX ; defines save area for TSS
;
; copy eprom LDT to RAM
MOV BX,INIT_LDT_A ; INIT_LDT_A descriptor has
; base address in RAM for INIT_LDT.
MOV ES,BX ; ES points LDT location in RAM.
MOV AH,[BX].bas_24_31
MOV AL,[BX].bas_16_23
SHL EAX,16
MOV AX,[BX].bas_0_15 ; save INIT_LDT base (ram) in EAX
MOV BX,INIT_LDT ; get inital LDT selector
LAR DX,BX ; save access rights
MOV [BX].access,DS_ACCESS ; set access as data segment
MOV FS,BX ; FS points to eprom LDT
XOR si,si ; FS:SI points to eprom LDT
XOR di,di ; ES:DI points to RAM LDT
MOV CX,[BX].lim_0_15 ; get count to move
INC CX
;
; move initial LDT to RAM
REP MOVS BYTE PTR ES:[di],BYTE PTR FS:[si]
MOV [BX].access,DH ; restore access rights in
; INIT_LDT descriptor
;
; change base of alias (of INIT_LDT) to point to location in RAM.
MOV ES:[INIT_LDT_ALIAS].bas_0_15,AX
SHR EAX,16
MOV ES:[INIT_LDT_ALIAS].bas_16_23,AL
MOV ES:[INIT_LDT_ALIAS].bas_24_31,AH
;
; now set the base value in INIT_LDT descriptor
MOV AX,INIT_LDT_A_OFFSET.bas_0_15
MOV INIT_LDT_OFFSET.bas_0_15,AX
MOV AL,INIT_LDT_A_OFFSET.bas_16_23
MOV INIT_LDT_OFFSET.bas_16_23,AL
MOV AL,INIT_LDT_A_OFFSET.bas_24_31
MOV INIT_LDT_OFFSET.bas_24_31,AL
;
; Now GDT, IDT, initial TSS and initial LDT are all set up.
;
; Start the first task!
'
JMP ENTRY_POINTER
RESET_CODE ends
END START, SS:DUMMY,DS:DUMMY
```
- 第一章 80386介绍
- 1.1 该手册的组织结构
- 1.2 其他文献
- 第二章 编程基本模型
- 2.1 存储器组织和段
- 2.2 数据类型
- 2.3 寄存器
- 2.4 指令格式
- 2.5 操作数选择
- 2.6 中断和异常
- 第4章 系统寄存器
- 4.1 系统寄存器 (System Registers)
- 4.2 系统指令 (System Instructions)
- 第五章 内存管理
- 5.1 分段地址转换（Segment Translation）
- 5.2 分页地址转换（Page Translation）
- 5.3 混合分段和分页地址转换（Combining Segment and Page Translation）
- 第六章 内存管理
- 6.1 为什么要保护（Why Protection?）
- 6.2 80386保护机制概述（Overview of 80386 Protection Mechnaisms）
- 6.3 段级保护（Segment-Level Protection）
- 6.4 页级保护（Page-Level Protection）
- 6.5 混合分页和分段保护（Combining Page and Segment Protection）
- 第7章 多任务（Multitasking）
- 8.1 I/O 寻址（I/O Addressing）
- 7.1 任务状态段（Task State Segment）
- 7.3 任务寄存器（Task Register）
- 7.4 任务门描述符（Task Gate Descriptor）
- 7.5 任务切换（Task Switching）
- 7.6 任务链（Task Linking）
- 7.7 任务寻址空间（Task Address Space）
- 第8章 输入 输出
- 8.2 I/O 指令（I/O Instructions）
- 8.3 保护和I/O（Protection and I/O）
- 第9章 异常和中断（Exceptions and Interrupts）
- 9.1 识别中断（Identifying Interrupts）
- 9.2 允许和禁止中断（Enabling and Disabling Interrupts）
- 9.3 同时发生的中断和异常的优先级（Priority Among Simultaneous Interrupts and Exceptions）
- 9.4 中断描述符表（Interrupt Descriptor Table）
- 9.5 IDT 描述符（IDT Descriptors）
- 9.6 中断任务和中断子程序（Interrupt Tasks and Interrupt Procedures）
- 9.7 出错码（Error Code）
- 9.8 异常条件（Exception Conditions）
- 9.9 异常总结（Exception Summary）
- 9.10 出错码总结（Error Code Summary）
- 第10章 初始化（Initialization）
- 10.1 复位后处理器状态（Processor State After Reset）
- 10.2 实模式初始化（Software Initialization for Real-Address Mode）
- 10.3 切换到保护模式（Switching to Protected Mode）
- 10.4 保护模式初始化（Software Initialization for Protected Mode）
- 10.5 初始化示例
- 10.6 TLB测试
- 第十四章 80386实地址模式
- 14.1 物理地址构成
- 14.2 寄存器和指令
- 14.3 中断和异常处理
- 14.4 进入和离开实地址模式
- 14.6 实地址模式异常
- 14.7 与8086的不同
- 14.8 与80286实地址模式的不同