linux 0.11时钟初始化,linux-0.11 初始化---Setup.s

!

! setup.s (C) 1991 Linus Torvalds

!

! setup.s is responsible for getting the system data from the

BIOS,

! and putting them into the appropriate places in system

memory.

! both setup.s and system has been loaded by the

bootblock.

!

! This code asks the bios for memory/disk/other parameters,

and

! puts them in a "safe" place: 0x90000-0x901FF, ie where

the

! boot-block used to be. It is then up to the protected

mode

! system to read them from there before the area is

overwritten

! for buffer-blocks.

!

! NOTE! These had better be the same as in bootsect.s!

INITSEG  = 0x9000 ! we move boot here - out

of the way

SYSSEG  = 0x1000 ! system loaded at 0x10000

(65536).

SETUPSEG = 0x9020 ! this is the current segment

.globl begtext, begdata, begbss, endtext, enddata,

endbss

.text

begtext:

.data

begdata:

.bss

begbss:

.text

entry start

start:

! ok, the read went well so we get current cursor position and

save it for

! posterity.

mov ax,#INITSEG ! this is done in bootsect already,

but...

mov ds,ax

mov ah,#0x03 ! read cursor pos

xor bh,bh

int 0x10 ! save it in known place, con_init fetches

mov [0],dx ! it from 0x90000.

把dx的值放入ds:si-->0x9000:0x0000处，即dx中的光标位置信息放入0x90000

! Get memory size (extended mem, kB)

！INT

15H功能88H

功能描述：读取扩展内存大小入口参数：AH＝88H出口参数：AX＝扩展内存字节数(以K为单位)

mov ah,#0x88

int 0x15

mov [2],ax ！0x90002处存放是扩展内存数

! Get video-card data:

!INT

10H 功能0FH

功能描述：读取显示器模式入口参数：AH＝0FH出口参数：AH＝屏幕字符的列数AL＝显示模式(参见功能00H中的说明)

BH＝页码

mov ah,#0x0f

int 0x10

mov [4],bx ! bh = display page !0x90004处存放显示页面

mov [6],ax ! al = video mode, ah = window width ！0x90006处存放video mode,window width

! check for EGA/VGA and some config parameters

mov ah,#0x12

mov bl,#0x10

int 0x10

mov [8],ax !0x90008/a/c存放显示的配置信息：显示内存/配置参数/显示状态

mov [10],bx

mov [12],cx

! Get hd0 data

mov ax,#0x0000

mov ds,ax

lds si,[4*0x41] !取中段向量0x41的值，也即hd0参数表的地址->ds:si

mov ax,#INITSEG

mov es,ax

mov di,#0x0080 !传输的目的地址：0x9000:0x0080->es:di

mov cx,#0x10 !共传输16字节

rep

movsb

! Get hd1 data

mov ax,#0x0000

mov ds,ax

lds si,[4*0x46] ！取中段向量0x46的值，也即hd1参数表的地址->ds:si

mov ax,#INITSEG

mov es,ax

mov di,#0x0090 !传输的目的地址：0x9000:0x0090->es:di

mov cx,#0x10

rep

movsb

! Check that there IS a hd1 :-)

！INT 13H 功能15H

功能描述：读取磁盘类型入口参数：AH＝15H

输入DL＝驱动器，00H~7FH：软盘；80H~0FFH：硬盘，80H第一个硬盘，81H第二个硬盘出口参数：CF＝1——操作失败，AH＝状态代码，参见功能号01H中的说明，

否则，AH＝00H

—未安装驱动器＝01H

—无改变线支持的软盘驱动器＝02H

—带有改变线支持的软盘驱动器＝03H

—硬盘，CX:DX＝512字节的扇区数

mov ax,#0x01500

mov dl,#0x81

int 0x13

jc no_disk1

cmp ah,#3

je is_disk1

no_disk1:

mov ax,#INITSEG

mov es,ax

mov di,#0x0090

mov cx,#0x10

mov ax,#0x00

rep

stosb ！把ax中的值存放在es:di指向的位置，每次di-1,目的是清除之前保存的HD1的参数表值

is_disk1:

! now we want to move to protected mode ...

cli ! no interrupts allowed !

! first we move the system to it's rightful place

mov ax,#0x0000

cld ! 'direction'=0, movs moves forward

do_move:

mov es,ax ! destination segment

add ax,#0x1000

cmp ax,#0x9000

jz end_move

mov ds,ax ! source segment

sub di,di

sub si,si

mov cx,#0x8000

rep

movsw

jmp do_move

! then we load the segment descriptors

end_move:

mov ax,#SETUPSEG ! right, forgot this at first. didn't work

:-)

mov ds,ax

lidt idt_48 ! load idt with 0,0

lgdt gdt_48 ! load gdt with whatever appropriate

! that was painless, now we enable A20

！为了访问1M以上的地址空间(物理内存)，需要开启A20的地址线。下面是开起A20地址线的方式

call empty_8042 ！清空键盘缓存区，只有当缓冲区为空时才可以写。

mov al,#0xD1 ! command write

out #0x64,al

call empty_8042

mov al,#0xDF ! A20 on

out #0x60,al

call empty_8042

! well, that went ok, I hope. Now we have to reprogram the

interrupts :-(

! we put them right after the intel-reserved hardware

interrupts, at

! int 0x20-0x2F. There they won't mess up anything. Sadly IBM

really

! messed this up with the original PC, and they haven't been

able to

! rectify it afterwards. Thus the bios puts interrupts at

0x08-0x0f,

! which is used for the internal hardware interrupts as well.

We just

! have to reprogram the 8259's, and it isn't fun.

mov al,#0x11 ! initialization sequence

out #0x20,al ! send it to 8259A-1

.word 0x00eb,0x00eb ! jmp $+2, jmp $+2

out #0xA0,al ! and to 8259A-2

.word 0x00eb,0x00eb

mov al,#0x20 ! start of hardware int's (0x20)

out #0x21,al

.word 0x00eb,0x00eb

mov al,#0x28 ! start of hardware int's 2 (0x28)

out #0xA1,al

.word 0x00eb,0x00eb

mov al,#0x04 ! 8259-1 is master

out #0x21,al

.word 0x00eb,0x00eb

mov al,#0x02 ! 8259-2 is slave

out #0xA1,al

.word 0x00eb,0x00eb

mov al,#0x01 ! 8086 mode for both

out #0x21,al

.word 0x00eb,0x00eb

out #0xA1,al

.word 0x00eb,0x00eb

mov al,#0xFF ! mask off all interrupts for now

out #0x21,al

.word 0x00eb,0x00eb

out #0xA1,al

! well, that certainly wasn't fun :-(. Hopefully it works, and

we don't

! need no steenking BIOS anyway (except for the initial

loading :-).

! The BIOS-routine wants lots of unnecessary data, and it's

less

! "interesting" anyway. This is how REAL programmers do

it.

!

! Well, now's the time to actually move into protected mode.

To make

! things as simple as possible, we do no register set-up or

anything,

! we let the gnu-compiled 32-bit programs do that. We just

jump to

! absolute address 0x00000, in 32-bit protected mode.

mov ax,#0x0001 ! protected mode (PE) bit

lmsw ax ! This is it!

jmpi 0,8 ! jmp offset 0 of segment 8 (cs)

! This routine checks that the keyboard command queue is

empty

! No timeout is used - if this hangs there is something wrong

with

! the machine, and we probably couldn't proceed anyway.

empty_8042:

.word 0x00eb,0x00eb

in al,#0x64 ! 8042 status port

test al,#2 ! is input buffer full?

jnz empty_8042 ! yes - loop

ret

gdt:

.word 0,0,0,0 ! dummy

.word 0x07FF ! 8Mb - limit=2047 (2048*4096=8Mb)

.word 0x0000  ! base address=0

.word 0x9A00 ! code read/exec

.word 0x00C0 ! granularity=4096, 386

.word 0x07FF ! 8Mb - limit=2047 (2048*4096=8Mb)

.word 0x0000 ! base address=0

.word 0x9200 ! data read/write

.word 0x00C0 ! granularity=4096, 386

idt_48:

.word 0 ! idt limit=0

.word 0,0 ! idt base=0L

gdt_48:

.word 0x800 ! gdt limit=2048, 256 GDT entries

.word 512+gdt,0x9  ! gdt base = 0X9xxxx

.text

endtext:

.data

enddata:

.bss

endbss: